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This is to certify that the
dissertation entitled

WEED CONTROL SYSTEMS IN SUGARBEET (Beta
vulgaris): TIMING OF POST MICRO-RATE HERBICIDES
USING GROWING DEGRE DAYS, AND VARIETY
RESPONSE TO POST HERBICIDES

presented by

Trevor M. Dale

has been accepted towards fulfillment
of the requirements for the

Ph.D degree in Crop and Soil Sciences

 

 

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WEED CONTROL SYSTEMS IN SUGARBEET (Beta vulgaris): TIMING OF POST
MICRO-RATE HERBICIDES USING GROWING DEGREE DAYS, AND VARIETY
RESPONSE TO POST HERBICIDES

By

Trevor M. Dale

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
Department of Crop and Soil Sciences

2003

ABSTRACT
WEED CONTROL SYSTEMS IN SUGARBEET (Beta vulgaris): TIMING OF POST
MICRO-RATE HERBICIDES USING GROWING DEGREE DAYS, AND VARIETY
RESPONSE TO POST HERBICIDES
By
Trevor M. Dale
Field and growth chamber studies were conducted to determine if sequential

micro-rate herbicide treatments based on growing degree days (GDD) controlled weeds
in sugarbeet. The micro-rate treatment (desmedipham plus phenmedipham (1 :1 ratio) at
0.09 kg ai/ha plus triflusulfuron at 0.004 kg ai/ha, plus clopyralid at 0.023 kg ae/ha, plus
methylated seed oil at 1.5% v/v) was applied three times, spaced every 97, 125, or 152
GDD with a base temperature of 1.1 C. In the growth chamber, common lambsquarters
and redroot pigweed control was excellent when the micro-rate treatment was applied
every 97 and 125 GDD; however, when the micro—rate treatment was applied every 152
GDD, redroot pigweed control decreased by 37%. In the field, common lambsquarters
control was excellent with all GDD treatments in 2001 and 2002. Amaranthus spp.
control was greater when micro-rates were applied every 7 d, every new leaf pair, or
every 97 GDD compared to micro-rates applied every 152 GDD or when scouted
(applications based on weed size) in 2001; however, control in all treatments was
greater than 90%. In 2002, Amaranthus spp. control was 86% when the micro-rate was
applied at the 7 d spacing and 80% when applied at the 152 GDD spacing. By applying
the micro-rate treatment using GDD instead of every 7 d, two or three micro-rate
applications could be eliminated while maintaining sucrose yields similar to, or greater,
than with the 7 d spacing. Small plot trials and strip trials in grower fields determined if
the micro-rate provided similar control to the same herbicide treatment applied twice at a
higher rate (desmedipham plus phenmedipham at 0.56 kg/ha plus triflusulfuron at 0.017

kg/ha plus clopyralid at 0.1 kg/ha, or desmedipham plus phenmedipham plus

ethofumesate at 0.28 kg/ha plus triflusulfuron at 0.017 kg/ha plus clopyralid at 0.1
kg/ha), and if preemergence (PRE) herbicides were required with the micro-rate or
standard-split applications. Common lambsquarters control was greatest with four
micro-rate applications of desmedipham plus phenmedipham plus ethofumesate
compared to four micro-rate applications of desmedipham plus phenmedipham when
combined over all PRE treatments. When no PRE herbicides were applied,
desmedipham plus phenmedipham plus ethofumesate applied in four micro—rate or two
standard-split applications provided greater control of common lambsquarters than
desmedipham plus phenmedipham applied as a micro-rate or a standard-split
application. Amaranthus spp. control was excellent ranging from 96 to 100% with all
postemergence (POST) herbicide treatments, and greater than 97% when combined
over PRE herbicide treatments in 2002. Field and growth chamber studies were
conducted to determine the response of several sugarbeet varieties and lines to micro-
rate herbicide treatments. In the growth chamber, three micro-rate treatments spaced
every 7 d reduced the leaf area of the fourteen sugarbeet varieties by 3 to 35%, and leaf
dry weight by 11 to 59% when measured 7 d after the last herbicide application. The
herbicides in the micro-rate reduced the leaf area of the USDA lines by 20 to 29% and
leaf dry weights by 47 to 53%. The commercial variety Hilleshog E-17 and the USDA
population 576 were the most tolerant to micro-rate herbicide treatments with a 3 and
20% reduction in leaf area, and 19 and 47% reduction in dry weight, respectively,
compared to the untreated controls. In the field, three micro-rate herbicide treatments
spaced every 7 d reduced the leaf area of the fourteen sugarbeet varieties by 3 to 40%,
and leaf dry weights by 2 to 44% compared to the untreated controls. The two
commercial varieties ACH 913 and ACH 1353 were the most tolerant to micro-rate

herbicide treatments.

AKNOWLEDGEMENTS

The author would like to express his deep gratitude to my advisor Dr. Karen
Renner for all the days spent training me for the best possible career in agriculture. We
spent considerable time rating plots, walking fields, digging up plants and discussing
field problems with growers; and these were “real" educational experiences. The
farmers of Michigan and other states have benefited from the hard work of Dr. Renner.
My committee members Drs. Donald Penner, Royal Heins, and Mitch McGrath altered
their personal and business schedules several times to accommodate my schedule and
spent considerable time discussing my project. I am extremely grateful to have had
such a great committee. The author would also like to deeply thank Gary Powell for all
of our quality conversations over the last three years. It takes a technician like Gary to
accomplish all of the research in a quality manner. Another research technician that was
instrumental in conducting my research was Tim Duckert, who was always willing to
help. Many fellow graduate and undergraduate students helped me through statistics,
data collection, spraying, and harvest. The author would like to thank Dr. Chad Lee, Dr.
Caleb Dalley, Aaron Franssen, Eric Nelson, Brad Fronning, Scott Bollman, Adrienne
Rich, Mark Bemards, Amy Guza, Corey Guza, Terry Schulz, Ryan Robinson, and T. J.
Ross. The author would also like to thank my father for introducing me to agriculture
and giving me that basic understanding of agriculture from a very young age. Our
families have been very supportive throughout my educational years and I would like to
thank all of them. My wife, Karen, has been wonderful throughout my graduate career
and is so great with our son Elijah. Finally, I would like to thank the Lord for giving me all

of the opportunities I have had.

TABLE OF CONTENTS

LIST OF TABLES .......................................................................................... vii
CHAPTER 1. REVIEW OF LITERATURE

INTRODUCTION ................................................................................... 1
WEED COMPETITION IN SUGARBEET .................................................... 2
HISTORY OF HERBICIDE USE IN SUGARBEET ........................................ 3
HISTORY OF HERBICIDE RATE REDUCTION IN SUGARBEET ................... 5

CURRENT AND PREVIOUS WEED CONTROL STATEGIES IN SUGARBEETJ
POSTEMERGENCE HERBICIDE APPLICATION TIMINGS IN SUGARBEET...7
THE USE OF GROWING DEGREE DAYS FOR CROP MANAGEMENT

DECISIONS .......................................................................................... 9
DIFFERENTIAL RESPONSE OF SUGARBEET VARIETIES TO

HERBICIDES ...................................................................................... 11
LITERATURE CITED ........................................................................... 13

CHAPTER 2. TIMING OF POSTEMERGENCE MICRO-RATE APPLICATIONS
BASED ON GROWING DEGREE DAYS IN SUGARBEET (Beta vulgaris)

ABSTRACT ........................................................................................ 17
INTRODUCTION ................................................................................. 19
MATERIALS AND METHODS ................................................................ 22
Growth chamber studies ............................................................ 22
Field studies ............................................................................ 23
RESULTS AND DISCUSSION ............................................................... 25
Growth chamber studies ............................................................ 25
POST micro-rate applications In the field In 2001 and 2002 ............ 25
Sugarbeet response In the field In 2001 and 2002 .............................. 26
Weed response ........................................................................ 26
LITERATURE CITED ........................................................................... 29
TABLE 1 ............................................................................................ 31
TABLE 2 ............................................................................................ 32
TABLE 3 ............................................................................................ 33
TABLE 4 ............................................................................................ 34
TABLE 5 ............................................................................................ 35
TABLE 6 ............................................................................................ 36
TABLE 7 ............................................................................................ 37

CHAPTER 3. EFFECT OF PREEMERGENCE AND POSTEMERGENCE HERBICIDES
ON WEED CONTROL AND SUGARBEET (Beta vulgaris) YIELD AND QUALITY

ABSTRACT ........................................................................................ 38
INTRODUCTION ................................................................................. 40
MATERIALS AND METHODS ................................................................ 43
Small plot field research ............................................................ 43
Strip trials in production fields ................................................... 45
RESULTS AND DISCUSSION ................................................................ 47

Small plot field research ............................................................ 47

Strip trials In production fields ................................................... 50
LITERATURE CITED ............................................................................ 52
TABLE 1 ............................................................................................ 53 ‘
TABLE 2 ............................................................................................ 54
TABLE 3 ............................................................................................ 55
TABLE 4 ............................................................................................ 56
TABLE 5 ............................................................................................ 57
TABLE 6 ............................................................................................ 58
TABLE 7 ............................................................................................ 59
TABLE 8 ............................................................................................ 60
TABLE 9 ............................................................................................ 61
TABLE 10 .......................................................................................... 62
TABLE 11 .......................................................................................... 63
TABLE 12 .......................................................................................... 64
TABLE 13 .......................................................................................... 65
TABLE 14 .......................................................................................... 66

CHAPTER 4. REPONSE OF SUGARBEET (Beta vulgaris) VARIETIES AND
POPULATIONS TO POSTEMERGENCE HERBICIDE TREATMENTS

ABSTRACT ........................................................................................ 67
INTRODUCTION .................................................................................. 69
MATERIALS AND METHODS ................................................................ 71

Growth chamber research .......................................................... 71

Field research ........................................................................... 72
RESULTS AND DISCUSSION ................................................................ 73

Growth chamber research .......................................................... 73

Field research ........................................................................... 73
LITERATURE CITED ............................................................................ 75
TABLE 1 ............................................................................................. 77
TABLE 2 ............................................................................................ 78
TABLE 3 ............................................................................................ 79
TABLE 4 ............................................................................................ 80
TABLE 5 ............................................................................................ 81

EXTENSION SUMMARY OF WEED MANAGEMENT SYSTEMS IN SUGARBEET....82

vi

LIST OF TABLES

CHAPTER 2. TIMING or POSTEMERGENCE MICRO-RATE APPLICATIONS
BASED ON GROWING DEGREE DAYS IN SUGARBEET (Beta vulgaris)

TABLE 1. DEVIATIONS FROM THE NORMAL MONTHLY PRECIPITATION
AND MEAN TEMPERATURE IN 2001 AND 2002 AT MICHIGAN STATE
UNIVERSITY HORTICULTURE TEACHING AND RESEARCH CENTER, EAST
LANSING, MI ...................................................................................... 31

TABLE 2. COMMON LAMBSQUARTERS AND REDROOT PIGWEED
CONTROL 28 DAYS AFTER PLANTING WITH TWO OR THREE POST
HERBICIDE TREATMENTS APPLIED EVERY 97, 125, AND 152 GROWING
DEGREE DAYS IN (C) IN GROWTH CHAMBERS ...................................... 32

TABLE 3. THE NUMBER OF DAYS AFTER PLANTING THAT MICRO-RATE
HERBICIDE TREATMENTS WERE APPLIED FOR THE APRIL 5, 2001 AND
APRIL 7, 2002 PLANTING DATES ......................................................... 33

TABLE 4. THE NUMBER OF DAYS AFTER PLANTING THAT THE MICRO-
RATE HERBICIDE TREATMENTS WERE APPLIED FOR THE APRIL 19, 2001
AND APRIL 17, 2002 PLANTING DATES ................................................. 34

TABLE 5. THE NUMBER OF DAYS AFTER PLANTING THAT THE MICRO-
RATE HERBICIDE TREATMENTS WERE APPLIED FOR THE MAY 2, 2001
AND MAY 3, 2002 PLANTING DATES35

TABLE 6. SUGARBEET INJURY AND YIELD AS AFFECTED BY HERBICIDE
TREATMENTS IN 2001 AND 2002, AVERAGED OVER VARIETIES AND
PLANTING DATES .............................................................................. 36

TABLE 7. COMMON LAMBSQUARTERS AND AMARANTHUS SPECIES
CONTROL BY HERBICIDE TREATMENTS IN 2001 AND 2002, AVERAGED
OVER VARIETIES AND PLANTING DATES ............................................. 37

CHAPTER 3. EFFECT OF PREEMERGENCE AND POSTEMERGENCE HERBICIDES
ON WEED CONTROL AND SUGARBEET (Beta vulgaris) YIELD AND QUALITY

TABLE 1. SOIL SERIES, TYPE, ORGANIC MATTER, AND PLANTING DATES
FOR SMALL PLOT RESEARCH TRIALS AT EACH LOCATION IN 2001 AND
2002 .................................................................................................. 53

TABLE 2. DEVIATIONS FROM THE NORMAL MONTHLY PRECIPITATION
AND MEAN TEMPERATURE IN 2001 AND 2002 AT MICHIGAN STATE
UNIVERSITY SAGINAW VALLEY BEET 8: BEAN RESEARCH FARM,
SAGINAW, MI ..................................................................................... 54

TABLE 3. HERBICIDE, RATE, APPLICATION TIMING, NUMBER OF

APPLICATIONS, AND HERBICIDE PROGRAMS USED IN SMALL PLOT
RESEARCH TRIALS IN 2001 AND 2002 .................................................. 55

vii

TABLE 4. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM POST HERBICIDES
COMBINED AT THREE LOCATIONS IN 2001 ........................................... 56

TABLE 5. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM POST HERBICIDES
COMBINED OVER PRE HERBICIDES AT THREE LOCATIONS IN 2001 ....... 57

TABLE 6. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM PRE HERBICIDES AT
THREE LOCATIONS IN 2001 ................................................................. 58

TABLE 7. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM PRE HERBICIDES

COMBINED OVER POST HERBICIDES AT THREE LOCATIONS IN 2001 ..... 59

TABLE 8. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM POST HERBICIDES AT
TWO LOCATIONS IN 2002 .................................................................... 60

TABLE 9. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM POST HERBICIDES
COMBINED OVER PRE HERBICIDES AT TWO LOCATIONS IN

2002 .................................................................................................. 61

TABLE 10. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM PRE HERBICIDES
COMBINED OVER POST HERBICIDES AT TWO LOCATIONS IN 2002 ........ 62

TABLE 11. SUGARBEET INJURY AND POPULATION, AMARANTHUS
SPECIES AND COMMON LAMBSQUARTERS CONTROL, AND
RECOVERABLE SUCROSE PER HECTARE FROM PRE HERBICIDES AT
TWO LOCATIONS IN 2002 .................................................................... 63

TABLE 12. SUGARBEET STAND AND RECOVERABLE WHITE SUCROSE
PER HECTARE COMBINED OVER TROMBLE FARMS 2001, LARACHA
FARMS 2001 AND 2002, WACKERLE FARMS 2002, AND HELMRICH FARMS
2002 .................................................................................................. 64

TABLE 13. SUGARBEET STAND AND RECOVERABLE WHITE SUCROSE
PER HECTARE AT MAXWELL FARMS IN 2001 ........................................ 65

viii

TABLE 14. SUGARBEET STAND AND RECOVERABLE WHITE SUCROSE
PER HECTARE AT DAVE TROMBLE FARMS IN 2002 ............................... 66

CHAPTER 4. REPONSE OF SUGARBEET (Beta vulgaris) VARIETIES AND
POPULATIONS TO POSTEMERGENCE HERBICIDE TREATMENTS

TABLE 1. FRESH WEIGHT, DRY WEIGHT, AND LEAF AREA OF FOUR
COMMERCIAL SUGARBEET VARIETIES FOLLOWING THREE MICRO-RATE
HERBICIDE TREATMENTS IN THE GROWTH CHAMBER ......................... 77

TABLE 2. FRESH WEIGHT, DRY WEIGHT, AND LEAF AREA OF FOUR
USDA SUGARBEET POPULATIONS FOLLOWING THREE MICRO-RATE
HERBICIDE TREATMENTS IN THE GROWTH CHAMBER AND IN THE

FIELD ................................................................................................ 78

TABLE 3. FRESH WEIGHT, DRY WEIGHT, AND LEAF AREA OF
FOURTEEN COMMERCIAL SUGARBEET VARIETIES FOLLOWING THREE
MICRO-RATE HERBICIDE TREATMENTS IN THE GROWTH CHAMBER......79

TABLE 4. FRESH WEIGHT, DRY WEIGHT, AND LEAF AREA OF
FOURTEEN COMMERCIAL SUGARBEET VARIETIES FOLLOWING THREE
MICRO-RATE HERBICIDE TREATMENTS IN THE FIELD ........................... 80

TABLE 5. LEAF AREA AND DRY WEIGHT REDUCTIONS FOLLOWING
THREE HERBICIDE APPLICATIONS OF 16 SUGARBEET VARIETIES IN THE
GROWTH CHAMBER AND IN THE FIELD ................................................ 81

CHAPTER 1

REVIEW OF LITERATURE

INTRODUCTION

Sugarbeet (Beta vulgaris L.) and sugarcane (Saccharum spp.) are the two major
sources of sucrose production in the United States. Sugarbeet is grown in temperate
regions of the United States and sugarcane is grown in tropical and subtropical regions.
The first sugarbeet processing factory in the United States was built in 1838 in
Northhampton, MA (Cooke and Scott 1993a). Sugarbeet is a biennial and is a member
of the Chenopodiaceae family. Most of the sugarbeet grown in the United States is for
sucrose and is harvested prior to the reproductive growth stage, except for a limited area
in Oregon and Utah where seed is produced (Cooke and Scott 1993b). Sugarbeet was
grown on 665,354 hectares in the United States in 2002 (Anonymous 2003a). In 2002,
63,482 tons of sucrose was produced in the United States, and beet sugar accounted for
43% of the total production. The sucrose from the sugarbeet crop contributed over one
billion dollars to the United States economy in 2001 (Anonymous 2003b).

In the United States, there are five major regions where sugarbeet is grown.
These regions include the Red River Valley of Minnesota and North Dakota, the Great
Lakes region of Michigan, Ohio, and Ontario, the Northwest including Idaho and Oregon,
the lntermountain region including Colorado, Nebraska, and Wyoming, Montana, and the
Western region including California (Cooke and Scott 1993c). This wide range in
growing regions provides some universal and some specific production problems within
each region. Most of the sugarbeet grown in the lntermountain region, Northwest
region, and California is irrigated; however, most of the sugarbeet grown in the Red
River Valley region and the Great Lakes region is not irrigated. In California, sugarbeet

is planted in the late fall and is harvested nearly 12 months later, whereas all other

sugarbeet is planted in the spring and harvested in the fall of the same year. One of the
major limitations of sugarbeet production is the inability to process sucrose from the
sugarbeet rapidly without loosing significant amounts of sucrose to respiration in storage
(Anonymous 1998). This is a major advantage to the Northern climate of the Red River
Valley where sugarbeet can be frozen and stored which extends the processing of

sugarbeet into May.

WEED COMPETITION IN SUGARBEET

Sugarbeet is often the most important cash crop in the rotation, and is typically
followed by a cereal crop like wheat or corn. Although sugarbeet growers face many
challenges, weed control continues to be the most serious production problem (Luecke
and Dexter 2003a), and weeds occur in all sugarbeet production areas (Schweizer and
Dexter 1987). Competition from uncontrolled annual weeds can suppress sugarbeet so
severely that no crop is produced (Schweizer and Dexter 1987). Sugarbeet is a low
growing crop and many weeds grow taller than sugarbeet. Weeds that become taller will
be more competitive for light interception than those weeds that do not overtop the crop.
Crop loss due to competition is only one of the problems that weeds may cause. Weeds
may also cause harvest problems, reduce the quality of the harvested product, produce
seed that increases future weed problems, act as co-hosts for insects and diseases,
increase tillage needed for weed control, and reduce animal and human health (Dexter
2003)

Weeds that emerge soon after planting sugarbeet are more competitive than late
emerging weeds (Dawson 1965). Approximately 70% of the weeds found in sugarbeet
crops are broadleaves and 30% are grasses (Cooke and Scott 1993). Broadleaf weeds

generally are considered more competitive than grasses (Brimhall et al. 1965). For

example, one green foxtail plant per sugarbeet plant reduced yield by 26% in Wyoming,
compared to 70% for one redroot pigweed (Amaranthus retroflexus L.) plant (Brimhall et
al. 1965). In Washington, uncontrolled bamyardgrass reduced yields by 49%, compared
with 94% for common lambsquarters (Dawson 1965). In Nebraska, weeds that emerged
with sugarbeet and grew the entire season reduced root yield 90% (Wicks and Wilson
1983). Dawson (1965) found sugarbeet growing in Washington State needed a 12-
week, weed-free period to produce optimum yields.

Although growers spend significant time and money to control weeds, 1 to 5% of
the total annual weed population usually escapes control and competes with the crop
(Schweizer and Dexter 1987). Even low densities of tall, broadleaf weeds can reduce
root yields. For example, in Wyoming, eight redroot pigweed plants/30 m of row reduced
yields 16% (Brimhall 1965). In Colorado, yields were decreased when one common
sunflower (Schweizer and Bridge 1982), four kochia (Schweizer 1973), four to six
common lambsquarters (Schweizer 1983), or nine to eleven Powell amaranth
(Schweizer and Lauridson 1985) plants/30 m of row competed all season. In Minnesota,
a density of one redroot pigweed plant plus one wild cat plant/m of row reduced yields

by 24% (Dexter and Evans 1985).

HISTORY OF HERBICIDE USE IN SUGARBEET

In the 1940s, weeds were controlled in sugarbeet primarily with mechanical
implements, such as cultivators, rotary hoes, and tine weeders, and by cross cultivation,
short-handled hoes, and hand weeding by “stoop” labor (Schweizer and Dexter 1987).
Hand labor was required because sugarbeet seed was multigerm so thinning and weed
control occurred simultaneously. Chemical weed control, if used, was confined to

inorganic chemicals, such as sodium and potassium chloride which were applied at rates

of 225 to 450 kg/ha (Grigsby and Stahler 1950). In the late 19405, researchers began to
evaluate organic chemicals, such as propham, sodium TCA, and endothall (Cormany
and Eckroth 1952). In the early 19505, preemergence (PRE) mixtures of TCA plus
endothall were used extensively to control grasses and broadleaf weeds (Cormany
1954). Annual grasses were controlled effectively for the first time with dalapon (Warren
1954). In the 19505, EPTC and pebulate were developed as preplant soil incorporated
treatments and used principally in the semiarid regions of the United States (Bandeen et
al. 1959, Anderson and Jones 1963). In the 19605, diallate and mixtures of diallate plus
pebulate were used to control wild oats (Sullivan et al. 1963), and trifluralin, EPTC,
chlorpropham, and propham were developed for use as layby treatments. Also in the
19605, researchers evaluated pyrazon, cycloate, desmedipham, and phenmedipham;
herbicides still used today. Clopyralid was discovered in 1961, but was not marketed in
the United States until 1987 and was registered for use in sugarbeets in 1988 (Vencill
2002).

Since the 19605, there have been very few registrations of herbicides in
sugarbeet. The most recent herbicide registrations were sethoxydim and clopyralid in
the 19805, and clethodim, quizalofop, and triflusulfuron in the 19905. Sethoxydim,
clethodim, and quizalofop effectively control annual and perennial grass weeds
postemergence (Vencill 2002). Both clopyralid and triflusulfuron are very effective
broadleaf herbicides with very different weed spectrums and modes of action. Clopyralid
is the only growth regulator herbicide and triflusulfuron is the only acetolactase synthase
(ALS) inhibiting herbicide for selectively controlling weeds in sugarbeet. Triflusulfuron
controls kochia (not ALS resistant) and velvetleaf (Dexter et al. 2001; Starke and Renner
1996), and clopyralid controls several thistle species, common ragweed, and common
cocklebur very well (Vencill 2002). These weed species are very competitive and were

very difficult to control with other registered herbicides. Since the 19605, registration of

propham, sodium TCA, endothall, dalapon, pebulate, diallate, trifluralin, and
chlorpropham have been discontinued in sugarbeet.

Preemergence herbicide use has decreased significantly since the registration of
clopyralid and triflusulfuron, two very effective postemergence (POST) herbicides.
Luecke and Dexter (2002b) reported that PRE herbicide use has steadily declined from
96% of the sugarbeet hectares in 1984 to 4% in 2002. The option of greater POST
weed control with clopyralid and triflusulfuron has given growers the option of not using
PRE herbicides which are very expensive, and often provide only sporadic weed control,
depending upon environmental conditions and soil types (Renner and Powell 1991;
Hendrick et al. 1974). However, Michigan sugarbeet growers still applied PRE
herbicides on approximately 75% of the sugarbeet ha in 2001 and 60% in 2002‘. Due to
the great expense, the PRE herbicides are applied in a band over the crop row and then

growers depend on POST herbicides and/or between-row cultivation for weed control.

HISTORY OF HERBICIDE RATE REDUCTION IN SUGARBEET

Research on the use of reduced-rate, split-applications of phenmedipham began
in 1972 (Dexter 1994). In a typical experiment at one location, split applications (50% of
the standard use rate applied twice, seven to fourteen d apart) gave less sugarbeet
injury and superior weed control compared with a single full-rate application.
Desmedipham applied at 0.28 kg/ha followed by (fb) 0.28 kg/ha 7 to 14 d later,
controlled weeds better and tended to injure sugarbeet less than desmedipham at 1.12
kg/ha or split applications of 0.56/0.56 kg/ha. The selectivity of desmedipham and
phenmedipham is based on the rate of metabolism in the sugarbeet and weeds.

Sugarbeet metabolized 83 and 94% of the translocated phenmedipham and

 

' Renner, K. A. Annual sugarbeet grower survey 2002.

desmedipham, respectively, in 24 h (Hendrick et al. 1974). However, desmedipham
metabolism by wild mustard and redroot pigweed was significantly less. This difference
in the rate of metabolism is at least partially responsible for the greater weed control and
reduction in sugarbeet injury when using reduced-rate, split or multiple applications.

Split applications at reduced herbicide rates were widely used by 1980, and were the
primary POST weed control option until 1998 when the micro-rate was registered.
However, when growers use split-rates, treatments still have to be applied in the evening
hours to avoid excessive injury to sugarbeet.

In 1996, Warner (Warner 1996) discovered a synergism among desmedipham,
triflusulfuron, and clopyralid. The significant rate reductions of 65 to 75%, with the
addition of a methylated seed oil (MSO), resulted in weed control similar to that achieved
by standard rates. Further research with this combination resulted in the micro-rate,
currently used on a majority of the sugarbeet hectares grown in the United States since
1998. The micro-rate system utilizes a combination of desmedipham, or desmedipham
plus phenmedipham (1:1), or desmedipham plus phenmedipham plus ethofumesate
(1 :1:1) at 0.09 kg ai/ha plus triflusulfuron at 0.004 kg ai/ha plus clopyralid at 0.03 kg
ae/ha plus MSO at 1.5% v/v applied multiple times. The micro-rate was registered in
Minnesota and North Dakota in 1998, and Michigan, Nebraska, Wyoming, Montana, and
Idaho in 2000. In 2002, nearly all sugarbeet grown in the United States was treated with
reduced herbicide rates at least two times and many sugarbeet he were treated three to
five times. Advantages of the micro-rate include the ability to apply herbicides throughout
the day, reduced sugarbeet injury, reduced between-row cultivation, and reduced
herbicide use. However, application timing with respect to weed size becomes more
critical with the micro-rate compared to the standard rate, and typically four micro-rate
applications are required for complete weed control compared to two to three

applications with standard-rate applications.

CURRENT AND PREVIOUS WEED CONTROL STRATEGIES IN
SUGARBEET

Weed control in sugarbeet involves herbicides, cultivation, and hand labor. In
recent years, the use of herbicides has increased while cultivation and hand labor has
decreased. In a recent survey growers in eastern North Dakota and western Minnesota
indicated that sugarbeets were treated with herbicides 4.3 times in 2002, compared to
3.2 times in 1990 (Luecke and Dexter 2003b). This suggests that the implementation of
the micro-rate increased the total applications by one compared to the traditional
standard-split, because the standard-split was usually preceded by a PRE treatment.
Survey respondents reported the number of hand weeded ha had declined from 72% in
1995 to 32% in 2002. In addition to the decrease in hand weeded ha, the number of
cultivations also decreased from 3.2 times in 1992 to 1.9 times in 2002.

Similar trends are occurring in Michigan as the use of PRE herbicides has
decreased by 35% from 1998 to 2002, and the number of cultivations has declined to
two or fewer on 65% of the sugarbeet during the same time period‘. A typical weed
control program prior to the registration of the micro-rate involved a PRE herbicide
followed by 1 or 2 standard split POST treatments and 3 or 4 between-row cultivations.
In 2002, most sugarbeet growers broadcast applied the micro-rate three- to- five times,

did not use a PRE herbicide, and limited cultivation to one or two times.

POSTEMERGENCE HERBICIDE APPLICATION TIMINGS IN
SUGARBEET
Herbicide rates have been reduced and split-applied since the early 19705

(Dexter 1994). This split-application has typically included a herbicide application at the

cotyledon to two-leaf growth stage with subsequent applications occurring every 7-d

after the initial treatment (Starke and Renner1996, Morishita and Downward 1995, and
Miller et al. 1997). However, researchers have also reported applying follow-up
treatments based on “leaf-pair". This would typically include applying the first POST
application at the cotyledon to two-leaf stage and follow-up treatments at the four-leaf
and six-leaf stages depending on the number of applications (Wilson 1994, Wilson 1999,
and Wilson et al. 2002). Both application methods can be difficult to manage. Growers
following the 7-day schedule reduced the number of days between applications if rain or
wind was predicted for the 7th day. Timing herbicide applications based on leaf-pair is
very difficult because there is so much variability in sugarbeet emergence in most field
conditions. It is not uncommon to have sugarbeet ranging from cotyledon to six true
leaves in the same field. In addition, sugarbeet leaves are not opposite so they do not
appear in true pairs. Therefore, it is very difficult to differentiate between two, three, or
even four leaf sugarbeet. Furthermore, new leaves develop rapidly with each new leaf
requiring somewhat fewer GDD than the preceding one (Holen and Dexter 1996).

Split applications of herbicides and applying by calendar days or sugarbeet leaf-
pairs is more effective than single applications, but may be subject to weather conditions
and the judgment of the person scouting the field in their determining of a “new" leaf-
pair. The average daily temperature typically increases significantly from the time of the
first application to time of the last herbicide application especially when applying three or
four treatments. Depending on environmental conditions the average daily temperature
may also decline between applications. Both an increase and a decrease in
temperature affects the emergence and growth of weeds and sugarbeet. Cool overcast
conditions over extended time periods delays weed emergence and growth. Warm
sunny conditions will progress weed and sugarbeet growth. Furthermore, temperature
influences weed and crop species differently (Pearcy et al. 1981; Roman et al. 1999).

Pearcy et al. (1981) compared the relative growth rate of common lambsquarters a C3

plant, and redroot pigweed at C4 plant at three different temperature regimes. The
relative growth rate of common lambsquarters was greater than redroot pigweed when
the day/night temperature was 17/14 C, however at 25/18 C the relative growth rate was
similar, and at 34/28 C redroot pigweed growth rate was 26% greater than common
lambsquarters. Thus, there is a clear shift from a competitive advantage for common
lambsquarters at low temperatures to an advantage for redroot pigweed at high
temperatures. Roman et al. (1999) also compared the growth rate of common
lambsquarters and redroot pigweed at various temperature regimes, and found that both
shoot and root growth differed between species depending on temperature, and the two
species had different optimum temperatures. Therefore, improper application timings
using the 7-d or leaf-pair schedules may result in excessive sugarbeet injury and

herbicide use, and inadequate weed control.

THE USE OF GROWING DEGREE DAYS FOR CROP MANAGEMENT
DECISIONS

Temperature is considered the primary factor determiningIthe rate at which
plants develop although other factors including daylength, moisture and light may modify
the effects of temperature on the plant (Holen and Dexter 1996). Growers often use
calendar days to predict plant development for management decisions. However,
calendar days can be misleading, especially for early season crop growth stages when
temperatures may be well below or above the historical average. Growing degree days
(GDD) are a measure of the heat accumulation for a given period of time. GDD are able
to predict crop and insect development regardless of differences in temperatures from
year to year provided other environmental conditions are not limiting. Many different

methods can be used to measure GDD, but the most common method by far is the

“high/low” method, because the math is very simple. This method subtracts the base
temperature from the average daily temperature, which provides the GDD accumulated
per day.

The use of GDD using air temperature to predict plant development has been
used successfully for various crops (Vinocur and Ritchie 2001, Juskiw et al. 2001) and
weeds (Nord et al. 1999, Ball et al. 1995). Vinocur and Ritchie (2001) reported that com
(Zea mays L.) development was more accurately predicted if surface soil temperatures
were used until the apex is above the soil surface, and air temperatures were used after
that point. Juskiw et al. (2001) reported that spring barley (Hordeum vulgare L.)
development could be predicted using GDD based on air temperature, but plant
development from emergence to physiological maturity differed between varieties. Nord
et al. (1999) compared the growth of spring wheat (Triticum aestivum L.), kochia (Kochia
scoparia L.), and Russian thistle (Salsola iben’ca) under constant temperatures of 15, 23,
and 30 C. Spring wheat development in response to GDD was similar at 15 and 23 C
but was delayed at 30 C. The optimum temperature for spring wheat development was
25 C, and the base temperature was 4 C. Their data suggested that temperatures at or
below the optimum temperature provided better estimates of development by GDD than
temperatures above the optimum growth temperature. Roman at al. (1999) reported the
optimum temperature for common lambsquarters (Chenopodium album L.) development
is 25.2 C, and Oryokot et al. (1997) reported the Optimum temperature for redroot
pigweed is 32.9 C.

Many researchers have tried to predict weed seed germination and emergence
based on soil temperature and soil moisture (Roman et al. 2000, Oryokot et al. 1997,
Harvey and Forcella 1993, Forcella 1993). In controlled environments, success in
determining the temperature and rate of emergence of many weeds has been achieved.

However, this usually determines the time of 50% germination or emergence of the

10

weeds (Oryokot et al. 1997, Harvey and Forcella 1993, AIm et al.1993). In field
conditions, when weeds have reached 50% emergence the timing is probably too late for
POST weed control in sugarbeet, because a certain percentage of weeds would exceed
the size controlled by the herbicides. Roman et al. (2000) stated that the use of soil
temperature to calculate GDD was a better predictor of common lambsquarters seedling
emergence than air temperatures. However, this was only true at one of the two
locations in one of the two years, and only under no-till conditions. The difference in
predicting emergence was attributed to increased heterogeneity in the soil matrix and
vertical distribution of the seedbank caused by the chisel or moldboard plow (Buhler
1992). Most of the sugarbeet grown in the US. is planted in fields that have either been

chisel plowed or moldboard plowed the previous fall.

DIFFERENTIAL RESPONSE OF SUGARBEET VARIETIES TO
HERBICIDES

The crop response and weed control of many POST herbicides is greatly
affected by temperature. In fact, most POST herbicide labels provide a range of
temperatures in which the particular herbicide should be applied and what weed control
or crop response might be expected outside of that range. Often, lower temperatures of
10 to 15.6 C are associated with very little crop response and poor weed control,
whereas higher temperatures of 26.7 to 32.3 C are associated with greater weed control
and crop response. Temperatures prior to, or after the herbicide application can also
affect the response from the herbicide treatment (Mayo and Dexter 1997).

Previous research with sugarbeet varieties indicated a differential response to
herbicides among varieties. Dexter and Kern (1977) reponed the presence of cultivar by

herbicide interactions when higher than recommended rates of EPTC were applied.

11

There was no clear distinction between varieties; however, data indicated a slight
advantage in extractable sugar with diploid compared to triploid varieties. Smith and
Schweizer (1983) reported that all characters including plant weight, harvest root weight,
and foliar suppression differed among the eight commercial varieties tested when
treated with both preemergence herbicides and postemergence herbicides. The two
triploid varieties ‘Beta 1237’ and ‘GW D7’ had greater leaf area 45 days after treatment,
averaged over 1979 and 1980. In 1999, Wilson reported differences in leaf area, root
yield, and percent sucrose among the nine varieties treated with herbicide. In all cases,
there were no distinctions between the diploid and triploid varieties. These researchers
concluded that varietal response to herbicides may vary by year and location. In
addition to environmental conditions, the quality of sugarbeet seed varies greatly from
year to year depending on the growing conditions of the seed crop and other factors
including the seed coating process, and pesticide treatment of seeds (J. M. McGrath,
personal communication). Furthermore, sugarbeet varieties respond differently to other
early season stresses like temperature extremes, inadequate or excessive moisture, soil
pathogens, and herbicide treatments (personal observation). Therefore, it is often very
difficult to compare varieties in the field, because of the other stresses involved and the
interaction of these stresses and those added by herbicides. Because seed quality
varies significantly, the seed used in these experiments should be from the same seed

lot to minimize variability.

12

LITERATURE CITED

Alm, D. M. E. W. Stoller, and L. M. Wax. 1993. An index model for predicting seed
germination and emergence rates. Weed Technol. 7:560-569.

Anderson, G. W. and G. E. Jones. 1963. A progress report on chemical weed control in
sugar beets at Ontario Agricultural College. Proc. Am Soc. Sugar Beet Technol.
12:23-26.

Anonymous. 1998. The Sugarbeet Industry in California. California Beet Growers
Association, Ltd. Web page:
http://www.suqa_rbeet.ucdavis.edu/suqaLindustry.html. Accessed: May 23, 2003.

Anonymous. 2003a. Sugarbeets: Area, yield, and production, by States, 2000-2002.
Agricultural Statistics Board, NASS, and USDA: Web page:
http://wwwusdagov/nassl. Accessed: May 20, 2003.

 

Anonymous. 2003b. Sugarbeets: Area, yield, and production, marketing year average
price per ton received by farmers, value, and sugar production, United States,
1993-2002.

Agricultural Statistics Board, NASS, and USDA: Web page: http://www.usda.qov/na_ss_/.
Accessed: May 20, 2003.

Ball, D. A.., B. Klepper, and D. J. Rydrych. 1995. Comparative above-ground
development rates for several annual grass weeds and cereal grains. Weed Sci.
43:410-416.

Bandeen, J. D., C. M. Switzer, and G. E. Jones. 1959. An investigation of preplanting
soil incorporation of herbicides for the control of weeds in sugar beets. Proc. Am.
Sugar Beet Technol. East, US. and Canada. 10:41-44.

Brimhall, P. B., E. W. Chamberlain, and H. P. Alley. 1965. Competition of annual weeds
in sugarbeets. Weeds 13:33-35.

Cooke, D. A. and R. K. Scott. 1993a. The Sugar Beet Crop. 1St ed. Cambridge University
Press. 21 p.

Cooke, D. A. and R. K. Scott. 1993b. The Sugar Beet Crop. 1m ed. Cambridge University
Press. 122 p.

Cooke, D. A. and R. K. Scott. 1993c. The Sugar Beet Crop. 1St ed. Cambridge University
Press. 28 p.

Cormany, C. E. 1954. Pre-emergence applications of a combination of TCA and
endothal show promise for control of grassy and broadleaf weeds in sugar beets.
Proc. Am. Soc. Sugar Beet Technol. 8:135.

Cormany, C. E. and E. G. Eckroth. 1952. Results with TCA on barnyard grass control in

sugar beets in Montana and Wyoming. Proc. Am. Soc. Sugar Beet Technol.
7:126-127.

13

Dawson, J. H. 1965. Competition between irrigated sugarbeets and annual weeds.
Weeds 13:245-249.

Dexter, A. G. 1994. History of sugarbeet (Beta vulgaris) herbicide rate reduction in North
Dakota and Minnesota. Weed Technol. 8:334-337.

Dexter, A. G. 2003. Weed control guide for sugarbeet. Sugarbeet Res. Ext. Rep. 33:3.

Dexter, A. G., D. L. Vincent Ill, and J. L. Luecke. Control of Kochia with registered
herbicides. Sugarbeet Res. Ext. Rep. 32:77-83.

Dexter, A. G. and J. Kern. 1978. Response of sugarbeet varieties to Eptam and
Betanex, 1976 to 1978. Sugarbeet Res. Ext. Rep. 9:67-69.

Dexter, A. G. and R. R. Evans. 1985. Environmental factors affecting weed number
threshold. Abstr. Weed Sci. Soc. Am. p 59.

Forcella, F. 1993. Seedling emergence model for velvetleaf. Agron. J. 85:929-933.

Grigsby, B. H. and L. M. Stahler. 1950. Latest developments in the use of herbicides for
selective weed control in sugar beets. Proc. Am. Soc. Sugar Beet Technol.
6:463—467.

Harvey, S. J., and F. Forcella. 1993. Vernal seedling emergence model for
lambsquarters (Chenopodium album). Weed Sci. 41:309-316.

Hendrick, L. W., W. F. Meggitt, and D. Penner. 1973. Selective use of phenmedipham
and EP-475 in Michigan for weed control in sugarbeets. J. Am. Soc. Sugar Beet
Technol. 18:97-107.

Holen, C. D. and A. G. Dexter. 1996. A growing degree day equation for early sugarbeet
leaf stages. Sugarbeet Res. Ext. Rep. 27:152-157.

Juskiw, P. E., Y. W. Jame, and L. Kryzanowski. 2001. Phenological development of
spring barley in a short-season growing area. Agron. J. 93:370-379.

Luecke J. L. and A. G. Dexter. 2003a. Survey of weed control and production practices
on sugarbeet in eastern North Dakota and Minnesota. Sugarbeet Res. Ext. Rep.
33:38.

Luecke J. L. and A. G. Dexter. 2003b. Survey of weed control and production practices
on sugarbeet in eastern North Dakota and Minnesota. Sugarbeet Res. Ext. Rep.
33:35.

Mayo, C. M. and A. G. Dexter. 1997. Influence of Betanex plus frost on sugarbeet.
Sugarbeet Res. Ext. Rep. 28:111-112.

Miller, S. D., K. J. Fomstrom, and L. J. Held. 1997. Preplant and postemergence

herbicide systems in Wyoming sugarbeet. J. Am. Soc. Sugar Beet Technol.
3411-19.

14

Morishita, D. W. and R. W. Downard. 1995. Weed control in sugar beets with
triflusulfuron as influenced by herbicide combination, timing, and rate. J. Am.
Soc. Sugar Beet Technol. 32:23-35.

Nord, C. A., C. G. Messersmith, and J. D. Nalewaja. 1999. Growth of Kochia scoparia,
Salsola iberica, and Triticum aestivum varies with temperature. Weed Sci.
47:435-439.

Oryokot, J. O. E., S. D. Murphy, A. G. Thomas, and C. J. Swanton. 1997. Temperature-
and moisture-dependent models of seed germination and shoot elongation in
green and redroot pigweed (Amaranthus powellii, A. retroflexus). Weed Sci.
45:488-496.

Renner, K. A., and G. E. Powell. 1991. Velvetleaf (Abutilon theophrastr) control in
sugarbeet (Beta vulgaris). Weed Technol. 5:97-102.

Roman, E. S., A. G. Thomas, S. D. Murphy, and C. J. Swanton. 1999. Modeling
germination and seedling elongation of common lambsquarters (Chenopodium
album). Weed Sci. 47:149-155.

Roman, E. S., S. D. Murphy, and C. J. Swanton. 2000. Simulation of Chenopodium
album seedling emergence. Weed Sci. 48:217-224.

Schweizer, E. E. 1973. Predicting sugarbeet root losses based on kochia densities.
Weed Sci. 21:565-567.

Schweizer, E. E. 1983. Common lambsquarters (Chenopodium album) interference in
sugarbeets (Beta vulgaris). Weed Sci. 31 :5-8.

Schweizer E. E. and A. G. Dexter 1987. Weed control in sugarbeets (Beta vulgaris) in
North America. Rev. Weed Sci. 1987. 3:113-133

Schweizer, E. E. and L. D. Bridge. 1982. Sunflower (Helianthus annuus) and velvetleaf
(Abutilon theophrastr) interference in sugarbeets (Beta vulgaris). Weed Sci.
30:514-519.

Schweizer, E. E. and T. C. Lauridson. 1985. Powell amaranth (Amaranthus powellir)
interference in sugarbeet (Beta vulgan's). Weed Sci. 33:518-520.

Smith, G. A., and E. E. Schweizer. 1983. Cultivar X herbicide interaction in sugarbeet.
Crop Sci. 23:325-328.

Starke, R. J. and K. A. Renner. 1996. Velvetleaf (Abutilon theophrastr) and sugarbeet
(Beta vulgaris) response to triflusulfuron and desmedipham plus phenmedipham.
Weed Technol. 121-126.

Sullivan, E. F., R. L. Abrams, and R. R. Wood. 1963. Weed control in sugar beets by
combinations of thiolcarbamate herbicides. Weeds 11:258-260.

Vencill, W. K. 2002. Herbicide Handbook. 8th ed. Lawrence, KS: Weed Science Society
of America. 91 p.

15

Vinocur, M. G. and J. T. Ritchie. 2001. Maize leaf development biases caused by air-
apex temperature differences. Agron. J. 93:767-772.

Warner, J. D. 1996. Adjuvant effect on weed control in sugarbeet. M. S. thesis, N. D.
State Univ., Fargo.

Warren, L. E. 1954. The control of annual grasses in sugar beets with dalapon. Proc.
Am. Soc. Sugar Beet Technol. 82124-129.

Wilson, R. G. 1994. New herbicides for postemergence application in sugarbeet (Beta
vulgaris) Weed Technol. 8:807-811.

Wilson, R. G. 1999. Response of nine sugarbeet (Beta vulgaris) cultivars to
postemergence herbicide applications. Weed Technol. 13:25-29.

Wilson, R. G., D. Yonts, and J. A. Smith. 2002. Influence of glyphosate and glufosinate

on weed control and sugarbeet (Beta vulgaris) yield in herbicide-tolerant
sugarbeet. Weed Technol. 16:66-73.

16

CHAPTER 2

TIMING OF POSTEMERGENCE MICRO-RATE APPLICATIONS BASED ON
GROWING DEGREE DAYS IN SUGARBEET (Beta vulgaris)

Abstract. Postemergence (POST) herbicides must be applied in sugarbeet when
weeds are less than 2.5 cm in height for effective weed control. Weeds continue to
emerge during the season so multiple POST applications are usually required. This
research was conducted to determine if growing degree days (GDD) could be used to
effectively time postemergence herbicide applications. GDD were calculated using the
average daily temperature with a base temperature of 1.1 C. Common lambsquarters
and redroot pigweed were grown in the growth chamber and treated with three micro-
rate herbicide applications spaced every 97, 125, and 152 GDD with a base of 1.1 C.
Common lambsquarters was controlled with all treatments, but redroot pigweed control
in the 152 GDD (C) timing was reduced compared to the 97 GDD and 125 GDD (C)
timings. ln field research, the sugarbeet varieties Hilleshog E-17 and Beta 5400 were
planted April 3, April 17, and May 3 in 2001 and April 5, April 17, and May 1 in 2002.
Micro-rate applications (desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ai/ha
plus triflusulfuron at 0.004 kg ai/ha plus clopyralid at 0.023 kg aelha plus methylated
seed oil (MSO) at 1.5% v/v) were applied (a) every 7 d, (b) as needed, (0) every leaf pair
(2001 only), (d) every 97 GDD, (e) every 125 GDD (2002 only) and (e) every 152 GDD.
All herbicide timings controlled common lambsquarters 92% or greater in both 2001 and
2002. In 2001, Amaranthus spp. control was 91% with the 152 GDD timing compared to
97% with the 7 d timing, and in 2002 control ranged from 80% with the 152 GDD timing
to 86% with the 7 d timing. Although Amaranthus spp. control was somewhat less when
the micro-rate treatment was applied on a 152 GDD timing, recoverable sucrose in 2001
was significantly greater with the 152 GDD timing at 7,748 kg/ha compared to 6,691

kg/ha with the 7 d timing. In 2002, recoverable sucrose was significantly greater with the

17

152 GDD timing at 4,935 kg/ha compared to 4,261 kg/ha with the 7 d timing. When the
micro-rate herbicide treatment was applied every 152 GDD, the total number of
applications was reduced by two in 2001 and three on 2002 compared to the 7 day or
labeled timing for the early and mid-April planting dates. For the early May planting
dates, the total micro-rate applications were reduced by two in both 2001 and 2002 with
the 152 GDD timing compared to the 7 d timing. Sugarbeet growers are continuously
trying to reduce production costs in a competitive market and timing micro-rates by GDD

may reduce herbicide input costs.

Nomenclature: desmedipham; phenmedipham; ethofumesate; triflusulfuron; clopyralid;
common lambsquarters, Chenopodium album L. #1 CHEAL; redroot pigweed,
Amaranthus retroflexus L. # AMARE; pigweed species, Amaranthus retroflexus and
Amaranthus powellii S. Wats. # AMASS; sugarbeet, Beta vulgaris L. Hilleshog E17 and
Beta 5400.

Abbreviations: GDD, growing degree days, POST, postemergence PRE,

preemergence.

 

1 Letters following this symbol are a WSSA-approved computer code from Composite List of
Weeds, Revised 1989. Available only on computer disk from WSSA, 810 East 10th Street,
Lawrence, KS 66044-8897.

18

INTRODUCTION

In the last five years, weed control has changed from conventional
preemergence (PRE) and POST herbicides to the use of transgenic crops primarily
resistant to glyphosate and glufosinate. The use of non-selective herbicides such as
glyphosate or glufosinate provides a greater application window with respect to weed
size, because these herbicides can be applied to larger weeds than conventional
herbicides and still provide excellent weed control. Glyphosate and glufosinate resistant
sugarbeet are currently registered for use, but the sugar companies will not accept
genetically modified sugarbeet because of the marketing problems associated with
sucrose from genetically modified sugar. Sugarcane growers could have a sugar
marketing advantage in the world market because of the European markets
unwillingness to accept genetically modified crops.

In contrast to the very effective non-selective herbicides glyphosate and
glufosinate, POST sugarbeet herbicides seldom control weeds larger than two-true
leaves. Application timing is critical for adequate weed control. The micro-rate (a
combination of desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha or
desmedipham plus phenmedipham plus ethofumesate (1 :1 :1 ratio) at 0.09 kg ailha plus
triflusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg aelha plus methylated seed oil
(MSO) at 1.5% v/v) is usually applied POST three- to- five times to young actively
growing weeds at the cotyledon growth stage. The need for additional treatments is
affected by the continuing germination of weed seeds and the level of control achieved
by the previous treatment. Weeds not controlled by micro-rate treatments may be
controlled with higher herbicide rates applied twice and often referred to as a standard-
split, or by hand labor. Growers apply standard-split applications in a band and cultivate
between the rows to reduce the cost of these POST herbicides. Also hand labor has

become more expensive due to increased government regulations and a decrease in the

19

available work force. Schweizer and Dexter (1987) reported a doubling in hand labor
costs from $41/ha in 1970 to $82lha in 1986. A second weeding cost $26/ha in 1970
versus $54/ha in 1986. Both standard-splits and hand-labor are more costly than
broadcast applying the micro-rate four times so many growers try to avoid these
practices. Scouting fields for weeds less than 2 cm in size is difficult and time
consuming. Therefore growers base POST herbicide applications on calendar days to
minimize scouting. The ability to predict the proper timing of herbicide treatments to
Optimize weed control and minimize sugarbeet injury and herbicide cost would be a
major benefit to the sugarbeet grower.

The use of growing degree days (GDD) to predict plant development has been
used successfully for various crops (Vinocur and Ritchie 2001, Juskiw et al. 2001) and
weeds (Nord et al. 1999, Ball et al. 1995). These GDD systems are based on air
temperature. Many researchers have tried to predict weed seed germination and
emergence based on soil temperature and soil moisture (Roman et al. 2000, Oryokot et
al. 1997, Harvey and Forcella 1993, Forcella 1993). In controlled environments, the
temperature and rate of emergence of many weeds has been determined. However,
this research predicts the time of 50% germination or weed emergence (Oryokot et al.
1997, Harvey and Forcella 1993, Alm et al.1993). ln field conditions, when weeds have
reached 50% emergence the timing is probably too late for the micro-rate, because a
certain percentage of the weeds would exceed the size controlled by the micro-rate.
Roman at al. (2000) stated that the use of soil temperature to calculate GDD was a
better predictor of common lambsquarters (Chenopodium album L.) seedling emergence
than air temperatures. However, this was only true at one of the two locations in one of
the two years, and only under no-till conditions. Most of the sugarbeets grown in the
US. are planted in fields that have either been chisel plowed or moldboard plowed the

previous fall. Although significant research has been conducted using GDD to time

20

pesticide applications in many crops, particularly insecticide treatments, GDD have not
been used to schedule multiple POST herbicide treatments such as those used in
sugarbeet.

Currently the herbicide label states that the first micro-rate treatment should be
applied when weeds are at the cotyledon growth stage, and follow up treatments should
be applied every 5 to 7 d as required. This 5 to 7 d interval is often too short, but can
also be too long depending on environmental conditions between treatments. Moisture
is required for weed germination and growth. Furthermore, weeds emerge and grow
more rapidly under warm conditions. Improper timing with the micro-rate may result in
poor weed control, sugarbeet injury, and/or undue cost.

The objectives of this research were to determine if sequential POST herbicide
applications in sugarbeet could be based on GDD, and to determine if weed control
would be equal to or greater than POST applications based on calendar days. POST
herbicide applications based on GDD could increase weed control, reduce herbicide
applications, and reduce crop injury. Better timing of POST herbicides in sugarbeet may

result in greater sucrose production and increased net returns.

21

MATERIALS AND METHODS
Growth Chamber Studies. Common lambsquarters and redroot pigweed (Amaranthus
retroflexus L.) (Source: Michigan State University Agronomy Farm, East Lansing) were
planted in plastic pots (10-cm by 15-cm depth) filled with a mixture of sphagnum peat
and perlite. Pots were placed in a growth chamber at 27:11 C (dayznight temperature)
for 5 d and were transferred to growth chambers set at 23:7, 27:11, and 31 :15 C 2 d
prior to the first micro-rate treatment. The 23:7 C chamber provided 97 GDD every 7 d,
the 27:11 C chamber provided 125 GDD every 7 d, and the 31:15 C chamber provided
152 GDD every 7 d. GDD were calculated using the average daily temperature and the
base temperature was 1.1 C (max + min/2 -1.1 C = GDD in C for 1 day). Holen and
Dexter (1996) reported that 1.1 C was the optimum base temperature for sugarbeet. All
chambers had a photoperiod of 16:8 h (lightzdark). Pots were watered daily as needed
and fertilized once each week with 50 ml of N, P205, K20 (20:20:20) at 20 ppm
concentration. The experimental design was a RCB with four replicates and was
repeated. The whole-plot was the three growth chamber temperatures, and the sub-plot
was herbicide treatment. Treatments included (a) no treatment, (b) herbicide treatments
applied two times starting two wk after planting, and (c) herbicide treatments applied
three times starting one wk after planting within each growth chamber. Data were
subjected to ANOVA using the PROC MIXED procedure in SAS and means were
separated using Fishers Protected LSD at (P 0.05). The herbicides applied in the
micro-rate each application were desmedipham plus phenmedipham at 0.09 kg/ha plus
triflusulfuron at 0.004 kg/ha plus clopyralid at 0.023 kg/ha plus M802 at 1.5% v/v.
Herbicides were applied two (herbicide applications 14 and 21 days after planting) or
three times (herbicide applications 7, 14, and 21 days after planting) on weekly intervals

which resulted in spray schedules of 97, 125, and 152 GDD. Herbicide treatments were

22

applied with a single tip track-sprayer equipped with an 8003E3 spray tip calibrated to
deliver 187 L - ha’1 at 207 kPa. Visual observations were recorded 1 wk after the last
treatment.

Field Studies. Field experiments were conducted in 2001 and 2002 near East Lansing,
MI. The experiments were located in different fields each year on a Colwood-Brookston
loam (fine-loamy, mixed, mesic Typic Haplaquolls, and fine-loamy, mixed, mesic Typic
Argiaqoulls), 53% sand, 27% silt, and 21% clay, with pH 6.9 and 2.4% organic matter.
Fields were fall plowed followed by a field cultivator in the spring for seedbed
preparation. Prior to planting sugarbeet, the fields were fertilized with granular urea (46-
0-0) at 125 kglha using a broadcast applicator and incorporated to a 10-cm depth with a
field cultivator. In addition, granular fertilizer N, P205, K20 (19-19-19) at 110 kglha was
applied in-furrow at planting. Both Hilleshog E-17‘ and Beta 54005 were seeded at a
depth of 2.5 cm at 118,000 seeds/ha in 76 cm rows with a John Deere 7200 Max-
Emerge® 26 planter. Sugarbeets were planted to stand with a seed spacing of 250
sugarbeet per 30 m of row. Planting dates in 2001 were April 5, April 17, and May 3; in
2002 the planting dates were April 7, April 17, and May 1. Micro-rate treatments in 2001
and 2002 were applied (a) every 7 d, (b) as needed, (c) every leaf pair (2001 only), (d)
every 97 GDD, (e) every 152 GDD (2002 only), and (f) every 152 GDD. The leaf pair
treatment was dropped in 2002 because of the difficulty in determining “leaf pair” in a
sugarbeet population and the fact that the 2001 field research and growth chamber
research indicated that 125 GDD would be a proper substitution. GDD were calculated
using the average daily temperature with a base of 1.1 C. Herbicide treatments were

applied using a tractor mounted compressed air sprayer in water at 187 L ha'1 207 kPa

 

2 Loveland industries Inc., PO Box 1289, Greeley, CO 80632.

3 Teejet even fan tips. Spraying Systems Co., North Ave. and Schmale Road, Wheaton, IL 60188.
‘ Hilleshog seeds, 1350 Kansas Ave., Longmount, CO 80501.

5 Beta seeds, 1788 Maschall Road, Shakopee, MN 55379.

23

through XR 80037 spray tips. All herbicide treatments were initiated when average weed
height was 1.5 cm, and repeated according to treatment. In 2002, clethodim ((E,E)-(:I:)-
2-[1 -[[(3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-
cyclohexen-I-one) was applied over the entire plot area to control giant foxtail, but was
not needed in 2001.

Sugarbeet injury and weed control were estimated visually 14 days after the final
herbicide treatment for each planting date using the rating scale of 0 (no injury) to 100
(completely killed). Sugarbeet was topped with a two-row topper, and harvested
October 30, 2001 and October 21, 2002 with a mechanical two-row lifter. A sample from
each plot was analyzed for recoverable sucrose by the method outlined by the
Association of Official Agriculture Chemists (1955) by Michigan Sugar Company,
Carollton, MI.

The experimental design was a factorial in a split-split-plot arrangement with four
replicates. The whole-plot was planting date, sub-plot was sugarbeet variety,
and sub-sub-plot was the various herbicide treatments. Data were subjected to ANOVA
using the PROC MIXED procedure in SAS and means were separated using Fishers
Protected LSD at (P 0.05). Planting date by variety and treatment by variety by
planting date interactions were not significant; therefore, the data were combined over

varieties and planting dates for the analyses.

 

6 Deere and Co., 501 River Drive, Moline, IL 61265-1100.
7 Teejet fiat fan tips. Spraying Systems Co., North Ave. and Schmale Road, Wheaton, IL 60188.

24

RESULTS AND DISCUSSION
Growth chamber studies. Common lambsquarters and redroot pigweed control was
90% or more when the micro-rate herbicide treatment was applied three times spaced
every 97 or 125 GDD (Table 2). However, when the micro-rate treatment was applied
three times spaced every 152 GDD, common lambsquarters and redroot pigweed
control decreased to 84 and 63%, respectively. When the first application was skipped,
common lambsquarters and redroot pigweed control was reduced for both the 125 and

152 GDD timings. Waiting until GDD totaled 250 resulted in larger weeds that could not
be controlled by the micro-rate of these herbicides, even when a second application was
made 7 d later. This research showed that micro-rates of herbicides applied three times
starting one wk after planting using the 97 and 125 GDD timing effectively controlled
common lambsquarters and redroot pigweed. Furthermore, the timeliness of the first
application is apparent. If weeds “escape” the first treatment and exceed 3 cm, control
decreases to 87% or less. The development of common lambsquarters was likely
reduced in the 31:15 C growth chamber because optimum growth occurs at 25 C, and
growth decreases at higher temperatures. This would explain the complete control
observed with the 152 GDD spacing in the growth chamber, but reduced control
observed in the field in 2002 (Table 7).

POST micro-rate applications In the field In 2001 and 2002. When the micro-rate
was applied every 152 GDD, the total number of applications was reduced by two in
2001 and three in 2002 compared to the 7 d or labeled timing for the early and mid-April
planting dates (Table 3 and Table 4). For the early May planting dates, total micro-rate
applications were reduced by two with the 152 GDD timing compared to the 7 d timing in
both 2001 and 2002 (Table 5). The mean number of days between herbicide
applications was 4.5 d greater for the 152 GDD timing for all planting dates in 2001 and

2002, and was 4 d greater for the 125 GDD timing in the early and late planting dates in

25

2002 compared to the 7 d timing (Tables 3, 4,and 5). This lengthening of the time
interval between applications reduces costs and is an advantage to the sugarbeet
grower if weeds are controlled.

Sugarbeet response In the field in 2001 and 2002. The sugarbeet variety Beta 5400
tended to incur greater injury than Hilleshog E-17 (personal observation), but the varietal
differences were not significant and the data were combined. Sugarbeet injury ranged
from 18% in the 152 GDD timing to 27% in the 7 d timing in 2001, and from 19% to 29%
in 2002, respectively (Table 6). Sugarbeet injury was evaluated as an overall reduction
in leaf area and stunted sugarbeet growth. In 2001, sugarbeet injury was less in the 152
GDD timing compared to the 7 d timing, and in 2002 injury in the 7 d timing was greater
than all other timings. Sucrose yield was greater in sugarbeets that were treated with a
micro-rate every 152 GDD and every new leaf pair compared to the every 7 d and “as
needed’ timings in 2001 (Table 6). In 2002, sucrose yield was significantly less in
sugarbeets in the 7 d timing than in all other timings. Extending the time between micro-
rate herbicide applications from 7.4 to 10.6 d or longer (Table 3) allowed sugarbeet to
metabolize the herbicides and increase leaf expansion (Hendrick et al. 1974).

Weed response. Both common lambsquarters and Amaranthus spp. populations were
high in all plots (550 per m2). Other weeds that were present sporadically were common
ragweed (Ambrosia artemisiifolia L.), eastern black nightshade (Solanum ptycanthum
Dunn.), and giant foxtail (Setaria faben' Herrm.). Common lambsquarters control was
excellent with all timings in both years; with the exception of minor differences in 2002
(Table 7). In 2002, common lambsquarters control was less in the 152 GDD timing
compared to the 7 d, as needed, and 97 GDD timings, but similar to the 125 GDD timing.
Control of Amaranthus spp. (mixture of redroot pigweed and powell amaranth) was
greater in the 7 (1, leaf pair, and 97 GDD timings than in the as needed and 152 GDD

timing in 2001; however, control was greater than 90% in all timings. Amaranthus spp.

26

control in 2002 did not differ by herbicide timing. In 2002, Amaranthus spp. control was
generally less than in 2001. The reduced Amaranthus spp. control may have been
caused by the moisture deficit experienced at East Lansing, Michigan in 2002 (Table 1).
Horak and Wax (1991) reported that reduced soil moisture delays redroot pigweed
germination. This also explains why more herbicide treatments had to be applied in
2002 than 2001. Redroot pigweed generally germinates when temperatures exceed 25
C, whereas common lambsquarters generally emerges when temperatures exceed 10
C. Orykot et al. (1997) reported that redroot pigweed emerges from 19 to 33 C. Harvey
and Forcella (1993) reported that common lambsquarters emerges from 9 to 33 C;
however, the optimum temperature was 24 C.

Weed control was reduced when the time between micro-rate applications was
extended, or as total applications decreased. However, weed control was acceptable
with the 152 GDD timing in both 2001 and 2002, and sucrose yield was similar or greater
in the 152 GDD timing compared to other timings. The cost of one micro-rate application
was approximately $50/ha, not including application cost in 2002. By applying the micro-
rate using GDD, two or three micro-rate applications could be eliminated while
maintaining sucrose yields similar to, or greater, than the 7 d timing. Sugarbeet growers
would save up to $150/ha in herbicide expense when using GDD to time micro-rate
applications compared to the 7 d timing. This cost is even greater when considering
other factors such as sugarbeet injury, compaction, equipment depreciation, and labor
costs.

A model based on soil temperature and moisture that would provide consistent
results from field to field may not be feasible because of differences in tillage practices,
soil texture, soil type, moisture, burial depth, and the high genetic diversity of weed
seeds influencing weed seed emergence. In addition, soil temperature data are often

not as readily accessible as air temperature, and growers use GDD based on air

27

temperature for other pest management decisions for crops including com, soybeans,
and sugarbeet. The time spent in calculating GDD is minimal. Weather stations and the
sugar companies provide maximum and minimum temperatures each day. Extensive
scouting is not required because redroot pigweed and common lambsquarters are
currently the two important weed species in sugarbeet production. Other weeds such as
common ragweed are easily controlled with clopyralid regardless of size and annual
grasses are controlled with acetyI-CoA carboxylase (ACCase) inhibiting herbicides such
as Sethoxydim, clethodim, and quizalofop (Vencill 2002). Velvetleaf is controlled by the
micro-rate since triflusulfuron requires a MSO for effective control (Starke and Renner
1991 ). Therefore, timing POST herbicide applications by GDD in sugarbeet will control a
broadspectrum of weeds and increase growers/applicators confidence in the timeliness

of POST herbicide applications.

28

LITERATURE CITED

Alm, D. M., E. W. Stoller, and L. M. Wax. 1993. An index model for predicting seed
germination and emergence rates. Weed Technol. 7:560-569.

Association of Official Agriculture Chemists. 1955. Official methods of analysis. 8th ed.
Washington, DC. pp. 564-568.

Ball, D. A.., B. Klepper, and D. J. Rydrych. 1995. Comparative above-ground
development rates for several annual grass weeds and cereal grains. Weed Sci.
43:41 0-41 6.

Brimhall, P. B., E. W. Chamberlain, and H. P. Alley. 1965. Competition of annual weeds
in sugarbeets. Weeds 13:33-35.

Dawson, J. H. 1965. Competition between irrigated sugarbeets and annual weeds.
Weeds 13:245-249.

Dexter, A. G. and J. L. Luecke. 2000. Survey of weed control and production practices
on sugarbeet in eastern North Dakota and Minnesota. Sugarbeet Res. Ext. Rep.
30:36.

Dexter, A. G. 2000. Weed control guide for sugarbeet. Sugarbeet Res. Ext. Rep. 30:3.

Dexter, A. G. and J. L. Luecke. 2001. Survey of weed control and production practices
on sugarbeet in eastern North Dakota and Minnesota. Sugarbeet Res. Ext. Rep.
31 :36.

Forcella, F. 1993. Seedling emergence model for velvetleaf. Agron. J. 85:929-933.

Harvey, S. J., and F. Forcella. 1993. Vernal seedling emergence model for
lambsquarters (Chenopodium album). Weed Sci. 41 :309-316.

Hendrick, L. W., W. F. Meggitt, and D. Penner. 1974. Basis of selectivity of
phenmedipham and desmedipham on wild mustard, redroot pigweed, and sugar
beet. Weed Science. 22:179-184.

Holen, C. D. and A. G. Dexter. 1996. A growing degree day equation for early sugarbeet
leaf stages. Sugarbeet Res. Ext. Rep. 27:152-157.

Horak, M. J. and L. M. Wax. 1991. Germination and seedling development of bigroot
momingglory (Ipomea pandurata). Weed Sci. 39:390-396.

Juskiw, P. E., Y. W. Jame, and L. Kryzanowski. 2001. Phenological development of
spring barley in a short-season growing area. Agron. J. 93:370-379.

Nord, C. A., C. G. Messersmith, and J. D. Nalewaja. 1999. Growth of Kochia scoparia,

Salsola iberica, and Triticum aestivum varies with temperature. Weed Sci.
47:435-439.

29

Oryokot, J. O. E., S. D. Murphy, A. G. Thomas, and C. J. Swanton. 1997. Temperature-
and moisture-dependent models of seed germination and shoot elongation in
green and redroot pigweed (Amaranthus powellii, A. retroflexus). Weed Sci.
45:488-496.

Roman, E. S., S. D. Murphy, and C. J. Swanton. 2000. Simulation of Chenopodium
album seedling emergence. Weed Sci. 48:217-224.

Starke, R. J. and K. A. Renner. 1996. Velvetleaf (Abutilon theophrastr) and sugarbeet
(Beta vulgaris) response to triflusulfuron and desmedipham plus phenmedipham.
Weed Technol. 121-126.

Vencill, W. K. 2002. Herbicide Handbook. 8th ed. Lawrence, KS: Weed Science Society
of America. p. 62, 260, 266.

Vinocur, M. G., and J. T. Ritchie. 2001. Maize leaf development biases caused by air-
apex temperature differences. Agron. J. 93:767-772.

Warner, J. D. 1996. Adjuvant effect on weed control in sugarbeet. M. S. thesis, N. D.
State Univ., Fargo. pp. 28

Wicks, G. H., and R. G. Wilson. 1983. Control of weeds in sugarbeets (Beta vulgaris)
with hand hoeing and herbicides. Weed Sci. 31:493-499.

30

Table 1. Deviations from the normal monthly precipitation and mean temperature in
2001 and 2002 at Michigan State University Horticulture Teaching and Research Center,

East Lansing, MI.

 

 

 

Precipitation Temperature
(cm) (C)
Month 2001 2002 2001 2002
April 0.4 1.3 0.6 -1.4
May 13.2 5.2 1.7 -2.9
June 05 -3.6 0.1 1.0
July -5.3 1.8 -0.3 1.2
August -3.8 -3.9 1.1 0.5
September 3.8 -5.8 -1.5 1.9

 

31

Table 2. Common lambsquarters and redroot pigweed control 28 days after planting
with two or three POST herbicide treatments applied every 97, 125, and 152 growing

degree days (in C) in growth chambers.

 

 

Temperature Herbicide Common Redroot
regimes‘iI GDD applicationsb lambsquarters pigweed
Dayznight (C) (C) DAP" ——————- % controla

23:7 97 14 and 21 100a 100a
23:7 97 7, 14, and 21 100a 100a
27:11 125 14 and 21 87c 77c
27:11 125 7, 14, and 21 95b 90b
31 :15 152 14 and 21 52d 34e
31:15 152 7, 14, and 21 84c 63d

 

aCommon lambsquarters and redroot pigweed were grown in growth chambers set at
23:7 C, 27:11 O, and 31 :15 C. Growing degree days were calculated by subtracting 1.1
C from the average daily temperature (C).

bHerbicide treatments were applied 14 and 21 d after planting or 7, 14, and 21 d after
planting. Herbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09
kg ailha plus triflusulfuron at 0.004 kg ai/ha plus clopyralid at 0.023 kg aelha and
methylated seed oil at 1.5% v/v.

°Abbreviationsz GDD, growing degree days, DAP, days after planting.

dMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

32

Table 3. The number of days after planting that micro-rate herbicide treatments were

applied for the April 5, 2001 and April 7, 2002 planting dates“.

 

 

 

 

Timings
2001 2002
Leaf 97 152 97 125 152
7 day Scout pair GDD GDD 7 day Scout GDD GDD GDD
21 21 21 21 21 9 9 9 9 9

27 27 29 29 33 16 24 24 24 29
38 45 38 38 45 24 37 37 37 44

45 55 45 45 59 29 51 51 55 55

 

 

51 55 55 69 37 61 57 61 61
60 67 64 43 68 69 73 73
67 70 51 73 73 79
61
68
Meanc 7.3 11.3 9.2 8.2 12 7.4 10.6 10.6 11.6 12.8
Total“ 7 4 6 7 5 9 7 7 7 6

 

a Growing degree days were calculated by subtracting 1.1 C from the average daily
temperature (C).

bTimings included: every 7 d (labeled treatment), as needed (scouting for weeds at
cotyledon growth stage), every leaf pair (application every new leaf pair in sugarbeet),
every 97 GDD, every 125 GDD, and every 152 GDD.

°Mean is the average number of days between herbicide applications.

dTotal is the total number of applications for each herbicide timing.

33

Table 4. The number of days after planting that micro-rate herbicide treatments were

applied for the April 19, 2001 and April 17, 2002 planting dates”.

 

TimintsL
2001 2002

 

Leaf 97 152 97 125 152
7daL Scout pair GDD GDD 7day Scout GDD GDD GDD

1 5 15 15 15 15 19 19 19 19 19
21 26 26 21 27 27 27 33 34 37
26 39 33 27 39 33 41 45 45 51
33 57 43 33 55 41 51 54 54 63

39 66 52 43 67 51 58 63 63 66

 

 

48 72 67 52 58 63 66 69
55 73 58 66 69 72
67 72
MeanC 6.7 11.4 9.7 7.4 13 7.6 8.3 8.8 10 14.3
Total6 7 6 7 8 5 8 7 7 6 5

 

a Growing degree days were calculated by subtracting 1.1 C from the average daily
temperature (C).

t’Timings included: every 7 d (labeled treatment), as needed (scouting for weeds at
cotyledon growth stage), every leaf pair (application every new leaf pair in sugarbeet),
every 97 GDD, every 125 GOD, and every 152 GDD.

cMean is the average number of days between herbicide applications.

dTotal is the total number of applications for each herbicide timing.

34

Table 5. The number of days after planting that micro-rate herbicide treatments were

applied for the May 2, 2001 and May 3, 2002 planting dates”.

 

Timings

 

2001 2002

 

Leaf 97 1 52 97 125 1 52
7day Scout pair GDD GDD 7day Scout GDD GDD GDD

1 1 1 1 1 1 1 1 1 1 13 13 13 13 13
17 23 17 17 21 19 27 27 31 31
23 36 32 27 38 27 44 40 40 44
32 51 39 36 51 37 49 49 49 52

39 57 51 42 60 43 55 55 58 61

 

 

51 57 49 51

57 55 57
Meanc 7.7 11.5 9.2 7.7 12.3 7.5 10.5 10.5 11.3 12
Totald 7 5 6 7 5 7 5 5 5 5

 

a Growing degree days were calculated by subtracting 1.1 C from the average daily
temperature (C).

bTimings included: every 7 d (labeled treatment), as needed (scouting for weeds at
cotyledon growth stage), every leaf pair (application every new leaf pair in sugarbeet),
every 97 GDD, every 125 GOD, and every 152 GDD.

°Mean is the average number of days between herbicide applications.

dTotal is the total number of applications for each herbicide timing.

35

Table 6. Sugarbeet injury and yield as affected by herbicide application timings in 2001

and 2002, averaged over varieties and planting dates“.

 

 

 

 

 

Sugarbeet injury Sucrose yield

Timing" 2001 2002 2001 2002
% RWSH

7 d 27a 29a 6,691 b 4,261 b
As needed 23ab 18b 6,612b 4,700a
Leaf pair 24ab - 7,493a -
97 GDD 23ab 18b 7,131 ab 4,890a
125 GDD - 20b - 4,7103
152 GDD 18b 19b 7,748a 4,935a

 

aMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

bThe leaf pair treatment was replaced with the 125 growing degree day treatment in
2002.

°Abbreviationsz RWSH, recoverable white sucrose per ha.

dSugarbeet injury was recorded 14 days after the last herbicide application for each
planting date.

°Herbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha
plus triflusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg aelha and methylated
seed oil at 1.5% v/v.

36

Table 7. Common lambsquarters and Amaranthus species control by herbicide

applications timings in 2001 and 2002, averaged over varieties and planting dates“.

 

 

 

 

 

Common Amaranthus
lambsquarters species“
Timingc 2001 2002 2001 2002
%

7 d 97a 96ab 97a 86a
As needed 99a 96ab 86c 83a
Leaf pair 99a - 963 -
97 GDD 100a 96ab 99a 84a
125 GDD - 93bc - 83a
152 GDD 97a 92c 91 b 80a

 

" Sugarbeet injury was recorded 14 days after the last herbicide application for each
planting date.

Means within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.
cHerbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha
plus triflusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg aelha and methylated
seed oil at 1.5% v/v.
dAmaranthus species was a combination of redroot pigweed and powell amaranth.

37

CHAPTER 3

EFFECT OF PREEMERGENCE AND POSTEMERGENCE HERBICIDES ON WEED
CONTROL AND SUGARBEET (Beta vulgaris) YIELD AND QUALITY.

Abstract. Weed control in sugarbeet is very expensive, and often inCludes
peemergence (PRE) and postemergence (POST) herbicides, cultivation, and hand labor.
In 2000 the “micro-rate”, a combination of desmedipham plus phenmedipham (1 :1 ratio)
at 0.09 kg ailha or desmedipham plus phenmedipham plus ethofumesate (1 :1 :1 ratio) at
0.09 kg ailha plus triflusulfuron at 0.004 kg ailha plus Clopyralid at 0.023 kg aelha plus
1.5% methylated seed oil (MSO), received registration in Michigan. The micro-rate
herbicide treatment is applied three to five times on a 7 d interval. Some growers have
reported more injury from micro-rate applications than standard applications. This
research evaluated weed control, sugarbeet injury and yield in sugarbeet treated with
various herbicide programs including PRE only, POST only, and combinations of PRE
and POST herbicides. Common lambsquarters control was 91 to 95% with all POST
treatments in 2001, and 97% or greater with all POST treatments when combined over
PRE treatments. In 2002, desmedipham plus phenmedipham at 0.09 kglha plus
triflusulfuron at 0.004 kglha plus Clopyralid at 0.023 kglha plus 1.5% M80 and
desmedipham plus phenmedipham plus ethofumesate at 0.27 kglha plus triflusulfuron at
0.017 kglha plus clopyralid at 0.1 kglha provided 90 and 100% control, respectively.
Amaranthus spp. control was 86 to 92% in 2001, and 96 to 100% in 2002 with all POST
treatments. In 2001, Amaranthus spp. control was 93 to 96%, and 97 to 100% with all
POST treatments when combined over PRE treatments. Sugarbeet injury was similar
among all herbicide treatments in 2001. In 2002, sugarbeet injury ranged from 29 to
38% when both desmedipham plus phenmedipham or desmedipham plus
phenmedipham plus ethofumesate were applied at 0.09 kglha compared to 43% when

desmedipham plus phenmedipham or desmedipham plus phenmedipham plus

38

ethofumesate were applied at 0.56 and 0.27 kglha, respectively. Recoverable sucrose
yields did not differ among all herbicide treatments in the small plot and in the strip plots

in sugarbeet growers’ fields in 2001 and 2002.

Nomenclature: desmedipham; phenmedipham; ethofumesate; triflusulfuron; clopyralid;
common lambsquarters, Chenopodium album L. #1 CHEAL; redroot pigweed,
Amaranthus retroflexus L. # AMARE; pigweed species, Amaranthus retroflexus and
Amaranthus powellii S. Wats. # AMASS; sugarbeet, Beta vulgaris L.

Additional index words: Micro-rate, standard-split.

Abbreviations: PRE, preemergence, POST, postemergence, PPI, preplant

incorporated, MSO, methylated seed oil.

 

‘ Letters following this symbol are a WSSA-approved computer code from Composite List of
Weeds, Revised 1989. Available only on computer disk from WSSA, 810 East 10th Street,
Lawrence, KS 66044-8897.

39

INTRODUCTION

Weed control in sugarbeets has relied on both PRE and POST herbicide
applications. Cycloate can be pre-plant incorporated (PPI) or pyrazon and ethofumesate
applied PRE to provide residual weed control. Two major limiting factors affecting the
use of PRE herbicides are the excessive cost which restricts their overall use and
requires that they be applied in a band application, and the requirement of moisture to
provide adequate activation of the PRE herbicides. Renner and Powell (1991) reported
inconsistent weed control from PRE herbicides among years. In addition, previous
research has reported that sugarbeet treated with soil applied herbicides were more
susceptible to POST herbicide treatments (Dexter and Luecke 1988, Smith et al. 1982).
However, Starke and Renner (1996) reported that sugarbeet response to POST
herbicides was not affected by PPl or PRE herbicide treatments. POST herbicides such
as desmedipham plus phenmedipham (1 :1 ratio) plus triflusulfuron plus clopyralid are
almost always applied to control weeds not controlled by the PRE herbicides.

Since the eaIIy 19705, research on reduced rates of POST herbicides applied
twice as a split application has resulted in better weed control. Desmedipham applied at
0.28 kglha followed by (fb) 0.28 kglha 7 to 14 d later, controlled weeds more effectively
and tended to injure sugarbeet (Beta vulgaris L.) less than desmedipham at 1.12 kglha
or split applications of 0.56 kglha fb 0.56 kglha (Dexter 1994). Split applications of
desmedipham at 0.28 fb 0.28 kglha were widely used by 1980. From 1984 to 1998,
96% of the sugarbeet he no longer received a PRE herbicide, and growers switched to a
POST only program relying on two to three standard-split treatments and one to two
cultivations in North Dakota and Minnesota (Luecke and Dexter 2003). In 1998 the
micro-rate (desmedipham at 0.09 kglha plus triflusulfuron at 0.004 kglha plus clopyralid
at 0.03 kglha plus MSO at 1.5% v/v) was registered in North Dakota and Minnesota, and

was registered in Michigan in 2000.

40

The switch to a total POST program in Michigan has occurred at a slower rate
than North Dakota and Minnesota. A typical weed control program in Michigan prior to
2000, included the use of a PRE herbicide such as pyrazon at 3.36 kglha plus
ethofumesate at 1.68 kglha fb two POST standard split herbicide treatments and three to
four cultivations because the herbicides were applied in a band. Michigan sugarbeet
growers applied PRE herbicides on 75% of the sugarbeet ha in 2001 and 60% in 2002
(Renner 20022). A contributing factor to the reduction in PRE herbicide use has been
the registration of the micro-rate in 2000. While no survey was conducted in 2000, it is
estimated that PRE herbicides were applied to more than 90% of the sugarbeet ha in
Michigan. In 2002, the micro-rate and PRE herbicides were applied to 60% of the
sugarbeet ha in Michigan indicating that some of the sugarbeet growers using the micro-
rate POST were also using a PRE herbicide. The reduced cost of the micro-rate
enables sugarbeet growers to broadcast apply the micro-rate compared to the standard-
split that had to be applied in a band; however, the micro-rate requires several timely
applications. Although both the micro-rate and standard-split can be applied in a band,
cultivation is required in either case.

The micro-rate provided sugarbeet growers with a new weed control program
that has several advantages over the previous weed control program. The micro-rate is
typically applied three- to- five times to very small weeds (1.5 cm or less) and provides
good to excellent annual weed control and allows the grower to apply POST herbicides
throughout the day and not just in the evening, which can be a limiting factor with
standard rates. Broadcast applications limit the number of cultivations required for weed
control.

The objectives of these studies were to evaluate weed control and sugarbeet

yield following PRE and POST herbicide applications. We wanted to determine if PRE

 

2 Renner, K. A. Annual sugarbeet grower survey 2002.

41

herbicides increased weed control when followed by (fb) POST herbicides applied as the
micro-rate or standard-split, and if the PRE herbicide applied influenced POST weed
control from the micro-rate or standard-split. Furthermore, we investigated if herbicides
applied at the micro-rate were more injurious to sugarbeets than herbicides applied at
the standard-split. Research trials in sugarbeet growers’ fields were conducted to
compare the results observed in small-plot trials with those in larger scale strip trials.
Sugarbeet growers using the micro-rate were very interested in knowing if a PRE
herbicide improved weed control or affected sucrose yield. The cost of PRE herbicides
In a 25-cm band ranges from $27 to $107/ha and this cost could be eliminated if micro-

rate applications or standard-split applications alone controlled the weeds.

42

MATERIALS AND METHODS
Small plot field research. Experiments were conducted at three sites in Michigan in
2001 and two sites in 2002 in cooperation with Michigan and Monitor Sugar Companies
(Table 1). Hilleshog E-17 was planted at all sites each year. Research at Michigan
State University was conducted at the Saginaw Valley Bean and Beet Research Farm in
Saginaw County. The Michigan Sugar Company sites were located in a grower's fields
in Saginaw County, and The Monitor Sugar Company site was located in Bay County.
The dominant weeds at each site were redroot pigweed (Amaranthus retroflexus L.) and
powell amaranth (Amaranthus powellii S. Wats.), and common lambsquarters
(Chenopodium album L.). In 2001 and 2002, sugarbeet were planted in 71- or 76-cm
wide rows between the dates of April 23 and May 5 (Table 2). Plots were 9.1-m long
and four-rows wide. Herbicide treatments were applied using a tractor mounted
compressed air sprayer in water at 187 L ha‘1 at 207 kPa using XR 8003 spray tips.
Herbicide(s), rate, application timing, number of applications, and herbicide programs
used in small plot research trials in 2001 and 2002 are given in Table 3.

For simplicity, the “8” symbol will designate a pre-mix formulation of herbicide
and “plus” will signify a tank mix of two or more products. From this point forward,
desmedipham 8 phenmedipham at 0.09 kglha plus triflusulfuron at 0.004 kglha plus
clopyralid at 0.023 kglha plus methylated seed oil (M803) at 1.5% will be referred to as
the Betamix micro-rate, and desmedipham & phenmedipham & ethofumesate at 0.09
kglha plus triflusulfuron at 0.004 kglha plus clopyralid at 0.023 kglha plus MSO at 1.5%
will be referred to as the Progress micro-rate. Desmedipham & phenmedipham at 0.56
kglha plus triflusulfuron at 0.017 kglha plus Clopyralid at 0.1 kglha will be referred to as

the Betamix standard-split, and desmedipham & phenmedipham & ethofumesate at 0.28

 

3 Loveland industries Inc., PO Box 1289, Greeley, CO 80632.

43

kglha plus triflusulfuron at 0.017 kglha plus Clopyralid at 0.1 kglha will be referred to as
the Progress standard-split.

Cycloate was applied and incorporated prior to planting (PPI), and ethofumesate,
pyrazon, and s-metolachlor were applied immediately after planting (PRE) at all
locations. When the first emerging weeds reached the cotyledon growth stage the
micro-rate was applied, and the treatment repeated every 5 to 10 d when newly
emerging weeds reached the cotyledon growth stage. The standard-split applications
were applied when the second and fourth micro-rate treatments were applied. The
micro-rate was applied four times and the standard-split was applied twice. The PRE
only treatments were hand weeded so that the effect of herbicide treatment only on
sucrose yield could be determined. Sugarbeet injury and weed control were estimated
visually 14 days after the fourth micro-rate and second standard-split applications using
the rating scale of 0 (no injury) to 100 (completely killed). After the 14 DAT rating, all
treatments were hand weeded throughout the season. Sugarbeets were topped with a
four-row topper, and harvested in October at all sites in 2001 and 2002. The center two-
rows were harvested, weighed, and a sample from each plot was analyzed for
recoverable sucrose by the method outlined by the Association of Official Agriculture
Chemists (1955) by Michigan Sugar Company, Carrollton, MI.

The experimental design was a RCB arranged in a 5 X 5 factorial with four
replicates at each location. Locations were considered as separate environments.
Environments were random, and herbicides were considered fixed effects. Data were
subjected to ANOVA using the PROC MIXED procedure in SAS and means were
compared using Fishers protected LSD test at the 0.05 probability level. Homogeneity of
variance was tested by comparing error mean squares. The error mean squares were
Obtained from the ANOVA table from the individual environmental analyses. By dividing

the smaller error mean square value into the larger error mean square value, a ratio was

44

obtained. If this ratio was less than 5, environments were considered homogeneous,
and the data were combined (personal communication, Alexandra Kravchenko).

Strip trials In production fields. Large strip trials were conducted in three grower
fields in 2001 and four fields in 2002 within the sugarbeet production area in Michigan.
These fields were chosen because the growers applied only POST herbicides at the
micro-rate, and were interested if PRE herbicides reduced sugarbeet populations,
injured sugarbeets or improved weed control compared to the micro-rate alone. Farm
plots were located at Dave Tromble Farms in 2001 and 2002, LaRaCha Farms in 2001
and 2002, Maxwell Farms in 2001, Wackerle Farms in 2002, and Helmrich Farms in
2002. All farm locations were in Bay and Saginaw Counties. Pyrazon at 4.48 kglha,
ethofumesate at 1.68 kglha, and pyrazon plus ethofumesate at 3.36 and 1.68 kglha,
respectively, were applied PRE in each growers field. These were the only PRE
herbicides registered in sugarbeet in 2001 and 2002, and are common PRE herbicides
applied by sugarbeet growers in Michigan. Strips were 4, 6, or 8 rows wide and were 30
to 240 m long depending on equipment and field size. The growers applied their micro-
rate treatments over their fields, including the areas of PRE herbicides. Sugarbeet
populations were counted when sugarbeets had four to six leaves. Sugarbeet injury and
weed control were also evaluated every 7 to 14 d at each production field throughout the
growing season.

Experiments were arranged in a RCBD with three replicates at each location.
Locations were considered as separate environments. Environments were random, and
herbicides were considered fixed effects. Data were subjected to ANOVA using the
PROC MIXED procedure in SAS, and means were compared using Fishers protected
LSD test at the 0.05 probability level. Homogeneity of variance was tested by comparing
error mean squares. The error mean squares were obtained from the ANOVA table

from the individual environmental analyses. By dividing the smaller error mean square

45

value into the larger error mean square value, a ratio was obtained. If this ratio was less
than 5, environments were considered homogeneous, and the data were combined
(personal communication, Alexandra Kravchenko). Each large plot was harvested and
weighed when the rest of the field was harvested with a commercial sugarbeet lifter.
Samples from each plot were analyzed for recoverable sucrose by the method outlined
by the Association of Official Agriculture Chemists (1955) by Michigan Sugar Company,

Carollton, MI.

46

 

RESULTS AND DISCUSSION
Small plot field research. Sugarbeet injury was 5% or less from all POST treatments
in 2001 (Table 4). There were no significant differences in sugarbeet injury from
Betamix and Progress, applied in the micro-rate or standard-split. Sugarbeet
populations were similar, ranging from 141 to 147 plants/30 m in 2001 (Table 4).
Amaranthus spp. control was 83% with the Betamix standard-split and 92% with the
Progress standard-split. The micro-rate provided 86 and 89% Amaranthus spp. control
with Progress and Betamix, respectively. Common lambsquarters control was 91 % with
the Betamix micro-rate and 95% with the Betamix standard-split in 2001 (Table 4). All
POST treatments provided similar weed control, but no treatments provided 100%
control. Sucrose yields were similar among all POST treatments.

When PRE herbicides were applied prior to POST herbicides, there were no
significant differences in sugarbeet injury and populations between POST treatments in
2001 (Table 5). Amaranthus spp. control was greater with the Betamix micro-rate than
the Progress micro-rate, but was similar to the standard-split application of Betamix or
Progress and to the PRE only/hand-weeded treatments. Common lambsquarters
control was 97% with all POST herbicide treatments combined over PRE treatments
(Table 5). Sucrose yields were similar among all POST treatments combined over PRE
treatments. In 2001, PRE herbicides increased common lambsquarters control and
some PRE herbicides increased Amaranthus spp. control, but applying PRE herbicides
did not increase sucrose yield compared to sugarbeets treated with only POST
herbicides (Tables 4 and 5).

Cycloate reduced sugarbeet populations in 2001 with and without POST
herbicides (Tables 6 and 7), but this did not result in a significant reduction in sucrose.
This was similar to the results observed by Wilson et al. (1990), who reported a

reduction in sugarbeet populations by cycloate. PRE herbicides fb POST herbicides,

47

resulted in 6% or less sugarbeet injury in 2001 (Table 7). All PRE herbicide applications
increased weed control in PRE/POST combinations compared to no PRE, but there was
no significant difference in sucrose yield. Therefore, in 2001 weed control was greater
with PRE/POST combinations but there were no significant differences in sucrose yield.
All PRE herbicide applications provided similar control of Amaranthus spp. and common
lambsquarters.

In 2002, sugarbeet injury from the Betamix standard-split application was 29%
compared to 38% from the Betamix micro-rate and 43% from the Progress micro-rate
and standard-split (Table 8). Sugarbeet populations were not significantly influenced by
POST herbicides, ranging from 172 to 193 plants/30 m in 2002 (Table 8). Amaranthus
spp. control was 96% with the Betamix standard-split and 100% with the Progress micro-
rate; however, differences were not significant. Common lambsquarters control was
90% from the Betamix micro-rate and 100% from the Progress standard-split in 2002
(Table 8). Although there were some differences In weed control among POST
herbicide treatments, sucrose yields were similar among all POST herbicide treatments.

In 2002, sugarbeet injury increased significantly where PRE herbicides were fb
the Progress micro-rate and standard-split, and the Betamix standard-split compared to
the Betamix micro-rate (Table 9). PRE herbicides caused 28% sugarbeet injury, and the
Progress micro-rate when combined over PRE herbicide applications resulted in 44%
sugarbeet injury. However, sugarbeet populations were not significantly reduced by
these treatments. Amaranthus spp. control was excellent with all POST herbicide
treatments combined over PRE herbicide treatments (Table 9). Common lambsquarters
control was 92 to 97% in all POST herbicide treatments combined over PRE herbicides.
The Progress micro-rate provided significantly greater Amaranthus spp. control than the

Betamix micro-rate and standard-split (Table 9). Although there were some differences

48

in weed control among POST herbicide treatments, sucrose yields were similar among
all POST herbicide treatments combined over PRE herbicide treatments.

S-metolachlor reduced sugarbeet populations compared to ethofumesate in 2002
with and without POST herbicides (Tables 10 and 11), and sucrose yields were reduced
significantly compared to cycloate, ethofumesate, and no PRE herbicide. However, we
would expect the no PRE herbicide treatment to have the highest stand. Amaranthus
spp., common lambsquarters control, and sucrose yields were similar among all PRE
herbicide treatments including the no PRE treatment. Therefore, in 2002 weed control
was similar with PRE/POST herbicide combinations and there were no significant
differences in sucrose yield.

These data show that PRE herbicides can increase Amaranthus spp. and
common lambsquarters control depending on environmental conditions. These data
also show that sugarbeet injury increases when rainfall is greater than normal and
temperatures are lower than normal as experienced in 2002 (Table 2). Under cool wet
conditions, sugarbeets are more susceptible to herbicide injury compared to the warm
and dry conditions experienced in 2001; however, under these dry conditions many PRE
herbicides are ineffective. Smith and Schweizer (1987) reported that favorable spring
temperatures and soil moisture conditions favored plant uptake of herbicides. Weed
control was often increased by PRE herbicides, but sucrose yields were not. Morishita
and Downard (1995) reported greater common lambsquarters control from ethofumesate
compared to the no PRE herbicide treatment when fb desmedipham plus
phenmedipham plus ethofumesate. However, Dexter et al. (1988) reported increased
sugarbeet injury and weed control when POST herbicide treatments were applied over
PPI herbicides, but not PRE herbicides. They hypothesized that the inadequate rainfall
in 1988 contributed to the poor control from Antor PRE. Renner and Powell (1991)

reported inconsistent weed control with PRE herbicides and attributed it to inadequate

49

rainfall in 1998. While our PRE herbicides were applied broadcast, sugarbeet growers
would apply these herbicides in a band and cultivate to reduce expenses. We also
found that there were little differences between the micro-rate and the stand-split with
Betamix or with Progress. POST herbicide applications in sugarbeet need to be applied
timely to achieve satisfactory control. Particularly the first POST application may be
more important than the choice of herbicide or the number of applications. Herbicides
must be applied to weeds with less than two- true leaves and should be applied when
the weeds are in the cotyledon growth stage. These data indicated some advantage
with Progress compared to Betamix which was not expected based on previous
observations.

Strip trials In production fields. Based on the comparisons of error mean squares,
Dave Tromble Farms in 2001, LaRaCha Farms in 2001 and 2002, Wackerle Farms in
2002, and Helmrich Farms in 2002 were combined: and sugarbeet injury and
recoverable sucrose are reported in Table 12. Maxwell Farms in 2001 is reported in
Table 13 and Dave Tromble Farms in 2002 is reported in Table 14. When combined
over five locations in 2001 and 2002, PRE herbicides did not affect sugarbeet
populations or recoverable sucrose per ha (Table 12). Also at Maxwell Farms in 2001
(Table 13) and at Dave Tromble Farms in 2002 (Table 14) PRE herbicides did not
significantly affect sugarbeet populations or recoverable sucrose per ha. Sucrose yields
increased in plots treated with PRE herbicides at Maxwell Farms in 2001, but only 30 m
of each plot at this location was harvested because half of some plots were destroyed by
cultivation. At all other locations, at least 150 m of each plot was harvested. This may
have contributed to the larger differences in sucrose yield among treatments. Weed
control was excellent in all treatments at all locations except at the Maxwell Farm in
2001 and the Wackerle Farm in 2002, weed control was poor in general and there was

no observable effect of the PRE herbicides (data not presented).

50

Sugarbeet growers were disappointed with the efficacy of the PRE herbicides
under these conditions, and felt there was no benefit from the PRE herbicides (personal
communication). At Maxwell Farms in 2001 and Wackerle Farms in 2002, excessive
early season moisture prevented the timely application of POST herbicides, and a poor
sugarbeet population contributed to the poor weed control. These data suggest that
PRE herbicides were not required in production fields as weed control and sucrose
yields were not significantly increased. These results are somewhat different than the
small plot research, where there was some advantage to PRE herbicides with respect to
Amaranthus spp. anc common lambsquarters control; however, sucrose yields were
similar with or without PRE herbicides at all locations.

We observed a reduction in sugarbeet population from cycloate in 2001 and s-
metolachlor in 2002. Schweizer (1979) reported a reduction in sugarbeet population and
top growth from cycloate and ethofumesate. Wilson et al. (1990) also reported a
decrease in sugarbeet population and size from cycloate and ethofumesate; however, by
the end of the growing season sugarbeets had recovered from early season injury and
none of the herbicides reduced root yield. Sugarbeet growers must decide if the risk of
stand loss under cool, wet conditions is outweighed by the benefit of six to eight weeks
of weed control. Starke and Renner (1996) reported that sugarbeet response to POST
herbicides was not affected by PPI or PRE herbicides. We observed similar results in
2001 but not in 2002. Rainfall in 2002 may have increased sugarbeet uptake of PRE
herbicides and cool, wet conditions slow metabolism of herbicide in sugarbeet.
Therefore growers must decide if there is a greater risk applying POST herbicides

following PRE herbicides under cool, wet conditions.

51

LITERATURE CITED

Association Of Official Agriculture Chemists. 1955. Official methods of analysis. 8th ed.
Washington, DC. pp. 564-568.

Dexter, A. G. 1994. History of sugarbeet (Beta vulgaris) herbicide rate reduction in North
Dakota and Minnesota. Weed Technol. 8:334-337.

Dexter A. G. and J. L. Luecke. 1998. Special survey on micro-rate, 1998. Sugarbeet
Res. Ext. Rep. 29:64-75.

Dexter A. G. and J. L. Luecke. 1988. Soil applied and postemergence herbicides at six
locations. Sugarbeet Res. Ext. Rep. 19:45-48.

Dexter, A. G., J. L. Luecke, and M. Law. 1988. Soil applied and postemergence
herbicides at six locations. Sugarbeet Res. Ext. Rep. 19:45-48

Morishita, D. W., and R. W. Downard. 1995. Weed control in sugar beets with
triflusulfuron as influenced by herbicide combination, timing, and rate. J. Sugar
Beet Res. 32:23-34.

Renner, K. A., and G. E. Powell. 1991. Velvetleaf (Abutilon theophrastr) control in
sugarbeet (Beta vulgaris). Weed Technol. 5:97-102.

Smith G. A. E. E. Schweizer, and S. S. Martin. 1982. Differential response of sugarbeet
populations to herbicides. Crop Sci. 22:81-85.

Starke, R. J. and K. A. Renner. 1996. Velvetleaf (Abutilon theophrastr) and sugarbeet
(Beta vulgaris) response to triflusulfuron and desmedipham plus phenmedipham.
Weed Technol. 121-126.

Schweizer, E. E. 1979. Weed control in sugarbeets (Beta vulgaris) with mixtures of
cycloate and ethofumesate. Weed Sci. 27:516-519.

Schweizer E. E. and A. G. Dexter 1987. Weed control in sugarbeets (Beta vulgaris) in
North America. Rev. Weed Sci. 1987. 3:113-133

Wilson, R. G., J. A. Smith, and C. D. Yonts. 1990. Effect of seeding depth, herbicide,

and variety on sugarbeet (Beta vulgaris) emergence, vigor, and yield. Weed
Technol. 4:739-742.

52

 

Table 1. Soil series, type, organic matter, and planting dates for small plot research

trials at each location in 2001 and 2002.

 

 

 

 

 

 

Site Soil Planting
Location Year Series Type OM“ Variety Date Row
Width

(°/°) (cm)

Michigan 2001 Zilwaukee Silty Clay 3.3 HM E-17 4/27 71

State

Univ.

Michigan 2001 Sloan- Clay 9.7 HM E-17 5/3 76

Sugar Co. Ceresco

Monitor 2001 Londo Clay 2.3 HM E-17 4/26 76 5

Sugar Co. Loam

Michigan 2002 Zilwaukee Silty Clay 3.6 HM E-17 5/5 71

State

Univ.

Michigan 2002 Sloan- Clay 10.2 HM E-17 4/23 76

Sugar Co. Ceresco

 

“Abbreviations: 0M, organic matter.

53

Table 2. Deviations from the normal monthly precipitation and mean temperature in
2001 and 2002 at Michigan State University Saginaw Valley Beet & Bean Research

Farm, Saginaw, MI.

 

 

 

Precipitation Temperature
(cm) (C)
Month 2001 2002 2001 2002
April -1.0 1.3 0.8 -0.4
May 0.5 3.8 -1.4 -3.3
June -2.6 . -O.6 -0.1 -0.1
July -2.3 0.4 -0.2 0.7
August -3.4 1 .4 1 .4 -0.7
September 2.9 -6.0 -1 .4 1.2

 

Table 3. Herbicide, rate, application timing, number of applications, and herbicide

programs used in small plot research trials in 2001 and 2002.

 

 

Herbicide(s)“ Rate Application Number of Herbicide
timinga Applications program

kglha
Desm. plus phen. plus 0.045, 0.045, POST 4 Betamixb
tfsu. plus clpy. plus 0.004, and 0.023 micro-rate
MSO
Desm. plus phen plus 0.03, 0.03, 0.03, POST 4 Progressb
etho. plus tfsu. plus 0.004, and 0.023 micro-rate
clpy. plus MSO
Desm. plus phen. plus 0.28, 0.28, 0.017, POST 2 Betamix
tfsu. plus clpy.° and 0.1 standard-split
Desm. plus phen plus 0.09, 0.09, 0.09, POST 2 Progress
etho. plus tfsu. plus 0.017, and 0.1 standard-split
clpy.°
S-metolachlor 1 .42 PRE 1 Preemergence
Pyrazon 4.48 PRE 1 Preemergence
Ethofumesate 1 .68 PRE 1 Preemergence
Cycloate 3.36 PPI 1 Preemergence

 

aAbbreviations: desm., desmedipham; phen., phenmedipham; etho., ethofumesate;
tfsu., triflusulfuron; clpy., Clopyralid; MSO, methylated seed oil.
bMSO was used at 1.5 % v/v.
°Clopyralid was only applied in the second split of the standard-split application.

55

Table 4. Sugarbeet injury and population, Amaranthus species and common

lambsquarters control, and recoverable sucrose per hectare from POST herbicides only

combined at three locations in 2001‘“.

 

 

POST Herbicide Sugarbeet Sugarbeet
treatment rate injury population AMASS CHEAL RWSH
kglha —- % - Plants/30 m — % control — kglha
No POST plus - 0a 142a 100a 100a 6,726a
handweeded
Desm. plus 0.045, 5b 143a 89b 91c 6,590a
phen. plus tfsu. 0.045,
plus clpy. plus 0.004,
M80“ and 0.023
Desm. plus 0.03, 3ab 147a 86b 930 6,079a
phen. plus etho. 0.03,
plus tfsu. plus 0.03,
clpy. plus MSO d 0.004,
and 0.023

Desm. plus 0.28, 5b 141a 83b 95bc 6,646a
phen. plus tfsu. 0.28,
plus clpy.° 0.017,

and 0.1
Desm. plus 0.09, 4b 136a 92ab 94c 6,333a
phen. plus etho. 0.09,
plus tfsu. plus 0.09,
clpy.° 0.017,

and 0.1

 

aMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.
bAbbreviations: desm., desmedipham; phen., phenmedipham; etho., ethofumesate;
tfsu., triflusulfuron; clpy., clopyralid; MSO, methylated seed oil; AMASS (Amaranthus
species), redroot pigweed and powell amaranth; CHEAL, common lambsquarters;
RWSH, recoverable white sucrose per hectare.
cSugarbeet populations were measured at harvest, and AMASS and CHEAL control
were rated 14 days after the last POST application.

dMSO was used at 1.5 % v/v and treatments containing MSO were applied four times
and treatments not containing MSO were applied twice.
°Clopyralid was only applied in the second split of the standard-split application.

56

Table 5. Sugarbeet injury and population, Amaranthus species and common

lambsquarters control, and recoverable sucrose per hectare from POST herbicides

combined over PRE herbicides at three locations in 2001“.

 

 

 

POST Herbicide Sugarbeet Sugarbeet
treatment rate injury population AMASS CHEAL RWSH
kglha -- %— Plants/30 m % control — kglha
PRE only plus - 43 140a 1003 1003 6,4643
handweeded
Desm. plus 0.045, 63 1413 963b 97a 6,6393
phen. plus tfsu. 0.045,
plus clpy. plus 0.004,
MSO ° and 0.023
Desm. plus 0.03, 63 1403 93C 973 6,3753
phen. plus etho. 0.03,
plus tfsu. plus 0.03,
clpy. plus MSO ° 0.004,
and 0.023

Desm. plus 0.28, 43 1423 94bc 973 6.7583
phen. plus tfsu. 0.28,
plus clpy.f 0.017,

and 0.1
Desm. plus 0.09, 53 1413 963b 97a 6,4393
phen. plus etho. 0.09,
plus tfsu. plus 0.09,
clpy.‘ 0.017,

and 0.1

 

aMeans within a column followed by the same letter are not different, according to

Fisher’s protected LSD at P 0.05.

bPOST treatments are combined over all PRE treatments including No PRE, pyrazon at

4.48, s-metolachlor at 1.42, ethofumesate at 1.68, and cycloate at 3.36 kg ailha.

°Abbrevi3tionsz desm., desmedipham; phen., phenmedipham; etho., ethofumesate;
tfsu., triflusulfuron; clpy., clopyralid; MSO, methylated seed oil; AMASS (Amaranthus
species), redroot pigweed and powell amaranth; CHEAL, common lambsquarters;

RWSH, recoverable sucrose per hectare.

dSugarbeet populations were measured at harvest, and AMASS and CHEAL control
were rated 14 days after the last POST application.
°MSO was used at 1.5 % v/v and treatments containing MSO were applied four times

and treatments not containing MSO were applied twice.
fClopyralid was only applied in the second split of the standard-split application.

Table 6. Sugarbeet injury and population, Amaranthus species and common
lambsquarters control, and recoverable sucrose per hectare from PRE herbicides at

three locations in 2001“.

 

 

 

PRE Herbicide Sugarbeet
treatment rate population AMASS CHEAL RWSH
kglha Plants/30 m % control — kglha

No PRE plus - 1483 100 100 6,5033
ha ndweeded

S-metolachlor 1 .42 1473 100 100 6,5033
Ethofumesate 1.68 1493 100 100 6,7803
Pyrazon 4.48 1483 100 100 6,5853
Cycloate 3.36 139b 100 100 6,3953

 

aMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

bAll treatments were hand weeded.

cAbbreviations: AMASS (Amaranthus species), redroot pigweed and powell amaranth;
CHEAL, common lambsquarters; RWSH, recoverable sucrose per hectare.
dSugarbeet populations were measured at harvest, and AMASS and CH EAL control
were rated 14 days after the last POST application.

58

Table 7. Sugarbeet injury and population, Amaranthus species and common
lambsquarters control, and recoverable sucrose per hectare from PRE herbicides

combined over POST herbicides at three locations in 2001“.

 

 

PRE Herbicide Sugarbeet Sugarbeet
treatment rate injury population AMASS CHEAL RWSH
kglha — % — Plants/30 m — % control— kglha
No PRE - 43 1413 90b 95b 6,4613
S-metolachlor 1 .42 63 1413 963 983 6,4933
Ethofumesate 1 .68 53 1433 983 99a 6,7903
Pyrazon 4.48 43 1423 973 99a 6,5433
Cycloate 3.36 63 1 34b 96a 98a 6,3903

 

aMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

bAbbreviations: AMASS (Amaranthus species), redroot pigweed and powell amaranth;
CHEAL, common lambsquarters; RWSH, recoverable white sucrose per hectare.

°PRE treatments are combined over all POST treatments including desmedipham plus
phenmedipham (1 :1 ratio) at 0.09 kglha plus triflusulfuron at 0.004 kglha plus clopyralid
at 0.023 kglha, plus MSO at 1.5% v/v applied four times; desmedipham plus
phenmedipham plus ethofumesate (1 :1 :1 ratio) at 0.09 kglha plus triflusulfuron at 0.004
kglha plus clopyralid at 0.023 kglha, plus MSO at 1.5% v/v applied four times;
desmedipham plus phenmedipham at 0.56 kglha plus triflusulfuron at 0.017 kglha plus
clopyralid at 0.1 kglha applied two times; and desmedipham plus phenmedipham plus
ethofumesate at 0.56 kg/ha plus triflusulfuron at 0.017 kglha plus clopyralid at 0.1
applied two times.

dSugarbeet populations were measured at harvest, and AMASS and CHEAL control
were rated 14 days after the last POST application.

59

Table 8. Sugarbeet injury and population, Amaranthus species and common

lambsquarters control, and recoverable sucrose per hectare from POST herbicides only

 

 

 

at two locations in 2002“”.
POST Herbicide Sugarbeet Sugarbeet
treatment rate injury population AMASS CHEAL RWSH

kglha — %— Plants/30 m % control — kglha
No POST plus - 03 1773 1003 1003 6,7233
handweded
Desm. plus 0.045, 38bc 1723 993 90c 7,0843
phen. plus 0.045,
tfsu. plus clpy. 0.004,
plus MSO “ and

0.023
Desm. plus 0.03, 43c 1 88a 1 003 98ab 7,0273
phen plus 0.03,
etho. plus tfsu. 0.03,
plus clpy. plus 0.004,
MSO d and

0.023
Desm. plus 0.28, 29b 1933 963 93bc 7,2203
phen. plus 0.28
tfsu. plus clpy.° 0.017,

and 0.1
Desm. plus 0.09, 43c 1913 983 1003 6,8833
phen plus 0.09,
etho. plus tfsu. 0.09,
plus clpy.° 0.017,
and 0.1

 

a‘Means within 3 column followed by the same letter are not different, according to

Fisher’s protected LSD at P 0.05.
bAbbreviations: desm., desmedipham; phen., phenmedipham; etho., ethofumesate;
MSO, methylated seed oil; AMASS (Amaranthus species), redroot pigweed and powell
amaranth; CHEAL, common lambsquarters; RWSH, recoverable white sucrose per

hectare.

°Sugarbeet populations were measured at harvest, and AMASS and CHEAL control

were rated 14 days after the last POST application.

dMSO was used at 1.5 % v/v and treatments containing MSO were applied four times

and treatments not containing MSO were applied twice.
°Clopyralid was only applied in the second split of the standard-split application.

60

Table 9. Sugarbeet injury and population, Amaranthus species and common

lambsquarters control, and recoverable sucrose per hectare from POST herbicides

combined over PRE herbicides at two locations in 2002"”.

 

 

 

POST Herbicide Sugarbeet Sugarbeet

treatment rate injury population AMASS CHEAL RWSH
kglha — %— Plants/30 m % control — kglha

PRE only plus - 283 1813 1003 1003 6,7063

handweeded

Desm. plus 0.045, 343b 1873 993 94c 7,1703

phen. plus 0.045,

tfsu. plus clpy. 0.004, and

plus MSO d 0.023

Desm. plus 0.03, 0.03, 44C 1873 1003 973b 6,8123

phen plus 0.03,

etho. plus tfsu. 0.004, and

plus clpy. plus 0.023

M50d

Desm. plus 0.28, 0.28, 39bc 1783 983 92C 7,0343

phen. plus 0.017, and

tfsu. plus 0.1

clpy.°

Desm. plus 0.09, 0.09, 37b 1893 973 96abc 6,8663

phen plus 0.09,

etho. plus tfsu. 0.017, and

plus clpy.° 0.1

 

a'Means within a column followed by the same letter are not different, according to
Fisher's protected LSD at P 0.05.

bPOST treatments are combined over all PRE treatments including pyrazon at 4.48, s-
metolachlor at 1.42, ethofumesate at 1.68, and cycloate at 3.36 kg ailha.
°Abbreviations: desm., desmedipham; phen., phenmedipham; etho., ethofumesate;
tfsu., triflusulfuron; clpy., Clopyralid; MSO, methylated seed oil; AMASS (Amaranthus
species), redroot pigweed and powell amaranth; CHEAL, common lambsquarters;
RWSH, recoverable white sucrose per hectare.

cSugarbeet populations were measured at harvest, and AMASS and CHEAL control
were rated 14 days after the last POST application.

dMSO was used at 1.5 % v/v and treatments containing MSO were applied four times
and treatments not containing MSO were applied twice.

°Clopyralid was applied in the second split of the standard-split application.

61

Table 10. Sugarbeet injury and population, Amaranthus species and common
lambsquarters control, and recoverable sucrose per hectare from POST herbicides at

two locations in 2002“.

 

 

 

 

PRE Herbicide Sugarbeet
treatment rate population AMASS CHEAL RWSH
kglha Plants/30 m % control — kglha .
No PRE - 177bc 100 100 6,7993b
S-metolachlor 1.42 163C 100 100 5,777C
Ethofumesate 1.68 1913b 100 100 6,721ab
Pyrazon 4.48 179bc 100 100 6,563bc I
Cycloate 3.36 186bc 100 100 7,6713

 

“Means within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

bAll treatments were hand weeded.

cAbbreviations: AMASS (Amaranthus species), redroot pigweed and powell amaranth;
CHEAL, common lambsquarters; RWSH, recoverable white sucrose per hectare.
dSugarbeet populations were measured at harvest, and AMASS and CHEAL control
were rated 14 days after the last POST application.

62

Table 11. Sugarbeet injury and population, Amaranthus species and common
lambsquarters control, and recoverable sucrose per hectare from PRE herbicides

combined over POST herbicides at two locations in 2002“.

 

 

 

PRE Herbicide Sugarbeet Sugarbeet
treatment rate injury population AMASS CHEAL RWSH
kglha — % — Plants/30 m % control — kglha
No PRE - 37a 1843b 983 963 6.9773
S-metolachlor 1.42 403 178D 993 953 6,7753
Ethofumesate 1.68 37a 1893 993 97a 6,9113
Pyrazon 4.48 383 1843b 983 953 6,7333
Cycloate 3.36 363 1873b 993 963 7.1903

 

aMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

bAbbreviations: AMASS (Amaranthus species), redroot pigweed and powell amaranth;
CHEAL, common lambsquarters; RWSH, recoverable white sucrose per hectare.

°PRE treatments are combined over all POST treatments including desmedipham plus
phenmedipham (1 :1 ratio) at 0.09 kglha plus triflusulfuron at 0.004 kglha plus clopyralid
at 0.023 kglha, plus MSO at 1.5% applied four times; desmedipham plus phenmedipham
plus ethofumesate (1 :1 :1 ratio) at 0.09 kglha plus triflusulfuron at 0.004 kglha plus
clopyralid at 0.023 kg/ha, plus MSO at 1.5% v/v applied four times; desmedipham &
phenmedipham at 0.56 kglha plus triflusulfuron at 0.017 kglha plus clopyralid at 0.1
kglha applied two times; and desmedipham 8. phenmedipham 8 ethofumesate at 0.56
kglha plus triflusulfuron at 0.017 kglha plus Clopyralid at 0.1 applied two times.
dSugarbeet populations were measured at harvest, and AMASS and CHEAL control
were rated 14 days after the last POST application.

63

Table 12. Sugarbeet stand and recoverable white sucrose per hectare combined over
Tromble Farms 2001, LaRaCha Farms 2001 and 2002, Wackerle Farms 2002, and

Helmrich Farms 2002“.

 

 

Preemergence Herbicide Sugarbeet

treatments rate population RWSH
kglha plants/30 m kglha

No PRE - 141a 5,7893

Pyrazon 4.48 1393 5,9623

Pyrazon plus 3.36 plus 1383 5,8273

ethofumesate 1 .68

 

aMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

bPOST micro-rate herbicide treatments were applied three to five times at each location
by the sugarbeet grower.

°Abbreviationsz RWSH, recoverable white sucrose per hectare.

dSugarbeet populations were measured at harvest.

64

 

Table 13. Sugarbeet stand and recoverable white sucrose per hectare at Maxwell

Farms In 2001“.

 

 

Preemergence Herbicide Sugarbeet

treatments rate population RWSH
kglha plants/30 m kglha

No PRE - 843 8,6273

Pyrazon 4.48 1033 9,5083

Pyrazon plus 3.36 plus 853 9,9783

ethofumesate 1 .68

 

a'Means within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

bPOST micro-rate herbicide treatments were applied three to five times at each location
by the sugarbeet grower.

°Abbreviationsz RWSH, recoverable white sucrose per hectare.

clSugarbeet populations were measured at harvest.

65

 

Table 14. Sugarbeet stand and recoverable white sucrose per hectare at Dave Tromble

Farms in 2002“.

 

 

Preemergence Herbicide Sugarbeet

treatments rate population RWSH
kglha plants/30 m kglha

No PRE - 1463 5,4933

Pyrazon 4.48 1223 5,8893

Pyrazon plus 3.36 plus 1233 5,8393

ethofumesate 1 .68

 

aMeans within a column followed by the same letter are not different, according to
Fisher’s protected LSD at P 0.05.

t’POST micro-rate herbicide treatments were applied three to five times at each location
by the sugarbeet grower. ’

°Abbreviationsz RWSH, recoverable white sucrose per hectare.

dSugarbeet populations were measured at harvest.

66

 

CHAPTER 4
RESPONSE OF SUGARBEET (Beta vulgaris) VARIETIES AND LINES TO
POSTEMERGENCE HERBICIDE TREATMENTS.

Abstract. Previous research has shown a differential response of sugarbeet varieties to
herbicides. Injury may reduce sugarbeet leaf area, yield, or sucrose content. This
research evaluated the response of fourteen sugarbeet varieties and four USDA
sugarbeet lines to postemergence (POST) herbicides applied three times at reduced
rates, termed the “micro-rate”. A tank mixture of desmedipham plus phenmedipham (1 :1
ratio) at 0.09 kg ai/ha plus triflusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg
aelha plus methylated seed oil (MSO) at 1.5% v/v was applied three times at weekly
intervals beginning at the cotyledon growth stage. These experiments were conducted
in the growth chamber and in the field. Leaf area, fresh weights, and dry weights were
recorded 1 wk after the third micro-rate applciation and compared to the respective
control. Sugarbeet varieties differed in their response to micro-rate treatments. Micro-
rate treatments reduced leaf area of the fourteen sugarbeet varieties by 3 to 35% and
dry weights by 11 to 59%. Micro-rate treatments reduced leaf area of the USDA lines by
20 to 29% and dry weights by 47 to 53%. The commercial variety Hilleshog E17 and
USDA line WC 93404 were the most tolerant to micro-rate treatments in both studies
with a 3 and 20% reduction in leaf area, and 19 and 47% reduction in dry weight,
respectively. Hilleshog E17, a diploid, did not have a significant reduction in leaf area,
fresh weight, or dry weight in growth chamber of field studies. Beta 5736, a triploid, had
significant reductions in leaf area, fresh weight, and dry weight in both growth chamber
studies and dry weight in the field study. Other varieties and lines varied in response
dependent on experimental conditions. Therefore reductions in sugarbeet leaf area and
biomass will occur following POST herbicide applications, and the degree of response

will be dependent on both variety and environment.

67

 

Nomenclature: desmedipham; phenmedipham; ethofumesate; triflusulfuron;
Clopyralid; common lambsquarters, Chenopodium album L. if1 CHEAL; redroot
pigweed, Amaranthus retroflexus L. # AMARE; pigweed species, Amaranthus
retroflexus and Amaranthus powellii S. Wats. # AMASS; sugarbeet, Beta vulgaris L.
Hillshog E-17 and Beta 5400.

Additional Index words: micro-rate.
Abbreviations: GDD, growing degree days, POST, postemergence.

 

 

' Letters following this symbol are a WSSA-approved computer code from Composite List of
Weeds, Revised 1989. Available only on computer disk from WSSA, 810 East 10th Street,

Lawrence, KS 66044-8897.

68

INTRODUCTION

Sugarbeet (Beta vulgaris L.) growers face many production challenges, and one
of the most critical choices is variety selection. Sugarbeet varieties are chosen based on
their yield potential, cost, disease resistance, herbicide tolerance, and emergence
potential. Without a uniform plant population adapted to the production problems within
the field or region, the grower will have difficulty achieving economical sucrose yields
(Smith et al. 2001). Establishing an optimum sugarbeet population is critical to achieve
the greatest sucrose yields. A uniform sugarbeet population minimizes variability among
individual sugarbeets, and limits the area where weeds may emerge in the row. There
are great differences in variety emergence. Sugarbeet often are overseeded because
sugarbeet seedlings are weak and from 20 to 60% of the seedlings can be lost to
unfavorable soil moisture, soil crusting, wind damage, insects, and seedling diseases
(Schweizer and Dexter 1987). Sugarbeet seed is very expensive relative to other major
agronomic crops so varieties with the greatest field emergence are preferred by
sugarbeet growers.

Sugarbeet varieties differ in their susceptibility to herbicide treatments (Dexter
and Luecke 1997, Wilson 1999, Wilson et al. 1990, and Smith and Schweizer1983).
Dexter and Kern (1978) reported that sugarbeet varieties varied in response to EPTC,
and there was a significant herbicide by variety by year interaction. In 2 of 3 years,
varieties responded differently to EPTC, but in one year there was no herbicide
response to any of the varieties. In other research, herbicides including cycloate applied
pre-plant incorporated (PPI), ethofumesate applied preemergence (PRE), and
desmedipham plus phenmedipham applied POST reduced plant weight of eight
sugarbeet varieties by 39 to 55% 45 days after planting and there were significant
herbicide by variety interactions (Smith and Schweizer 1983). However, by harvest root

yield reductions from herbicide treatments averaged 5% and herbicide by variety

69

interactions were no longer significant. Wilson (1999) reported a significant reduction in
the sugarbeet root yield, percent sucrose, and sucrose yield of nine sugarbeet varieties
when treated with desmedipham plus phenmedipham at 0.36 kglha with either
triflusulfuron at 0.018 kglha or ethofumesate at 0.016 kglha.

Since these studies were conducted, herbicide programs in sugarbeet have

changed significantly. In recent years the use of PRE and PPI applied herbicides have

’53?

declined and the use of POST applied herbicides have increased (Wilson 1999). Data

from eastern North Dakota and Minnesota indicated that on average each ha of

 

sugarbeet received 4.2 POST herbicide applications (Dexter et al. 1997). Combinations 5,. -; '
of desmedipham plus phenmedipham or desmedipham plus phenmedipham plus B;
ethofumesate with triflusulfuron and Clopyralid were applied POST in tank mixtures for

broadleaf weed control and annual grass suppression. The most common POST

program is referred to as the micro-rate (desmedipham plus phenmedipham (1 :1 ratio) at

0.09 kglha plus triflusulfuron at 0.004 kglha plus clopyralid at 0.023 kglha plus MSO at

1.5% v/v). Furthermore, new sugarbeet varieties are released in each growing region of

the US. each year, and susceptibility to POST herbicides is not known. Our objective

was to determine if sugarbeet varieties differed in their susceptibility to POST micro-rate

herbicides. Furthermore, we were interested if variety response to POST herbicides

could be correlated to ploidy level. This information would be useful to sugarbeet

growers in designing POST weed management systems that were not injurious to

sugarbeet. Lastly, if a particular sugarbeet population was highly susceptible or tolerant

to POST herbicides these lines could be exploited in future sugarbeet breeding

research.

70

MATERIALS AND METHODS
Growth chamber research. Commercial sugarbeet varieties and USDA lines were
grown in growth chambers with a photoperiod Of 16:8 h (lightzdark) and thermoperiod of
24:14 C (dayznight). Eight to ten sugarbeet seeds of each variety or line were seeded in
plastic pots (10-Cm square by 15-cm depth) containing a mixture of sphagnum peat and
perlite. Each pot was thinned to four plants per pot three days after emergence. Pots
were watered daily as needed and fertilized once each week with 50 ml of N, P205, K20
(20-20-20) at 20 ppm. The herbicides applied in the micro-rate were desmedipham plus
phenmedipham (1 :1 ratio) at 0.09 kglha plus triflusulfuron at 0.004 kglha plus Clopyralid
at 0.023 kglha plus MSO2 at 1.5% v/v. Herbicides were applied three times on weekly
intervals with a single tip track-sprayer equipped with an 8003E3 spray tip calibrated to
deliver 187 L ha'1 at 207 kPa. Fresh and dry weights and leaf area of three sugarbeet
plants from each pot were recorded one wk after the last treatment. The experimental
design was a CRD with four replications and was repeated. Data were subjected to
ANOVA using the PROC MIXED procedure in SAS and means were separated using
Fishers Protected LSD at (P 0.05).

In the first experiment, two triploids Beta 5736 and Beta 5400 and two diploids
Hilleshog E-17 and ACH 555 were screened for sensitivity to the micro-rate. In the
second experiment, there were four triploids Spartan, Beta 5451, Beta 5172, and Beta
5736, and eight diploids Prompt, Hilleshog E-17, Hilleshog E-33, Hilleshog E-38,
Hilleshog RH-5, ACH 963, ACH 913, and ACH 1353. These varieties were the twelve
sugarbeet varieties in the Michigan State University Sugarbeet Advancement variety
trials in 2002. In addition, two former commercial varieties ACH 185 a triploid, and USH

20 a diploid, and four USDA lines including WC 93404 (sp85576cms X 92HSZ5), WC

 

2 Loveland industries Inc., PO Box 1289, Greeley, co 80632.
3 Teejet even fan tips. Spraying Systems Co., North Ave. and Schmale Road, Wheaton, IL 60188.

71

93406 (sp85657cms X 92H825), WC 93407 (FC607cms X 92H825), and WC 93409
(C40 X 92H326) were included with the 12 commercial varieties.

Field research. Fourteen sugarbeet varieties and four USDA lines were planted with a
small-plot planter on April 30, 2002 (Table 6). Plots were four rows wide by 7.6 m, and
the center 3 m of each plot were treated with herbicide. The first micro-rate treatment
was applied when sugarbeet were at the cotyledon growth stage and was repeated 7
and 14 (I later. The herbicides applied in the micro-rate were desmedipham plus
phenmedipham (1 :1 ratio) at 0.09 kglha plus triflusulfuron at 0.004 kglha plus clopyralid
at 0.023 kglha plus MSO2 at 1.5% v/v. Herbicide treatments were applied with a back-
pack compressed air sprayer equipped with an 8003E spray tip calibrated to deliver 187
L ha" at 207 kPa. The experimental design was a RCBD in a split-plot arrangement with
three replications. The whole-plot was variety and sub-plot was herbicide treatment.
Treatments consisted of either treated or untreated sugarbeet. Three plants from each of
the center two rows of the treated area, and three plants from each of the center two
rows of the untreated area were harvested one wk after the third micro-rate treatment.
Leaf area and leaf fresh weights were measured at harvest and dry weights were

recorded 1 wk later.

72

 

RESULTS AND DISSCUSSION
Growth chamber research. In the first experiment, herbicide treatments reduced leaf
fresh weight, dry weight, and leaf area of Beta 54004 and Beta 5736; however, there was
no significant reduction in the measured variables for the varieties ACH 5555 and HM E-
176 (T able 1). The major difference between the Beta varieties and the other two
varieties was that the two Beta varieties were triploids and the other two varieties were
diploids. In experiment two, leaf area, fresh weight, and dry weight of Beta 5736 were
reduced by micro-rate treatments and Hilleshog E-17 again did not have a significant
reduction in leaf area or biomass, confirming the results from the first experiment.
However, the fresh weight, dry weight, and leaf area of two triploids Spartan and Beta
5451 were not significantly reduced by micro-rate treatments (Table 2). Two diploids,
Hilleshog E-38 and Hilleshog RH-5, had significant reductions in all measured variables.
Six diploids including Prompt, Hilleshog E-33, Hilleshog E-38, Hilleshog RH-5 ACH 913,
ACH 1353, and USH 20 had dry weight reductions compared to their respective controls.
The USDA lines WC 93406, WC 93407, and WC 93409 showed significant reductions in
leaf area and dry weight compared to the untreated control in the growth chamber (Table
4). The only variable reduced with the USDA line WC 93404 was dry weight. Therefore
sugarbeet response to POST applied herbicides did not segregate by ploidy level or by
seed company.
Field research. In the field, the leaf area of five triploids: Beta 5736, Beta 5451, Beta
5172, ACH 185, and Spartan were reduced by 30, 38, 32, and 30%, respectively.
However, this was not statistically significant. The leaf dry weights of Beta 5736, Beta
5451, Beta 5172, and ACH 185 were reduced by the micro-rate applications (Table 3).

The leaf area of diploids was reduced by up to 40% but this was not statistically

 

‘ Beta seeds, 1788 Maschall Road, Shakopee, MN 55379.
5 American Crystal Sugar Company, 101 N. 3rd St. Moorhead, MN 56560.
6 Hilleshog seeds, 1350 Kansas Ave., Longmount, CO 80501.

73

significant. Dry weights of the diploids Hilleshog E-33, Hilleshog E-38, ACH 963, and
USH 20 were reduced by herbicide treatments (Table 5). The only diploids without
significant reductions in dry weights were Hilleshog E-17, Hilleshog RH-5, Prompt, ACH
913, and ACH 1353. These results are similar to the growth chamber results for Hillshog
E-17, but not for Prompt, ACH 1353, and ACH 913. The only significant reductions in
the four USDA lines were the leaf dry weights of WC 93407 and WC 93409.

Although some of the results differed between the growth chamber and the field,
the leaf fresh and dry weight of Hilleshog E-17 were not significantly reduced by the
micro-rate herbicide applications in the growth chamber or the field (Table 5).
Furthermore the leaf fresh and dry weights of Beta 5736 were reduced in the growth
Chamber and in the field. The Beta Seed Co. is presently replacing Beta 5400 and Beta
5736 with Beta 5451 and 5172. These data indicate that the newer varieties appear to
be less sensitive to micro-rate herbicide applications. Furthermore, the Hilleshog Seed
Co. is replacing E-17, with E33 and E38. These data indicate that their newer varieties
appear to be more sensitive to micro-rate treatments. However, it is difficult to draw
conclusions from one seed lot of each of these varieties. Further work should compare
seed lots and seed processing to determine how these factors affect emergence, stress
and herbicide response, and yield. Perhaps the seed lots of E-33 and E-38 tested were
more sensitive than seed produced in 2002 for the 2003 growing season. Since
sugarbeet seed harvest, handling, and processing are such critical components of seed
emergence, the influence of these factors versus the genetics of the variety on herbicide
response is difficult to assess. Varieties vary in emergence from year to year suggesting
that some varieties are affected by environmental conditions more than others. Seed
processing affects emergence, and some sugarbeet growers purchase raw seed and
some purchase pelleted seed. Seed quality is something that may not be adequately

controlled, but it would be beneficial to know how varieties are affected by seed harvest

74

and processing, as well as by field conditions including herbicide applications. Clearly
differences in Hilleshog E17 and Beta 5736 response to POST applied herbicides may
occur in future varieties.

Furthermore, it is difficult to determine how each variety metabolizes the four
herbicides applied in the micro-rate. The micro-rate applied to each variety contained
desmedipham, phenmedipham, triflusulfuron, and clopyralid. Desmedipham and
phenmedipham inhibit photosynthesis by binding to the Qe-binding niche on the D1
protein of the photosystem II complex in chloroplast thylakoid membranes (Vencill 2002);

triflusulfuron inhibits acetolactate synthase (ALS), a key enzyme in the biosynthesis of

 

the branched-Chain amino acids isoleucine, Ieucine, and valine (Vencill 2002); and the
mechanism of action of Clopyralid is not completely understood, but is similar to that of
endogenous auxin and other auxin-type herbicides (Vencill 2002). Each variety may
respond differently to each of the applied modes of action, and thus respond to a micro-
rate application may be confounded by applying herbicides with multiple modes of

action.

75

 

LITERATURE CITED

Dexter, A. G. and J. Kern. 1978. Response of sugarbeet varieties to Eptam and
Betanex, 1976 to 1978. Sugarbeet Res. Ext. Rep. 9:67-69.

Dexter, A. G. and J. L. Luecke. 1997. Interaction of sugarbeet varieties and
postemergence herbicides, 1996-1997. Sugarbeet Res. Ext. Rep. 28:88-102.

Smith, G. A., and E. E. Schweizer. 1983. Cultivar X herbicide interaction in sugarbeet.
Crop Sci. 23:325-328.

Smith, J. A., L. W. Panella, and C. D. Yonts. 2001. Seed and varieties in Sugarbeet
production guide. University of Nebraska Cooperative Extension. EC01-156. 9 p.

Schweizer E. E. and A. G. Dexter 1987. Weed control in sugarbeets (Beta vulgaris) in
North America. Rev. Weed Sci. 1987. 32113-133

Wilson, R. G. 1999. Response of nine sugarbeet (Beta vulgaris) cultivars to
postemergence herbicide applications. Weed Technol. 13:25-29.

Wilson, R. G., D. Yonts, and J. A. Smith. 2002. Influence of glyphosate and glufosinate
on weed control and sugarbeet (Beta vulgan's) yield in herbicide-tolerant
sugarbeet. Weed Technol. 16:66-73.

Vencill, W. K. 2002. Herbicide Handbook. 8'“ ed. Lawrence, KS: Weed Science Society
of America. p. 66, 87, 233, 300.

76

 

Table 1. Fresh weight, dry weight, and leaf area of four commercial sugarbeet varieties

following three micro-rate herbicide treatments in the growth chamber”.

 

 

Ploidy Leaf
Variety level Herbicide fresh weight dry weight Leaf area
reduction reduction reduction
9 — °/o — g — % — cm2 — % —
Beta Triploid Treated 117* 26 0.51* 35 61* 24
5400 Untreated 148 0.78 80
Beta Triploid Treated 98* 30 0.39* 43 49* 35
5736 Untreated 140 0.69 75
ACH Diploid Treated 133 2 0.67 1 1 72 14
555 Untreated 136 0.75 84
HM Diploid Treated 130 7 0.69 17 69 14
E-17 Untreated 140 0.83 80

 

“Indicates significant differences between means within varieties and columns

according to Tukey’s test for honestly significant differences (HSDoos) from an ANOVA.
bHerbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha
plus triflusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg aelha and M80 at 1.5%

WV.

77

Table 2. Fresh weight, dry weight, and leaf area of fourteen commercial sugarbeet

varieties following three micro-rate herbicide treatments in the growth chamber”.

 

 

 

Ploidy Herbicide Leaf Leaf
Variety level fresh weight dry weight Leaf area
reduction reduction reduction
9 — °/o— g — %— cm2 — %"—
Spartan Triploid Treated 16.0 18 1.1 31 350 13
Untreated 19.5 1.6 401
Beta Triploid Treated 17.3 10 1.1 27 367 8
5451 Untreated 19.3 1 .5 399
Beta Triploid Treated 13.3 32 0.8* 43 31 1 10
5172 Untreated 19.7 1.4 347
Beta Triploid Treated 12.1* 38 0.8* 43 263* 24
5736 Untreated 19.7 1 .4 347
ACH Triploid Treated 16.2 28 1.0* 44 358* 17
185 Untreated 22.4 1 .8 432
HM Diploid Treated 16.3 13 1.3 19 378 3
E17 Untreated 18.8 1.6 389
HM Diploid Treated 15.0 20 0.9* 47 322 16
E-33 Untreated 18.8 1 .7 382
HM Diploid Treated 13.3* 43 0.8* 55 292* 27
E-38 Untreated 22.3 1 .8 399
HM Diploid Treated 10.9* 45 0.7* 59 253* 27
RH-5 Untreated 20.0 1 .7 348
Prompt Diploid Treated 15.3 22 1.1* 39 326 16
Untreated 19.5 1.8 386
ACH Diploid Treated 16.9 13 1.0 33 320 16
963 Untreated 19.5 1 .5 382
ACH Diploid Treated 14.0 31 0.9* 44 297* 21
913 Untreated 20.4 1 .6 377
ACH Diploid Treated 14.1* 26 0.9* 44 314 18
1353 Untreated 19.0 1.6 381
USH 20 Diploid Treated 15.0 12 1.0* 37 331 9
Untreated 17.1 1 .6 365

 

a*lndicates significant differences between means within varieties and columns
according to Tukey’s test for honestly significant differences (HSDoos) from an ANOVA.
bHerbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha
plus triflusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg aelha and methylated
seed oil at 1.5% v/v.

78

 

Table 3. Fresh weight, dry weight, and leaf area of fourteen commercial sugarbeet

varieties following three micro-rate herbicide treatments in the field“.

 

 

Ploidy Leaf Leaf
Variety level Herbicide fresh weight dry weight Leaf area
reduction reduction reduction
9 — %— g — %— cm2 — %—
Spartan Triploid Treated 50 43 5.6 44 925 38
Untreated 88 1 0 1497
Beta Triploid Treated 51 44 5.4* 43 967 38
5451 Untreated 91 9.5 1572
Beta Triploid Treated 43 34 4.8* 32 812 32
51 72 Untreated 65 7.1 1 186
Beta Triploid Treated 54 29 5.9* 29 900 30
5736 Untreated 76 8.3 1282
ACH Triploid Treated 47 34 5.5* 30 883 30
185 Untreated 71 7.9 1262
HM Diploid Treated 33 42 3.8 43 628 40
E-17 Untreated 57 6.7 1042
HM Diploid Treated 40 38 4.2* 42 742 35
E-33 Untreated 65 7.3 1 148
HM Diploid Treated 36 35 4.2* 33 715 29
E-38 Untreated 55 6.3 1014
HM Diploid Treated 46 22 5.1 20 780 23
RH-5 Untreated 59 6.4 1017
Prompt Diploid Treated 42 32 4.9 32 783 27
Untreated 62 7.2 1080
ACH Diploid Treated 45 32 5.1* 32 833 19
963 Untreated 66 7.5 1029
ACH Diploid Treated 63 1 5 6.8 1 1 1205 1 1
913 Untreated 74 7.6 1352
ACH Diploid Treated 56 8 6.3 2 1082 3
1353 Untreated 61 6.4 1 1 1 1
USH 20 Diploid Treated 53 35 5.9* 37 945 29
Untreated 82 9.3 1335

 

a*lndicates significant differences between means within varieties and columns

according to Tukey’s test for honestly significant differences (HSDo_05) from an ANOVA.
bHerbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha
plus triflusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg aelha and methylated

seed oil at 1.5% WV.

79

Table 4. Fresh weight, dry weight, and leaf area of four USDA sugarbeet lines following

three micro-rate herbicide treatments in the growth chamber and in the field”.

 

 

Ploidy Leaf Leaf
Linec level Herbicide fresh Weight dg weight Leaf area
reduction reduction reduction
9 — % — g — % — cm2 — % —
Growth chamber studies
WC Diploid Treated 12.7 27 0.9* 47 290 20
93404 Untreated 17.5 1 .7 362
WC Diploid Treated 1 1* 41 0.8* 50 255* 27
93406 Untreated 18.7 1.6 348
WC Diploid Treated 1 1 .5* 44 0.8* 53 274* 29
93407 Untreated 20.7 1 .7 384
WC Diploid Treated 10 43 0.7* 50 225* 28
93409 Untreated 17.6 1 .4 314
Field studies
WC Diploid Treated 40 38 6.5 16 785 31
93404 Untreated 65 7.7 1 137
WC Diploid Treated 39 1 5 5.1 12 873 1
93406 Untreated 46 5.8 879
WC Diploid Treated 39 46 4.5* 48 742 46
93407 Untreated 72 8.6 1 377
WC Diploid Treated 35 48 4.2* 47 683 44
93409 Untreated 67 7.9 1220

 

a“Indicates significant differences between means within varieties and columns
according to Tukey’s test for honestly significant differences (HSDo_05) from an ANOVA.
bHerbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha
plus triflusulfuron at 0.004 kg ai/ha plus clopyralid at 0.023 kg aelha and methylated
seed oil at 1.5% v/v.

cWC 93404 (SP85576 cmc X 93H525), WC 93406 (SP85657 cms X 92H525), WC
93407 (FC607 cms X 92H525), WC 93409 (C40 X 92H526).

80

Table 5. Leaf area and dry weight reductions following three herbicide applications of 16

sugarbeet varieties in the growth chamber and in the field”.

 

 

 

 

Leaf area reduction Leaf dry weight reduction
Variety Ploidy level —Exp. 1 Exp. 2 Field Ep. 1 Exp. 2 Field
Beta 5400 Triploid * - - * - -
Beta 5736 Triploid * * NS * * *
Beta 5451 Triploid - NS NS - NS *
Beta 5172 Triploid - * NS - * *
ACH 185 Triploid - * NS - * *
Spartan Triploid - NS NS - NS NS
Hilleshog E-17 Diploid NS NS NS NS NS NS
Ach 555 Diploid NS - - NS - -
Prompt Diploid - NS NS - * NS
Hilleshog E-33 Diploid - NS NS - * *
Hilleshog E-38 Diploid - * NS - * *
Hilleshog RH-5 Diploid - * NS - * NS
ACH 963 Diploid - NS NS - NS *
ACH 913 Diploid - * NS - * NS
ACH 1353 Diploid - NS NS - * NS
USH 20 Diploid - NS NS - * *

 

a*lndicates significant differences between means within varieties and columns
according to Tukey's test for honestly significant differences (HSDogs) from an ANOVA, -
indicates that the specific variety was not included in that specific experiment, and NS
indicates no significant differences between means within varieties and columns.
bHerbicides applied were desmedipham plus phenmedipham (1 :1 ratio) at 0.09 kg ailha
plus trifiusulfuron at 0.004 kg ailha plus clopyralid at 0.023 kg aelha and methylated
seed oil at 1.5% WV.

81

EXTENSION SUMMARY OF WEED MANAGEMENT SYSTEMS IN SUGARBEET

Applying herbicides at a micro-rate every 97 GDD (max + min temperature/2 -
1.1 C = GDD/day C) controlled common lambsquarters and redroot pigweed in the
growth chamber and the field. Applying a micro-rate herbicide treatment every 97 GDD
(175 GDD F) increased the time between applications by one to three days compared to
micro-rate herbicide applications every 7 d in 2001 and 2002. Applying micro-rate
herbicide treatments every 125 GDD (225 GDD F) resulted in weed control similar to the
7 d timing and caused less sugarbeet injury than the 7 d or 97 GDD application timings.
When the micro-rate herbicide treatment was applied every 152 GDD (275 GDD F),
common lambsquarters control was acceptable; however, Amaranthus spp. control was
reduced compared to more frequent application timings. We would recommend applying
a micro-rate herbicide treatment every 152 GDD (C) early in the season (April to mid
May) when early season weeds such as common lambsquarters, common ragweed
(Ambrosia artemisiifolia L.), and velvetleaf (Abutilon theophrasti Medicus) are emerging,
and then switching to 125 or 97 GDD timings when Amaranthus spp. starts to emerge.
Annual grasses can be controlled by adding clethodim or quizalofop to all or one of the
micro-rate herbicide treatments.

Preemergence (PRE) herbicides increased common lambsquarters and
Amaranthus spp. control by 2 to 11% in 2001 and 2002. In 2002, PRE herbicides
increased sugarbeet injury by 10 to 15% when combined over postemergence (POST)
herbicides. This probably occurred because of cool-wet conditions early in the season in
2002. PRE herbicides such as cycloate or s-metolachlor will control yellow nutsedge
(Cyperus esculentus L.) Cycloate also provides good control of velvetleaf. If a field is
infested with yellow nutsedge and velvetleaf, PRE herbicides should be applied because
POST herbicides do not control yellow nutsedge and velvetleaf is difficult to control with

only triflusulfuron. Depending on which PRE herbicide is selected, the cost is similar to

82

 

or greater than the cost of one or more POST micro-rate herbicide applications. With
pyrazon, ethofumesate, or the combination of pyrazon and ethofumesate, the cost is
similar to two or more micro-rate herbicide applications. The registration of s-
metolachlor in 2003 and the expected registration of dimethenamid in 2004, along with
the registration of generic forms of ethofumesate may reduce the cost of PRE herbicides
in sugarbeet. So each sugarbeet grower will have to weigh the cost of a PRE herbicide
with the cost of an application of a micro-rate or standard-split POST herbicide
treatment.

In this research, desmedipham plus phenmedipham or desmedipham plus
phenmedipham plus ethofumesate applied in the micro-rate or standard-split in
combination with triflusulfuron and clopyralid provided similar weed control and
sugarbeet injury. In other research, micro-rate applications of desmedipham plus
phenmedipham plus ethofumesate have provided less sugarbeet injury and Amaranthus
spp. control. Micro-rate herbicide applications provide greater control of velvetleaf than
standard-split applications, because the methylated seed oil used in the micro-rate
increases the effectiveness of triflusulfuron. For both micro-rate and standard-split
applications, the timing of the first herbicide application is very important. Herbicides
need to be applied when weeds, particularly common lambsquarters, Amaranthus
species, and velvetleaf are in the cotyledon to- two- leaf growth stage.

This research indicated that sugarbeet varieties respond differently to herbicide
treatments. Hilleshog E-17 has been the leading variety in Michigan for several years
because of its’ early season vigor. However, E-17 lacks disease resistance so some
sugarbeet growers plant other varieties such as Beta 5736. In this research, the leaf dry
weight of E-17 was not significantly reduced by three micro-rate herbicide applications,
when measured 1 week after the last application. However, the leaf dry weight of Beta

5736 was significantly reduced in all three experiments. Beta 5736 is one of the leading

83

 

sucrose-producing varieties in Michigan. Therefore, early season leaf injury may not
result in sucrose yield loss. Breeding for resistance or tolerance to POST herbicides
would be difficult, because POST herbicide applications usually are combinations of
three or more herbicides with multiple modes of action. The response of each sugarbeet
variety to any stress including herbicides may depend on the growing conditions of the
seed plants, how the seed was handled, conditioned, and stored, and the environmental
conditions at planting, through the time of sugarbeet emergence, and at the times of
herbicide applications.

Since the phenotype expressed each year is a function of the genotype and the
environment, it may be that the environment is playing a key role in sugarbeet variety
response to POST herbicides and other stresses each year. Growers will continue to
choose varieties based on sucrose yield and disease resistance. How varieties respond
to early season stress, including herbicide applications is an area of future research.
Sucrose synthesis may not be delayed by early season stress and reductions in leaf

area or dry weight.

84

 

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