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thesis entitled

INTERSEEDED COVER CROPS IN SEED CORN PRODUCTION:
WEED CONTROL AND HERBICIDE TOLERANCE

presented by

Brent E. Tharp

has been accepted towards fulﬁllment
of the requirements for

Master of Sciengﬁegﬁmin Crop and Soil Sciences

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MSU In An Afﬁrmative Action/EM Oppomnlty Intuition
Mm:

INTERSEEDED COVER CROPS IN SEED CORN PRODUCTION:
WEED CONTROL AND HERBICIDE TOLERANCE

By

Brent E. Tharp

A THESIS
Submitted to
Michigan State University

in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Crop and Soil Sciences

1997

ABSTRACT

INTERSEEDED COVER CROPS IN SEED CORN PRODUCTION:
WEED CONTROL AND HERBICIDE TOLERANCE

By

Brent E. Tharp

Field studies were conducted in 1995 and 1996 to determine the effect of
interseeded cover crops on grass weeds. Cover crop treatments containing annual
ryegrass reduced the density of grass weeds 75 days after seed corn planting. However,
differences in visual grass control among cover crop treatments were not apparent at corn
harvest. Additional ﬁeld studies were conducted in 1995 and 1996 to determine the most
appropriate time to seed annual ryegrass and crimson clover following an application of a
preemergence herbicide. Annual ryegrass was not successfully established following
metolachlor, but was successfully established at an interval of time following an
application of EPTC and pendimethalin. Crimson clover was not successfully established
when it was seeded the same day herbicides were applied, but was successfully
established at an interval of time following an application of pendimethalin, EPTC and

metolachlor.

ACKNOWLEDGEMENTS

I would like to thank the members of my graduate committee, Dr. Richard
Harwood, Dr. Doug Landis, and Dr. Jim Kells for their insight and contributions to my
research. A special thanks goes to Dr. Jim Kells for the support, advice, and time he has
invested, and is continuing to invest in my graduate studies.

A sincere thanks goes to Andy Chomas, Corey Ransom, Jason Fausey, Eric
Spandl, Christy Sprague, Matt Rinella, Joe Simmons, and John Burk for their assistance
in the ﬁeld and greenhouse, and their tolerance of my “joyful” moods in the mornings. I
thank Joe Paling and Dale Mutch for the use of equipment, and enough thanks cannot be
expressed to Henry Miller who provided both equipment and land. I express my
appreciation for the friendships and times I have shared with the above mentioned people
in addition to Kelly Nelson, Bob Starke, Jeff Stachler, Gary Powell, Julie Lich, James
Mickelson, and Karen Novosel.

Finally, I cannot thank my parents enough for the love, support, and

encouragement they have provided.

iii

TABLE OF CONTENTS

PAGE
LIST OF TABLES ................................................... vi
CHAPTER 1. Review of Literature
Introduction ..................................................... 1
Cover Cropping Systems
Catch crop ................................................ 2
Smother crop .............................................. 3
Green manure .............................................. 3
Living mulch .............................................. 4
Winter cover crops .......................................... 5
Spring seeded .............................................. 7
Interseeded/Overseeded ...................................... 8
Weed Control with Cover Crops
Allelopathy ............................................... l 1
Weed control in cover crop residues ........................... 12
Weed control in live cover crops .............................. l3
Seed Corn Production ............................................ 14
Literature Cited ................................................. 19

CHAPTER 2. Evaluation of Interseeded Cover Crops for Suppression of Grass

Weeds in Seed Corn Production
Abstract ....................................................... 29
Introduction .................................................... 31
Materials and Methods ............................................ 32
Results and Discussion
Cover crop injury .......................................... 35
Grass weed suppression from cover crops ....................... 36
Layby applications of metolachlor ............................. 37
Seed corn yields ........................................... 37
Literature Cited ................................................. 39

iv

TABLE OF CONTENTS (cont)

CHAPTER 3. Potential Use of Corn Herbicides in Annual Ryegrass and Crimson
Clover Cover Cropping Systems

PAGE

Abstract ....................................................... 47

Introduction .................................................... 49
Materials and Methods

Greenhouse trials .......................................... 50

Field trials ............................................... 52
Results and Discussion

Greenhouse preemergence herbicide trials ...................... 53

Greenhouse postemergence herbicide trials ...................... 55

Field trials ............................................... 56

Annual ryegrass ﬁeld trials .................................. 56

Crimson clover ﬁeld trials ................................... 57

Literature Cited ................................................. 58

LIST OF TABLES

CHAPTER 2. Evaluation of Interseeded Cover Crops for Suppression of Grass

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Weeds in Seed Corn Production

PAGE
Dates of ﬁeld operations and experimental measurements .A ....... 41
Rainfall and irrigation amounts during an 11 week period
of the 1995 and 1996 growing season ........................ 42
Effect of preemergence herbicides on cover crop density and
days after seed corn planting, 1995 and 1996 .................. 43
Effect of cover crops on grass weed density 75 days after seed
corn planting and grass weed control 112 days aﬂer seed corn
planting, 1995 and 1996 ................................... 44
Effect of layby metolachlor applications on grass control 112
days after seed corn planting, 1995 and 1996 .................. 45
Effect of cover crops on seed com yield, 1995 ................. 46

CHAPTER 3. Potential Use of Corn Herbicides in Annual Ryegrass and Crimson

Table 1.

Table 2.

Table 3.

Table 4.

Clover Cover Cropping Systems

Rainfall amounts during a 13 week period of the 1995
and 1996 growing season .................................. 60

Cover crop seeding dates .................................. 61

Effect of preemergence herbicides on grass cover crop species
28 days after treatment .................................... 62

Effect of preemergence herbicides on legume cover crop species
28 days after treatment .................................... 63

LIST OF TABLES (cont)

PAGE
CHAPTER 3. (cont)

Table 5. Effect of postemergence herbicides on grass cover crop

species 14 days after treatment ............................. 64
Table 6. Effect of postemergence herbicides on legume cover crop

species 14 days after treatment ............................. 65
Table 7. Effect of preemergence herbicides on annual ryegrass 30 days

various seeding times in 1995 .............................. 66
Table 8. Effect of preemergence herbicides on crimson clover 30 days

various seeding times in 1995 .............................. 67

vii

CHAPTER 1
Review of the Literature

Introduction. Cover crops offer “many potential beneﬁts to agriculture production
systems. They can reduce water and wind erosion (Smith et al. 1987; Frye et al. 1983;
Pieters and McKee 1938), sequester excess nitrates (Shipley et al. 1992; Jackson et al.
1993), provide nitrogen to succeeding crops (Wilson and Hargrove 1986; Wagger 1989;
Mitchell and Teel 1977), improve soil properties (Hoyt and Hargrove 1986; Benoit et al.
1962), provide a favorable enviromnent for predatory insects (Clark et al. 1993; Bug
1990; Kaakeh and Dutcher 1993), and suppress weeds through allelopathy, competition,
and/or physical effects (Lal et a1. 1991). The suppression of weeds has been
demonstrated with cover crop residues and live cover crop plants (W orsham 1991).
Weed management, in agronomic production systems requires a signiﬁcant
amount of time, energy, and resources. In seed corn production, growers will often use a
combination of herbicides and cultivation to reduce the level of weeds. This management
system has not been consistently effective, particularly with weeds which emerge late in
the growing season. Many of the management practices associated with seed corn
production, such as detasseling and irrigation, create a favorable environment for weed
infestation. A cover crop seeded after corn emergence might compete enough with late
emerging weeds to provide sufﬁcient suppression of the weeds. This type of cover
cropping system is known as interseeded or overseeded cover crops. Many times

1

2
interseeding cover crops will follow a previous herbicide application. Little information
is available regarding the susceptibility of cover crop species to commonly used
herbicides. The research contained in this thesis will encompass the use of interscedcd
cover crops to reduce annual grass infestation in seed corn, and review the potential use

of corn herbicides in cover crops.

Cover Cropping Systems

Numerous terms in literature are used to describe cover cropping systems. Some
terms describe the way cover crops are used: catch crop, smother crop, and green manure.
Other terms are an actual description of the cover cropping system: living mulch and
winter cover crop, while some terms describe how the cover crops are established: spring
seeded, interseeded, or overseeded. All of these terms are accurate descriptions of cover
cropping systems, and many times the terms can be used interchangeably.
Catch crop. A catch crop is usually made in reference to a cover crop which has been
established in order to sequester excess nutrients, primarily nitrates. In agriculture,
nitrogen fertilizer is often applied in amounts which exceed crop requirements. The
excessive amounts of nitrogen often result in nitrate contamination of groundwater
(Baker and Johnson 1981; Angle et al. 1993; Roth and Fox 1990). Many studies have
shown cover crops can be used to reduce the levels of nitrate contamination (Martinez
and Guiraud 1990; Staver and Bronsﬁeld 1990; Jackson et a1. 1993; Eisenbeis 1994).
The cover crop should be established near maturity of a row crop, yet early enough to

allow sufﬁcient biomass accumulation. Uptake of nitrates will continue as the cover

3

crops accumulate biomass. Martinez and Guiraud (1990) and Staver and Bronsﬁeld
(1990) reported that annual ryegrass (Lolium multzﬂorum) and cereal rye (Secale cereale
L.) removed large amounts of nitrates ﬁ'om the soil proﬁle. Shipley et a1 (1992)
concluded that grass cover crops conserved more residual nitrogen than legumes. Cover
crops may effectively remove nitrates, however they eventually release nitrates and
additional nutrients (Miller et al. 1994). The eventual release of sequestered nutrients
should be considered when a catch crop is going to be used. Research has been
conducted investigating the release of nitrogen ﬁbm cover crop residues, and how the
release could correspond to an actively growing crop (Dan 1995; Wilson and Hargrove
1986; Wagger 1989a).

Smother crop. The term smother crop is primarily used in reference to a cover crop that
is used for the purpose of weed control. Smother crops can control weeds through
physical competition for light and water, and through the inhibitory action of allelopathic
substances (Overland 1966; DeHaan et al. 1994). A more comprehensive discussion on
the use of cover crops for weed control will be included in a latter section of this
literature review.

Green manure. Pieters and McKee (1938) differentiated between a cover crop and a
green manure crop. They described the function of a cover crop “to prevent erosion and
leaching, to shade the ground, or to protect the ground ﬁ'om excessive freezing and
heaving.” Their description of the function of a green manure was “to add organic matter
to the soil. As an incident to this function the nitrogen supply of the soil may be increased

and certain minerals made more readily available, these effects in turn increase the

productivity of the soil”.

Living mulch. In a living mulch/row crop system, the living mulch is established prior
to row crop establishment, and the row crop is established directly into all or a portion of
a suppressed or actively growing cover crop species.

Many of the ﬁeld trials involving living mulch systems have focused on weed
control, management of the mulches, and the effect of the mulches on the associated row
crop. Field trials using grass and legume mulches in no-till corn production have
revealed comparable com yields are achievable depending on the species of mulch used
(Elkins et al. 1983; Echtenkarnp and Moomaw 1989). Elkins et al. (1983) showed good
corn yields could be obtained while maintaining up to 60% of a living mulch.
Turfgrasses and legumes were investigated for use as living mulches in sweet corn
production at Cornell University (Nicholson and Wien 1983; Vrabel et al. 1980).
Chewing fescue (F estuca rubra L.), Kentucky bluegrass (Poa pratensis L.), and ‘Kent’
white clover (Trifolium repens L. ‘Kent’) did not adversely affect the yield of sweet corn.
However, other species have been reported to decrease corn yields (Echtenkamp and
Moomaw 1989; Nicholson and Wien 1983,). The use of living mulches is not just
conﬁned to the United States. Akobundu and Okigbo (1984) reported the successful use
of a living mulch system in maize production in Nigeria.

Some investigators have tested the use of perennial legumes as living mulches.
Hartwig (1990) has investigated crownvetch (Coronilla varia L.) living mulch systems,
while Illnicki and others (Illnicki and Enache 1992; Illnicki and Vitolo 1986) have

investigated the use of subterranean clover (Tn'folium subterranean: L.). Research

5
conducted by Ranells and Wagger (1992) and Kumwanda et a1 (1993) have focused on

developing an annual legume, crimson clover (Tnfolium incamatum L.), into a perennial
living mulch system.
Winter cover crops. A winter cover cropping system should provide ground cover
throughout the winter season. Winter cover crops can be established while a row crop is
growing, but are often established after the row crop has matured or has been harvested.
This system is similar to a living mulch system except that the plants are destroyed, either
by chemical or mechanical means or by natural winterkill. The remaining residues are
often left as a mulch, and the row crop is no-till planted directly into the mulch.
Compounds, which are potentially phytotoxic to crops, are often released during
decomposition of the residues (Chase et al. 1991; White et al. 1989). Ifa sensitive crop is
going to be planted directly into a mulch, planting should be delayed at least two weeks
after the cover crop has been killed (Raimbault et al. 1991). Removal of cover crop
residues within the row combined with selected in-furrow treatments may reduce the
interval between cover crop destruction and row crop planting (Dabney et al. 1996).
Cereal rye is a p0pular winter cover crop species, and conﬂicting data exists
regarding the effects of a rye cover crop in corn production. Moschler et al. (1967)
reported that com yields were sometimes increased when com was grown in the presence
of a rye mulch. Soil moisture was also conserved in his ﬁeld trials. Decreased corn
yields was reported by Eckert (1988). He felt the decreased yields were a result of
reduced com populations in rye treatments, which is consistent with results published by

Mitchell and Teel (1977).

6

Legumes may be a better choice for a winter cover crop species and have been
shown to increase corn yields (Holderbaum et al. 1990; Decker et al. 1994; Smith et al.
1987; Torbert et al. 1996). Holderbaum et a1 (1990) concluded that nitrogen availability
will be reduced in legume/small grain cover cropping systems, because the small grain
will immobilize the nitrogen. Wagger (1989a) concluded that winter annual legume
cover crops are capable of providing a substantial portion of nitrogen to a succeeding
crop. In his ﬁeld trial the production of corn dry matter was higher for legume cover
crops as compared to a rye cover crop. Grain sorghum following a legume cover crop did
not respond to the addition of nitrogen fertilizer, but did respond to as much as 99 kg
N/ha when following a rye cover crop (Hargrove 1986). Winter cover cropping systems
using hairy vetch (Vicia villasa Roth.) have produced encouraging results (Clark et al.
1995; Frye and Blevins 1989). Scientists at the University of Kentucky have estimated
hairy vetch can supply the equivalent of 90-100 kg/ha of nitrogen fertilizer (Ebelhar et al.
1984; Blevins et al. 1990).

Many of the potential beneﬁts from winter cover cropping systems depend on
how the cover crops are managed prior to row crop planting. Emergence and growth of
corn and cotton were not effected when planted into soils containing legume residues;
however, the dry weight of corn was increased when the legume residue was placed on
the surface (White et al. 1989). Many scientists have investigated how nitrogen dynamics
are effected by management of cover crops (Wilson and Hargrove 1986; Wagger 1989b;
Karlen and Doran 1991). Dabney et al. (1991) investigated the use of mechanical

methods to manage cover crops, while other studies focused on management by chemical

7

means (Peters and Dest 1975; Weston 1990; Dabney and Grifﬁn 1987). Clark et al.
(1995) reported that grain yields were higher when hairy vetch was killed later in the
spring as compared to early killed hairy vetch. They concluded that soil water
conservation by late killed vetch mulches had a greater inﬂuence on com production than
vetch water use in the spring (Clark et al.1995). On the other hand, Munawar et al.
(1990) reported yields were signiﬁcantly greater with early killed rye than late-killed rye.
They believed allowing a cover crop to grow up to the time of corn planting may
adversely affect the subsequent corn crop by competing for soil water. However, they
also felt that during years of high spring rainfall, it may be advantageous to allow the
cover crop to grow longer in order to dry out the soil and produce more dry matter for
surface mulch, which would conserve more water for the corn crop during the summer
(Munawar et al.1990). Research conducted by Hesterman et al. (1992) revealed that the
yield of corn following a winter cover crop increased when soil water was adequate at the
time of corn planting. However, when spring precipitation was below normal the yield of
corn following a winter cover crop was reduced (Hesterman et al. 1992).

Soil temperature under a mulch is another important factor to consider when using
a winter cover crop. Fortin and Pierce (1991) reported that com development was
delayed when soil temperatures under the mulches were 2.2°C lower than bare soil
temperatures.
Spring seeded. Spring seeded cover crops are established from late winter up to planting
of a row crop. Many species of cover crops have been successfully established in the

spring (Nelson et al. 1991). In an evaluation of multiple establishment periods, Stute and

8

Posner (1993) found that cover crops which were established in the spring had the largest
amount of biomass. Spring planted rye resulted in lower or comparable soybean yields in
a ﬁeld trial in Minnesota (Wames et al. 1991). Ateh and Doll (1996) believed rye could
be planted in the spring without a reduction in soybean yield if weed pressure was low,
ground cover and soil moisture were adequate, and rye interference was minimal.
DeHaan et al. (1994) investigated multiple interference durations of spring seeded
yellow mustard in corn production. Using principles explained in previous wwd
interference studies, they believed it was possible that a spring seeded cover could reduce
weed populations and have only a small impact on corn yield. They reported that yellow
mustard gown with a corn crop for four weeks, and gown to a maximum height of 10
cm resulted in an average corn yield reduction of 4%.
Interseeded/Overseeded. The terms interseeded and overseeded are used synonymously
throughout literature pertaining to cover crops. An interseeded crop is seeded directly
into a row crop. A potential problem associated with interseeded crops involves
competition between interseeded crops and row crops (Exner and Cruse 1993; Kurtz et a1.
1952). Competition is the relationship between two or more plants in which the supply of
a gowth factor falls below their combined demands (Aldrich 1984). A crop gowing
between the rows of another crop will compete for nitrogen and water (Kurtz et al. 1952).
Much of the literature pertaining to competition in row crops has dealt primarily with
weed/crop competition (Zimdahl 1980; Aldrich 1984; Schmenk 1994; Fausey 1996).
When giant foxtail was left to a height of at least 30.5 cm, corn yields were signiﬁcantly

reduced due to the competitive effects of giant foxtail (Knake and Slife 1969). Corn

9

yields were signiﬁcantly reduced when giant foxtail was seeded the same day the corn
was planted (Knake and Slife 1965). Hall et al. (1992) reported that the critical period of
a weed free environment began between 3-14 leaf corn and ended on average at 14 leaf-
stage corn. Therefore, it would be possible to establish an interseeded crop in a row crop
production system without sacriﬁcing yield of the row crop. Based on the results of
competition studies, the most appropriate time to seed an interseeded crop would be at
some point after row crop planting.

Early research involving interseeded crops focused primarily on establishment of
the crops for the purpose of forage production (T esar 1957; Pendleton et al. 1957; Hayes
1958; Nordquist and Wicks 1974). Recent research of interseeded systems has focused
on using interseeded species as cover crops rather than forages. The primary objective
for much of the interseeded cover crap research has focused on how cover crop species
. affect the row crop; whereas, with an interseeded forage system, much of the research
focused primarily on the performance of the forage crop. Although the results of
interseeded forage studies might be based on a slightly diﬁ'erent objective, the results of
forage research can be directly applied to the management of interseeded cover crops.
For instance gass species tested by Hayes (1958) provided more cover than legumes. In
the ﬁeld trials of Pendleton et al. (1957), com yields decreased as the width between corn
rows increased, and a trend of lower yields occurred when alfalfa was interseeded
compared to clear seeded. Corn gain yields were reduced when alfalfa was seeded the
same day of corn planting and at the time of ﬁnal row cultivation, but the yield of the ﬁrst

cutting of alfalfa a year after seeding was highest when alfalfa was seeded the same day

10

of corn planting (Nordquist and Wicks 1974). Pendleton et al. (1957) mentioned that
when gowers are contemplating using an interseeded cropping system, they must ﬁrst
determine their objectives in order to properly choose their management practices.
Interseeded cover crops are seeded from the time of row crop establishment up to
the time of row crop harvest. The time of cover crop seeding is an important factor to
consider in an interseeded cover cropping system. Pendleton ct al. (1957) believed that
the earlier the interseeded crop was seeded the more likely yields would be reduced.
Corn yields were reduced when cover crops were seeded the same day of corn planting
(Exner and Cruse 1993; Vrabel et al. 1980); however, soybeans yields were not reduced
at this seeding time (Robinson and Dunharn 1954). Seeding cover crops near the time of
a ﬁnal inter-row cultivation is another popular time to establish interseeded cover crops,
and reduction in gain yields were not apparent when cover crops were seeded near this
time (Helsel et al. 1991; Scott et al. 1987; Nanni and Baldwin 1987; Eadie et al. 1992)
The effect of seeding time on cover crop establishment is dependent on species
and weather conditions (Exner and Cruse 1993; Palada et al. 1983; Keeling et al. 1996;
Vrabel et al. 1980). Small seeded cover crop species interseeded into cotton were more
dependent on rainfall than larger seeded species (Keeling et al. 1996). Ground cover
from the interseeded cover creps was usually geater than the treatments without a cover
crop (Stute and Posner 1993; Scott et al. 1987; Vrabel et al. 1980; Eadie et a1. 1992).
Scott and Burt (1987) reported that interseeded cover crops provided as much cover and
yielded as much forage as the cover crops which were seeded without a row crop.

Cover crops have been shown to provide a favorable habitat to both predatory and

l 1
pest insects (Bugg and Ellis 1990). Interseeding red clover (Tnfoliwn pratense) into a
corn crop reduced the level of corn damage by European corn borer (Ostrinia nubilalis
‘ Hﬁbner) (Lambert et al. 1987). The population of generalist predatory insects increased as
the amount of gound cover increased (Clark et al. 1993). Kaakeh and Dutcher (1993)
reported crimson clover and hairy vetch were preferential hosts to Acyr'thosiphon pisum
Harris, which is an alternate prey of generalists predators. Maintaining alternate prey on
cover crops could potentially attract higher densities of natural enemies (Bugg and

Dutcher 1989).

Weed Control with Cover Crops
Allelopathy. Putnam and Duke (197 8) deﬁned allelopathy as the detrimental effect of
higher plants of one species on the germination, gowth, or development of plants of
another species. The detrimental effect of allelopathy is exerted through release of
chemicals by the donor plant (Putnam and Duke 1978). Williams and Hoagland (1982)
have investigated the effects of phenolic compounds on germination of weed and crop
seed. Extracts of rye were shown to inhibit the germination and gowth of lettuce
(Lactuca setiva L.) (Power 1991) and bamyardgass (Echinochloa crus-galli L.) (Chase
et al. 1991), while effects on the germination and gowth of cucumber (Cucumis sativus
L.) and snap bean (Phaseolus vulgaris L.) were variable (Chase et al. 1991). Overland
(1966) reported the inhibition of common chickweed (Stellarr'a media L.) gowth and
germination from exposure to aqueous leachates of barley (Hordeum vulgare L.).

Aqueous extracts of wheat (Triticum aestivum L.) reduced the germination and gowth of

12

pitted momingglory (Ipomoea lacunosa L.) and common ragweed (Ambrosia
anemisiifolia L.) (Stutc and Poner 1993), while aqueous extracts of various legumes
inhibited the germination and gowth of corn (Zea mays L.), cotton (Gassypium
hirsutum), and wild mustard (Brassica kaber) (White et al. 1989). Shettel and Balke
(1983) applied ﬁve allelopathic chemicals at multiple timings and rates to a variety of
weed and crop species. Most of the chemicals applied preplant incorporated at rates as
high as 56 kg ha'1 reduced the gowth of corn, soybean, velvetleaf (Abutilon thoephrasti
Medic.), redroot pigweed (Amaranthus retroﬂexus L.), and wild proso millet (Panicum
miliaceum). Postemergence applications of caffeine and hydroquinone inhibited the
gowth of the weed species more than the crop species (Shettel and Balke 1983).
Weed control in cover crop residues. The management of allelopathic cover crop
residues is one way allelopathy could be used in cropping systems (Weston 1996).
Suppression of weeds have been demonstrated in many ﬁeld trials using cover crops
(Worsham 1991b; Einhellig and Leather 1988; Putnam et al. 1983; Gliessman 1983).
Allelochemicals, that are released from rye residues, can reduce weed seed germination
and seedling gowth (Barnes and Putnam 1987). Rye residues have been shown to be
phytotoxic to cress (lepidium sativum L.), lettuce, bamyardgass, and proso millet
(Panicum miliaceum L.) in a soil bioassay, and the phytotoxic compounds were
degadable (Barnes and Putnam 1986). Greenhouse and ﬁeld studies revealed that
residues from brassica cover crops reduced the gowth and emergence of some weed
species (Boydston and Al-Khalib 1994).

Hairy vetch residue suppressed the establishment of some weed species under

l3

shaded conditions more than under full srmlight conditions, suggesting light was a more
important factor than allelopathy or physical impedance (Teasdale 1993). In no-till corn
production, weed suppression by cover crops was variable (Teasdale and Daughtry 1993;
Hoﬂinan et al. 1993; Curran et al. 1994). Curran et al. (1994) concluded that differences
in early evaluations weed densities were geater than late evaluations of weed densities.
Teasdale et a1. (1991) reported a reduction of total weed density in rye or hairy vetch
residue, when the cover crop biomass exceeded 300 g/m and covered more than 90% of
the soil. Weed suppression occurred in hairy vetch and rye cover crops which were
mowed prior to no-till corn planting (Johnson et al. 1993; Mangan et al. 1995). However,
corn gowth and yield often suffered ﬁbm this strategy of cover crop management
(Johnson et al. 1993; Hoffman et al. 1993; Curran et al. 1994). Greater than 90% weed
control in rye mulch was reported in a no-till soybean production system (Liebel et al.
1992). Another soybean ﬁeld trial revealed inconsistent results of weed suppression
when rye, wheat, and triticale (X Triticosecale Wittmack ‘OAC Wintr’) cover crops were
used (Moore et al. 1994). In a strawberry (Fragarr’a x aranassa Duch.) production
system, rye and wheat mulch provided geater early season weed suppression than barley
(Hordeum vulgare L. ‘Barsoy’) (Smeda and Putnam 1988).

Weed control in live cover crops. Weed levels in an interseeded cover cropping system
were less than in a corn monoculture system (Mt. Pleasant and Scott 1991). Rye seeded
in the spring at 168 kg/ha reduced the biomass of weeds as compared to rye seeded at 56
kg/ha (Ateh and Doll 1996). A subterranean clover living mulch system provided

excellent weed control without the use of herbicides (Enache and Ilnicki 1990; Ilnicki and

l4

Enache 1992). Hartwig (1976) reported a reduction in the gowth of yellow nutsedge
(Cyperus esculentus) from a crownvetch living mulch. Living mulches in sweet corn
production eﬁ‘ectively suppressed weeds (DeGrcgorio and Ashley 1986; Vrabel et a1.
1980). A living mulch of ladino clover (Tnfolium repens L.) reduced the biomass of
weeds, but the yield of no-till sweet corn was also reduced (Galloway and Weston 1996).
Vrabel et a1. (1980) concluded weed suppression was better for earlier seeded cover
crops, but sweet corn yields were also reduced at this seeding time. A similar trend was
apparent with spring seeded yellow mustard; as the duration of interference increased
weed dry weights decreased and corn gain yields decreased (DeHaan et al. 1994).
Echtenkamp and Moomaw (1989) stated that a living mulch could control the gowth of
weeds, but could also compete with corn for soil water when rainfall is below normal. In
general, live cover cropping systems have the potential to suppress weeds, but yields of

the row crop are often reduced.

Seed Corn Production
Corn was an established crop in North America before the arrival of the ﬁrst
EurOpean explorers. Christopher Columbus once reported that his brother passed through
eighteen miles of corn, which had been raised by the Indians. The Indians taught the
early colonists how to raise corn and many of our modern corn varieties can be traced
back to the corn types obtained from the Indians (Bressman and Wallace 1949). The corn
raised in post colonial days were a result of random crosses of ﬂint, dent, and gourdseed

corn types (Bressman and Wallace 1949). The ﬂint-dent crosses became the predominant

15

crop raised in the midwest region of the United States, and a large portion of the midwest
eventually became known as the “corn belt”.

In the 1870's W. J. Beal of Michigan State University was one of the ﬁrst
scientists to work with controlled crosses. His research along with more in-depth
research of Dr. G. H. Shull and Dr. E. M. East at Connecticut eventually led to the
introduction of hybrid corn (Bressman and Wallace 1949). Hybrid corn is a cross of two
or more unrelated lines of corn, known as inbreds (Bickner 1993). The progeny of the
cross will often yield higher than the parent lines, and this enhanced performance is often
referred to as hybrid vigor (Sprague 1992). Hybrid vigor was a primary reason hybrid
corn was adopted in the United States. Before the introduction of hybrid corn, farmers
would choose corn seed ﬁom the previous year and then plant this seed the following
year. This process was known as open pollination (Bickner 1993). In 1933 about one
percent of the corn gown in the corn belt was a hybrid, and in 1955 nearly all corn gown
in the United States was a hybrid (Airy et al. 1961).

If seed ﬁom a hybrid is planted the succeeding year, the yield ﬁom the succeeding
crop will be reduced. Therefore, the use of hybrid seed requires the production of new
seed each year (Airy et al. 1961). An industry, comprised of both large and small
companies, has evolved which is responsible for the production of new hybrid seed. The
larger companies manage all aspects of seed corn production, ﬁom the development of
new inbreds to the ﬁnal sale of the hybrid seed. The large diversity of hybrids sold by
seed corn companies require maintenance and multiplication of parental inbred seed lines.

The inbred lines are the basic foundation of the commercial hybrids, hence the name

16
foundation seed (Craig 1977). Most foundation seed is gown in isolation, usually at
least 400m ﬁom other com (J ugenheimer 197 6), and is managed by trained technicians
(Steele 1978). These stringent measures are used in order to ensure genetic purity of the
foundation seed. Smaller seed companies will often purchase the foundation seed ﬁom
companies who specialize in foundation seed production (Craig 1977). Foundation seed
is used for producing hybrid commercial corn seed (Jugenheimer 1976). Foundation seed
is often gown by farmers under contract ageements with seed corn companies (Steele
1978). Most agonomic practices used in seed corn production such as fertilizing,
planting, and pest management are similar to commercial corn production, but are under
the supervision of the seed corn company (Wych 1988).

Many of the current commercial hybrids are a result of single crosses or modiﬁed
single crosses (Wych 1988). A single cross is the progeny of two inbred lines. One
inbred is used as the male pollen bearing parent, while the other inbred is used as the
female seed bearing parent. The two inbred parents are planted in the same ﬁeld and are
isolated from other com ﬁelds. An important aspect of seed corn production involves
assuring that an abundant supply of pollen is present when the female inbred is in the silk
stage. In order to ensure enough pollen is produced, male and female inbreds are often
planted in patterns of 4:1 (four rows of female to one row of male), 4:2, 4:1:4z2, 6:2, or
solid female with the male rows interplanted (W ych 1988). Techniques are also used in
order for the female and male parents to ﬂower on the same date, which is known as a
“nick”. These techniques could include clipping or ﬂaming the pollen parent, planting

the parents at different times, variable fertilizer rates, or different planting depths (Craig

17

1977). The pollen parent is often destroyed after pollination is complete, thereby
eliminating the possibility of seed contamination ﬁom the pollen parent (Craig 1977).

Another critical factor in seed corn production involves ensuring pollen of the
seed parent is not produced. Various methods for pollen control are utilized. These
include detasseling, cytoplasmic sterility, genie male sterility, and chemical pollen
control (Craig 197 7). The two most common methods are detasseling and cytoplasmic
male sterility (Wych 1988). Detasseling involves removal of the tassel ﬁom the seed
parent either manually or in combination with mechanical operations (W ych 1988).
Detasseling is ultimately the responsibility of the seed corn company (Steele 1978).

Seed com is often harvested when the seed has reached physiological maturity
(Wych 1988), which is typically much earlier than commercial corn harvest. The contract
grower is usually responsible for corn harvest (W ych 1988). The corn is generally
harvested on the ear, and transported to the seed corn facility where the corn is eventually
sorted, husked, dried, shelled, cleaned, sized, treated, and bagged (Wych 1988). During
all of these processes the corn is handled in such a manner as to minimize damage of the
corn seed, because damaged seed will result in reduced germination. The ﬁnal step in
seed corn production is selling the corn. Most seed corn companies will use a farmer-
dealer system in conjunction with their own sales staff (W ych 1988).

Although many of the agonomic practices for seed corn production are similar to
commercial corn production, the production of seed corn requires more intense
management inputs, and involves more risks. Inbred seed are inherently weak, emerge

later, and gow more slowly than many of the commercial hybrids. Smaller gowing

l8

inbreds, detasseling, and male corn row removal will reduce the competitiveness of the
corn, which is an important factor in weed control (Harvey 1994). Herbicides are heavily
relied on for weed control in the seed corn industry (Craig 1977), but not all herbicides
are safe on all inbreds (W idstrom and Dowler 1994; Green et al. 1997). Therefore, the

infestation of weeds is a major concern in seed corn production.

l9

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beneﬁts to corn: rotation vs ﬁeld-nitrogen effects. Agon. J. 88:527-535.

Vrabel, T. B., P. L. Minotti, and R D. Sweet. 1980. Seeded legumes as living mulches
in sweet corn. Proc. Northeastern Weed Sci. Soc. 34:171-175.

Wagger, M. G. 1989a. Cover crop management and nitrogen rate in relation to gowth
and yield of no-till corn. Agon. J. 81:533-538.

Wagger, M. G. 1989b. Time of dessication effects on plant composition and subsequent
nitrogen release ﬁom several winter annual cover crops. Agon. J. 81:236-241.

Wames, D. D., J. H. Ford, C. V. Eberlein, and W. E. Lueschen. 1991. Effects of a
winter rye cover crop system and available soil water on weed control and yield in
soybeans. p. 149-151. In W. L. Hargove (ed.) Cover crops for clean water. Soil and
Water Conserv. Soc., Ankeny, IA.

Weston, L. A. 1990. Cover crop and herbicide inﬂuence on row crop seedling
establishment in no-tillage culture. Weed Sci. 38:166-171.

Weston, L. A. 1996. Utilization of allelopathy for weed management in agoecosystems.
Agon. J. 88:860-866.

White, R. H., A. D. Worsham, and U. Blum. 1989. Allelopathic potential of legume
debris and aqueous extracts. Weed Sci. 37:674-679.

28

Widstrom, N. W. and C. C. Dowler. 1994. Maize inbred response to nicosulfuron.
Agon. Abs. ??

Williams, R D. and R. E. Hoagland. 1982. The effects of naturally occurring phenolic
compounds on seed germination. Weed Sci. 30: 206-212.

Wilson, D. O. and W. L. Hargove. 1986. Release of nitrogen ﬁom crimson clover
residue under two tillage systems. Soil Sci. Soc. Am. J. 50:1251-1254.

Worsham, A. D. 19913. Allelopathetic cover crops to reduce herbicide input. Proc.
Southern Weed Sci. Soc. 44:58-69.

Worsham, A D. 1991b. Role of cover crops in weed management and water quality. p.
141-145. In W. L. Hargove (ed.) Cover crops for clean water. Soil and Water Conserv.
Soc., Ankeny, IA.

Wych, R D. 1988. Production of hybrid seed com. p. 565-607. In G. F. Sprague and J.
W. Dudley (ed.) Corn and Corn Improvement. Agon. Monog. l8. ASA, CSSA, and
SSSA, Madison, WI.

Zimdahl, R. C. 1980. Weed crop competition. A Review Int. Plant Prot. Conf. Oregon
State Univ., Corvallis.

CHAPTERZ

Evaluation of Interseeded Cover Crops for Suppression of Grass Weeds in Seed

Corn Production

Abstract. Seed corn ﬁelds in southwest Michigan are often infested with high
populations of gass weeds. These gasses create harvesting dimculties and can reduce
corn yield. Studies were conducted in seed corn ﬁelds in St. Joseph County, Michigan in
1995 and 1996 to examine the potential of interseeded cover crops for suppression of
gass weeds. Dominant gass species were fall panicum in 1995 and large crabgass in
1996. Annual ryegass, crimson clover, and an annual ryegass + crimson clover mixture
were seeded over plots that were treated, at seed corn planting, with metolachlor or
EPTC. The cover crops were seeded when the seed corn was in the V4—V6 gowth stage.
Metolachlor was more injurious to annual ryegass than EPTC. Annual ryegass plots
following metolachlor had signiﬁcantly lower height and density compared to plots
following EPTC. Crimson clover following metolachlor were not reduced in density or
height. Grass weed densities were recorded 75 days after seed corn planting for cover
crop treatments which followed EPTC. The annual ryegass and the annual ryegass +
crimson clover mixture had lower gass weed density than where no cover crop was
seeded. Crimson clover alone did not signiﬁcantly reduce gass weed densities. Visual
ratings 112 days after planting revealed no apparent differences in gass control among

treatments seeded with cover crops or between cover crop treatments and plots with no

29

30

cover crop. Interseeded cover crops did not sufﬁciently control annual gass weeds.
Nomenclature: EPT C, S-ethly dipropyl carbamothioate; metolachlor, 2-chloro-N-(2-
ethyl-6-methylphenyl)-N-(2-methoxy-l-methylethyl)acetamide; fall panicum, Panicum
dichotomiﬂorum Michx. # PANDI; large crabgass, Digitaria sanguinalis (L.) Scop. #
DIGSA; annual ryegass, Lolium multtﬂorum L.; crimson clover, Trifolium incarnanim
L.#TRFIN;corn,ZeamaysL.

Additional index words: EPTC, metolachlor, cover crops, interseeded, overseeded, seed

corn production, layby herbicide application.

 

Abbreviations: DAP, days after planting.

3 1
INTRODUCTION

Seed corn production is a major agiculture industry in southwest Michigan. A
potential problem with this production system is the infestation of weeds. Weeds
compete with seed corn for water and nutrients, and can interfere in harvesting
operations. The management practices used in raising a crop of seed corn, such as
irrigation, removal of the male com row, and detasseling, create an ideal environment for
the establishment of weeds. Weeds also ﬂourish in seed corn production due to the
inherent weakness of inbred plants. Harvey and McNevin (1990) reported that the
amount of weed control in a vigorous ﬁeld corn crop was geater than in a less vigorous
sweet corn crop. Harvey (1994) suggested seedbed preparation, management of crop
competition, row cultivation, rotary hoeing, crop rotation, preventive measures, and
herbicides are techniques that could be used in an integated approach to control weeds in
seed corn production. The use of a row cultivation following an application of a
preemergence herbicide has been shown to enhance weed control in a ﬁeld corn
production system (Mulder and Doll 1993). Seed corn producers in southwest Michigan
usually apply a preemergence herbicide and use row cultivation later in the season for
weed management. This weed management system will often provide suﬁcicnt control
of early season weeds, but control of late emerging weeds, primarily annual gasses, is
inconsistent. Seed corn producers will often apply a herbicide at the time of ﬁnal row
cultivation to control late emerging annual gasses. This method of herbicide application
is commonly referred to as a layby application.

Cover crops have been shown to reduce weed populations in many agonomic

32

production systems (Ateh and Doll 1996; Ilnicki and Enache 1992; Einhelling and
Leather 1988). The reduction of weed densities by cover crops can be attributed
primarily to physical competition between weeds and the cover crop, or by allelopathic
interactions of cover crop residues (Lal et al. 1991; Putnam et al. 1983). Mt. Pleasant and
Scott (1991) have reported weed suppression by interseeded cover crops in a ﬁeld corn
production system. This type of cover cropping system could easily be incorporated into
a seed corn production system, because the environment, which favors the infestation of
weeds, can be ideal for establishment of a cover crop.

This trial was conducted to determine the effect of interseeded cover crops on
annual gass weeds in a seed corn production system, and to determine the effect of cover
crops on seed corn yield. The effect of EPTC and metolachlor on annual ryegass and
crimson clover was evaluated in this ﬁeld trial. The effect of a layby metolachlor

application on gass weed control was also investigated in this ﬁeld trial.

MATERIALS AND METHODS
Field trials were established in seed corn production ﬁelds in St. Joseph County
Michigan in 1995 and 1996. The soil was a Spinks sandy loam (sandy mixed, mesic
Psarnmentic Hapludalfs) with a pH of 6.5 and 1.1% organic matter in 1995. In 1996, the
soil was a Spinks sandy loam (sandy mixed, mesic Psarnmentic Hapludalfs) with a pH of
6.8 and 1.6% organic matter. Dates of ﬁeld operations and experimental measurements
are found in Table 1. Primary tillage consisted of fall moldboard plowing in 1995, and

fall chisel plowing in 1996. Secondary tillage in 1995 consisted of a ﬁeld cultivation, and

33

in the spring of 1996 the plot area was disked and ﬁeld cultivated. In 1995 114 kg/ha of
fertilizer (15% N, 15% P205, 2% K20) was applied adjacent to the corn rows during
planting and 37 kg/ha of actual nitrogen was dribbled in the form of urea ammonia nitrate
at row cultivation on June 13, 1995. In 1996 91 kg/ha of fertilizer (15% N, 15% P205,
2% K20) was applied adjacent to the corn rows during planting and 39 kg/ha of actual
nitrogen was dribbled June 26, 1996. Seed corn inbreds were planted in a pattern of four
female inbreds to one male inbred in 76 em rows on May 15, 1995 and on May 18, 1996.
The entire plot area was irrigated with center pivot irrigation (Table 2). The ﬁeld was
irrigated to maintain an available water capacity geater than 60%.

The experimental design was a two factor randomized complete block with four
replications. The factors were cover crop treatments and herbicide application.
Treatments included annual ryegrass, crimson clover, a mixture of annual ryegass +
crimson clover, and no cover crop seeded over plots treated with a preemergence
application of either 4.84 kg/ha EPTC or 1.68 kg/ha of metolachlor. In 1995 and 1996,
annual ryegass was seeded at 28 kg/ha, crimson clover was seeded at 17 kg/ha, and an
annual ryegass + crimson clover mixture was seeded at 21 kg/ha + 12 kg/ha. Treatments
including annual ryegass seeded at 56 kg/ha, crimson clover seeded at 34 kg/ha and an
annual ryegass + crimson clover mixture seeded at 42 kg/ha + 24 kg/ha were added in
1996. Treatments including crimson clover were inoculated with Rhizobia species in
1996. Other treatments included a layby application of metolachlor, a weed free control,

and an untreated check. The layby application of 1.12 kg/ha metolachlor was applied

after ﬁnal row cultivation.

34

Cover crops were broadcast seeded over 20 cm tall seed corn in the V4 gowth
stage on June 12, 1995, and 46 cm tall seed corn in the V6 gowth stage on June 24,
1996. In 1995, a tractor mormted Gandy air seeder‘ was used to seed the cover crops, and
in 1996 the cover crops were seeded using a shoulder harness whirl seeder. Plots were
cultivated June 13, 1995 and June 26, 1996. Preemergence herbicides were applied with
a tractor mounted compressed air plot sprayer using 8003 ﬂat fan nozzles calibrated to
deliver 187 L/ha at a pressure of 207 kPa. Approximately 1.3 cm of irrigation was
provided shortly after herbicide applications in order to incorporate the EPTC.
Preemergence herbicides were applied on May 17, 1995 and on May 20, 1996. Layby
treatments were applied in 76 em bands using 8003B even ﬂat fan nozzles calibrated to
deliver 117 L/ha at 207 kPa. Layby treatments were applied on June 13, 1995 and June
27, 1996.

The densities of cover crop species and annual gass weeds were measured within
four 25 by 38 cm quadrats for each plot. The measurements were recorded 75 days after
seed corn planting. Fall panicum was the predominant gass weed species present in
1995, and large crabgass was the predominant species in 1996. Heights of ﬁve randomly
chosen cover crops were measured with a meterstick. Visual weed control ratings were
recorded in all treatments for gass weeds near the time of harvest in both 1995 and 1996.
The rating scale ranged from 0 (no apparent weed control) to 100% (complete weed
control). The annual ryegass cover crop was severely injured from preemergence

applications of metolachlor. Therefore, weed densities and control ratings in plots which

 

' Gandy Company; Owatonna, Minnesota 55060

35

were heated with a preemergence application of metolachlor are not reported. The seed
corn was harvested for yield determination in 1995, but not in 1996 due to a harvesting
error. A 9 m section of a middle corn row was harvested by hand and weight and
moisture were recorded. Grain yields were adjusted to a 15.5% moisture level. Cover
crop densities, cover crop heights, gass weed densities, gass weed control ratings, and
yields were analyzed using analysis of variance. The density of the gass weeds in the
unheated plots were signiﬁcantly higher in 1996 as compared to 1995, however treatment
by year interactions were not signiﬁcant. Therefore, data were combined over years.
Means were separated using the least sigriﬁcant difference procedure at the 0.10 level of
signiﬁcance for gass weed density comparisons, and at the 0.05 level of signiﬁcance for

cover crop height, cover crop density, and gass weed conhol comparisons.

RESULTS AND DISCUSSION
Cover crop injury. The height and density of interseeded annual ryegass and crimson
clover were used to quantify potential injury of the cover crops. EPTC and metolachlor
had no effect on the height or density of crimson clover. The height and density of
annual ryegass was signiﬁcantly reduced when annual ryegass was seeded into plots
previously heated with metolachlor as compared to plots previously heated with EPTC
(Table 3). Annual ryegass injury ﬁom metolachlor was severe enough to negatively
impact any possible weed suppression ﬁom the annual ryegass. Past research has
revealed potential reduction in germination and gowth of interseeded cover crops ﬁom

preemergence herbicides that are still persistent in the soil at the time of cover crop

36
seeding (Cramer 1986; Scott and Burt 1987). EPTC has a shorter soil persistence than

metolachlor (Anonymous 1994), and has been successfully used in many previous
interseeded cover crop research hials (Scott and Brut 1987; Scott et al. 1987; Stute and
Posner 1993).

Grass weed suppression from cover crops. The density of annual gass weeds, 75 days
after seed corn planting, was reduced in plots seeded with annual ryegass and the annual
ryegass + crimson clover mixture as compared to plots without a cover crop (Table 4).
The density of the gass weeds in plots seeded with crimson clover were equal to the
density of gass weeds in the plots without a cover crap. Visual differences in conhol of
the gass weeds at corn harvest (112 days after seed corn planting) were not apparent
(Table 4). Suppression of weeds in a corn production system interseeded with cover
crops has been previously reported (Mt. Pleasant and Scott 1991).

Weed suppression ﬁom an interseeded cover crop could be athibuted to factors
associated with plant competition. Aldrich (1984) described competition as being a
relationship between plants in which the supply of a gowth factor, such as water, light,
carbon dioxide, or nuhients falls below the combined demands. Most, if not all, acres of
seed corn are irrigated, therefore, the competition for water is generally low. A canopy
provided ﬁom an interseeded cover crop would compete with the late emerging gass
weeds for light, especially if the cover crop was established before weed emergence. In
1996, the seeding rates of the cover crops were doubled to determine the effect of
increased cover crop densities on gass weed suppression. Increasing the cover crop

swding rates did not sigriﬁcantly effect the density or visual conhol of the gass weeds at

37

com harvest (data not reported). The cover crops in our ﬁeld hials did not suppress gass
weeds to an acceptable level. The gowth characteristics of annual ryegass and crimson
clover in relation to the gowth characteristics of gass weeds might have conhibuted to
the lack of sufﬁcient gass weed conhol. Annual ryegass and crimson clover are cool
season plants (Sarrantonio 1994), while fall panicum and large crabgass are warm season
gasses (Stubbendieck 1994). If fall panicum or large crabgass germinate near the time
cover crops are seeded, the rapid gowth of the gass weeds would probably eliminate any
potential competition for light that a cover crop might provide. A warm season cover
crop species that could be established before weeds emerge, and not compete with corn
for water might be a more suitable interseeded cover crop for seed corn production.
Layby applications of metolachlor. The addition of a layby application of metolachlor
increased gass control as compared to plots without a layby h'eahnent (Table 5). This
occurred where either metolachlor or EPTC was applied at planting. The layby
h'eahnents provided geater than 85% control of the gass weeds throughout the entire
gowing season. Previous research has shown that layby herbicide applications generally
provided season long conhol of weeds and reduced weed seed production (Moomaw et
al. 1983; Moomaw and Marten 1984).

Seed corn yields. In 1995, differences in seed corn yields were not apparent between
cover crops which were seeded into plots heated with EPTC (Table 6). Seed corn yields
were reduced in plots that were seeded with the annual ryegass + crimson mixture and
heated with a preemergence application of metolachlor. Interseeded cover crops have

been established in ﬁeld corn without reducing corn yield (Helsel et al. 1991; Eadie et al.

38
1 992).

Cover crops were successfully established following a prior application of EPTC.
However, a preemergence application of metolachlor severely injured the annual ryegass
cover crop. Treahnents containing annual ryegass reduced the density of gass weeds at
midseason. However, the reduction in gass weed densities did not result in increased
gass conhol at seed corn harvest. Although seed corn production is well suited for

interseeded cover crops, substantial suppression of weeds was not observed in this study.

39
LITERATURE CITED

Aldrich, R J. 1984. Weed crop ecology: principles of weed management. Breton
Publishers, North Scituate, MA.

Anonymous. 1994. WSSA Herbicide Handbook 7'“ ed. Weed Sci. Soc. Of America.
Champaign, IL. 352p.

Ateh, C. M. and J. D. Doll. 1996. Spring planted winter rye (Secale cereale) as a living
mulch to conhol weeds in soybean (Glycine max). Weed Tech. 10:347-353.

Cramer, C. 1986. Herbicides and overseeding can mix. The New Farm. May/June.
8:24-25.

Eadie, A. G., C. J. Swanton, J. E. Shaw, and G. W. Anderson. 1992. Integation of
cereal cover crops in ridge-tillage corn production. Weed Tech. 6:533-560.

Einhellig, F. A. and G. R. Leather. 1988. Potentials for exploiting allelopathy to enhance
crop production. J. of Chem. Ecology. 14:1829-1844.

Harvey, R. G. and G. R. McNevin. 1990. Combining cultural practices and herbicides to
conhol wild-proso millet (Panicum miliaceum). Weed Tech. 4:433-439.

Harvey, R. G. 1994. Managing weed populations. Proc. 49th Annual Corn and Sorghum
Res. Conf. 49:15-26.

Helsel, Z. R, N. C. Wollenhaupt, and K. D. Kephart. 1991. Cover crop management for
soybean production in northern Missouri. p. 149-151. In W. L. Hargove (ed.) Cover
crops for clean water. Soil and Water Conserv. Soc., Ankeny, IA.

Ilnicki, R. D. and A. J. Enache. 1992. Subterranean clover living mulch: an alternative
method of weed conhol. Agic., Ecosystems, and Environ. 40:249-264.

Knake, E. L., and F. W. Slife. 1965. Giant foxtail seeded at various times in corn and
soybeans. Weeds. 13:331-334.

Lal, R, E. Regnier, D. S. Eckert, W. M. Edwards, and R Hammond. 1991. Expectations
of cover crops for sustainable agriculture. p. 1-11. In W. L. Hargove (ed.) Cover crops
for clean water. Soil and Water Conserv. Soc., Ankeny, IA.

Moomaw, R. S., and A. R Martin. 1984. Cultural practices affecting season-long weed
conhol in irrigated corn (Zea mays). Weed Sci. 32:460-467.

40

Moomaw, R S., A. R Martin, and R G. Wilson, JR 1983. Layby herbicide
applications for season-long weed control in irrigated corn (Zea mays). Weed Sci.
3 1 : 137-140.

Mt. Pleasant, J., and T. W. Scott. 1991. Weed management in corn polycultm'e systems.
p.151-152. In W. L. Hargove (ed.) Cover crops for clean water. Soil and Water
Conserv. Soc., Ankeny, IA.

Mulder, T. A. and J. D. Doll. 1993. Integating reduced herbicide use with mechanical
weeding in corn. Weed Tech. 7 :382-389.

Putnam, A. R, J. Deﬁank, and J. P. Barnes. 1983. Exploitation of allelopathy for weed
control in annual and perennial cropping systems. J. of Chem. Ecology. 9: 1001-1009.

Sanantonio, M. 1994. Northeast cover crop handbook. Rodale Institute. Emmanus PA.
1 18 p.

Scott, T. W. and R F. Burt. 1987. Use of red clover in corn polyculture systems. p.

101-103. In J.R Powers (ed.) The role of legumes in conservation tillage systems. Soil
Conserv. Soc. Am., Ankeny, IA.

Scott, T. W., J. Mt. Pleasant, R. F. Burt, and D. J. Otis. 1987. Conhibutions of gound
cover, dry matter, and nihogen from intercrops and cover crops in a corn polyculture
system. Agon. J. 79:792-798.

Stubbendieck, J., G. Y. Friisoe, M. R. Bolick. 1994. Weeds of Nebraska and the geat
plains. NE Dept. of Agic. Lincoln, NE. 589 p.

Stute, J. K. and J. L. Posner. 1993. Legume cover crop options for gain rotations in
Wisconson. Agon. J. 85:1128-1132.

41

Table 1. Dates of ﬁeld operations and experimental measm'cments.

 

 

1995 1996
Seed corn planting May 16 May 18
Application of preemergence herbicides May 17 May 20
Cover crop seeding June 12 June 24
Final cultivation June 13 June 26
Application of layby metolachlor June 13 June 27
Grass weed densities / cover crop heights and July 31 August 2
densities
Grass conhol ratings September 7 September 6
Seed corn harvest September 7 September 18

 

42

Table 2. Rainfall and irrigation amounts during an 11 week period of the 1995 and 1996
gowing season.

 

 

 

 

 

 

 

 

Weeks after 1995 1996
cover crop
seeding Irrigation Rainfall Irrigation Rainfall

-1 0 0.76 0 4.57
0 0 0 1.52 0
l 3.81 0 2.54 0
2 O 3.68 5.08 0.76
3 1.91 0.76 2.54 0.76
4 3.18 2.54 0 0
5 1.27 4.57 0 2.29
6 O 1.32 2.54 0.25
7 0 5.33 5.08 0.64
8 1.78 0 O 1.91
9 0 4.57 0 0

total 11.95 23.53 19.30 11.18

 

43

Table 3. Eﬁ‘ect of preemergence herbicides on cover crop density and height 75 days after
seed corn planting, 1995 and 1996.

 

 

 

 

Annual ryegass Crimson clover
Density Height Density Height
plants/m2 cm plants/m2 cm
Metolachlor 221 b‘ 14 b 174 a 13 a
EPTC 358 a 20 a 149 a 15 a

 

'Numbers followed by the same letter within columns are not signiﬁcantly
different according to Fisher’s Protected LSD Test at a = 0.05

44

Table 4. Eﬂ‘ect of cover crops on gass weed density 75 days after seed corn planting and
gass weed conhol 112 days after seed corn planting, 1995 and 1996.

 

 

 

Grass weeds
Tm”? Density Conhol
75 DAP 112 DAP
plants/m2 % of unheated
Annual Ryegass 19 b" 66 a°
Crimson Clover 32 a 64 a
Annual Ryegass + 12 b 64 a
Crimson Clover mixture
No cover crop 31 a 65 a

 

‘All plots were heated with EPT C prior to seed corn planting
”Numbers followed by the same letter within this column are not signiﬁcant
according to Fisher’s Protected LSD Test at a = 0.10

“Numbers followed by the same letter within these columns are not signiﬁcant
according to Fisher’s Protected LSD Test at a = 0.05

 

45

Table 5. Eﬂ'ect of layby metolachlor applications on grass conhol 112 days after seed
corn planting, 1995 and 1996.

 

 

 

 

Metolachlorl EPTC”
Controlc
------- % of unheated -------
Layby 88 a 86 a
No layby 77 b 65 b

 

”Treated with a preemergence application of metolachlor

”Treated with a preemergence application of EPTC

cNumbers followed by the same letter within columns are not signiﬁcant
according to Fisher’s Protected LSD Test at a = 0.05

46

Table 6. Eﬁ‘ect of cover crops on seed corn yield, 1995.

 

Metolachlor' EPTC”
Tm“ Yield
----1000 kg/ha----

Annual Ryegass 4.5 abc 3.8 a
Crimson Clover 4.4 ab 4.2 a
Annual Ryegass + Crimson 3.7 b 3.6 a
Clover mixture

No cover crop 5.1 a 3.5 a

 

'Treated with a preemergence application of metolachlor

bTreated with a preemergence application of EPTC

cNumbers followed by the same letter within columns are not signiﬁcant
according to Fisher’s Protected LSD Test at a = 0.05

CHAPTER3

Potential Use of Corn Herbicides in Annual Ryegrass and Crimson Clover Cover

Cropping Systems

Abstract. Greenhouse hials were conducted to determine the effect of preemergence and
postemergence herbicides on annual ryegass, oat, crimson clover, and medium red
clover. EPTC, ﬂumctsulam + metolachlor, metolachlor, and pendimethalin were tested
and each injured annual ryegass. EPTC, ﬂumetsulam + metolachlor, and metolachlor
also injured oat. Crimson clover and medium red clover were signiﬁcantly injured ﬁ'om
ﬂumetsulam + metolachlor and metolachlor. The eﬁ’ect of EPTC and pendimethalin on
both clover species was variable. Primisulfuron and nicosulfuron severely injured the
annual ryegass and cat. Response of both gass species to bromoxynil and 2,4-D amine
was variable. Bentazon did not injure either of the gass species. All of the
postemergence herbicides injured the crimson clover and medium red clover. Field hails
were conducted in 1995 and 1996 to determine the required time interval between an
application of a preemergence herbicide and seeding of annual ryegass and crimson
clover to avoid herbicide injury. Annual ryegass was not successfully established after
an application of metolachlor. Establishment of annual ryegass at an interval of time
following EPTC was successful. Annual ryegass seeded after pendimethalin was not
successfully established in 1995, but was successfully established in 1996. Crimson

clover was injured when seeded the same day the herbicides were applied. Crimson

47

48

clover was successfully established when seeded at an interval of time following
application of pendimethalin, EPTC or metolachlor. In all cases, successful
establishment of the cover crop was dependent on the time interval between herbicide
application and cover crop seeding.

Nomenclature: bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-
dioxide; bromoxynil, 3,5-dibromo-4-hydroxybenzonihile; dicamba, 3,6-dichloro-2-
methoxybenzoic acid; EPTC, S-ethly dipropyl carbamothioate; metolachlor, 2-chloro-N-
(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; nicosulfuron, 2-
[[[[(4,6-dimethoxy-2-pyrimidynil) amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-
pyridinecarboxamide; pendimethalin, N-(l -ethylpropyl)-3,4-dimethyl-2,6-
dinihobenzenamine; primisulﬁrron, 2-[[[[[4,6-bis(diﬂouromethoxy)-2-
pyrimidinyl]amino]carbonyl]amino]sulfonyl] benzoic acid; 2,4-D (2,4-
dichlorophenoxy)acetic acid; annual ryegass, Lalium mulnﬂorum; crimson clover

T rtfolium incarnatum L. # TRFIN; oat, Avena sativa L. # AVESA; red clover, T rifolium
pratense L. # TRFPR.

Additional index words: bentazon, bromoxynil, dicamba, EPTC, metolachlor,

nicosulfuron, primisulfuron, 2,4-D amine, cover crops, interseeded, overseeded

49

INTRODUCTION

Cover cropping systems offer many potential beneﬁts to agriculture (Lal et al.
1991; Bug 1991; Frye et al. 1983). One type ofsuccessful cover cropping system
includes the use of interseeded cover crops. In an interseeded cover cropping system a
cover crop is seeded directly into a gowing row crop. Intemeeded cover crops provide
gound cover and have been shown to yield as much forage as cover crops gown outside
of a row crop (Stute and Posner 1993; Scott and Brut 1987). A popular establishment
time for interseeded cover crops is at ﬁnal row cultivation, and past research has revealed
no apparent reductions in row crop yields when cover crops were seeded near this time
(Scott et al. 1987; Helsel et al. 1991; Eadie et al. 1992). According to Exner and Cruse
(1993), interseeded cover crops should be established in an environment with low weed
populations.

In row crop production, herbicides and tillage are often used to reduce weed
populations. Many of the herbicides used in row crop production can be harmful to an
interseeded cover crop, and application of these herbicides will often determine the time
an interseeded cover crop can be seeded (Olson et al. 1986; Scott and Burt 1987; Cramer
1986). Scott and Burt (1987) investigated the establishment of interseeded red clover
following an application of EPTC, which is a herbicide with short soil persistence
(Anonymous 1994). The herbicide heahnents in their hials did not injure the interseeded
red clover. Many of the ﬁeld research hials investigating interseeded cover crops have
used EPTC, or a combination of EPTC and other banded herbicides (Olson et al. 1986;

Scott et a1. 1987; Stute and Posner 1993). In 1987, Cramer published a list of empirical

50

involving herbicide use in cover crops has focused primarily on using the herbicides for
cover crop suppression (Hartwig and Hoffman 1975; White and Worsham 1990; Grimn
and Dabney 1990). Little information exists on using herbicides to conhol weeds in a
living cover crop, and the eﬂ‘ect of the herbicides on the cover crop. Likewise, the effect
of previously applied herbicides on cover crop establishment and gowth is not well
understood. Such information is needed in order to gain the most beneﬁts ﬁom an
interseeded cover cropping system.

The objectives of our research were to investigate the effect of corn herbicides on
cover crops gown in geenhouse conditions, and to determine the required time interval
between an application of a preemergence herbicide and seeding of annual ryegass or

crimson clover to avoid herbicide injury.

MATERIALS AND METHODS
Greenhouse Trials. Studies were conducted in the geenhouse to determine the effect of
preemergence and postemergence herbicides on cover crop species. Environmental
conditions were maintained at 27°C i 5 °C with a 16 hour photoperiod of natural lighting
supplemented with metal halide lighting giving a midday photosynthetic ﬂux of
700uE/m2/s. All herbicides were applied with a continuous link belt sprayer equipped
with an 8001B ﬂat fan nozzle calibrated to deliver 234 L/ha of solution at a pressure of
221 kPa.

The cover crops for the postemergence herbicide hial were seeded into 945 ml

5 1
plastic pots ﬁlled with Bacctol professional potting mix and were watered as needed.
Plants were thinned to four annual ryegass, three oat, four crimson clover, and four
medium red clover plants per pot prior to herbicide application. Bentazon (1.12 kg/ha),
bromoxynil (0.42 kg/ha), dicamba (0.56 kg/ha), nicosulfuron (0.035 kg/ha), primisulfuron
(0.040 kg/ha), and 2,4-D amine (0.56 kg/ha) were applied to 10 cm annual ryegass, 18
cm cat, 5 cm crimson clover, and 5 cm medium red clover. Liquid urea ammonium
nihate (28% nihogen) at 4% v/v and non-ionic surfactant at 0.25% v/v were added to
primisulfuron and nicosulfuron, while crop oil concenhate at 1% v/v was added to
bentazon. Plant heights were measured 14 days after herbicide application and the
abovegound portion of the plants were harvested. The harvested shoots were dried in a
38°C oven for at least three days at which time dry weights were measured.

In the preemergence geenhouse hial, ten seeds of each cover crop species were
seeded into 945 ml pots ﬁlled with a Spinks loamy sand soil (sandy, mixed, mesic
Psarnmentic Hapludalfs) with 1.0% organic matter and a pH of 6.5. The seeded pots
were subsequently heated with 2.35 kg/ha ﬂumetsulam + metolachlor, 2.24 kg/ha
metolachlor, and 1.68 kg/ha pendimethalin. Cover crops were also seeded into pots
previously heated with 4.48 kg/ha EPTC. EPTC was applied to 470 m1 of soil and
incorporated by thoroughly mixing the heated soil in a plastic bag. The number and
height of emerged plants were measured 28 days after herbicide application and the
abovegound portion of the plants were harvested. The harvested shoots were dried in a

38°C oven for at least three days at which time dry weights were measured.

 

IBaccto is a product of Michigan Peat Co. Houston, TX 77098

52

The preemergence and postemergence hials were repeated in time and were
designed as a randomized complete block with six replications for the preemergence
herbicide hial and four replications for the postemergence herbicide hial. Data were
analyzed using analysis of variance, and means were separated using Fisher’s protected
least signiﬁcant difference test at the 0.05 level of signiﬁcance. Treahncnt by run
interactions were signiﬁcant, therefore the data for each run are reported separately.
Field Trials. A ﬁeld hial seeded with annual ryegass and a ﬁeld hial seeded with
crimson clover were each established at the Michigan State University Agonomy
Research Farm at East Lansing in 1995 and 1996. The soil was a Capac loam (ﬁne-
loamy, mixed, mesic Aerie Ochraqualfs) with 2.6% organic matter and a pH of 6.5 in
1995, and 2.5% organic matter and a pH of 6.4 in 1996. The site was chisel plowed in
the fall of 1994, and moldboard plowed in the fall of 1995. Secondary tillage consisted
of spring disking and ﬁeld cultivation. In 1995, 140 kg/ha of fertilizer (6% N, 24%P205,
24%K20) was broadcast prior to ﬁeld cultivation, while 336 kg/ha of fertilizer (6% N,
24%P205, 24%KZO) was broadcast in 1996. All herbicides were applied with a haetor
mounted compressed air plot sprayer using 8003 ﬂat fan nozzles calibrated to deliver 187
um at a pressure of 207 kPa. Precipitation data ﬁom the research hials are listed in
Table 1.

The ﬁeld hials were designed in a split block arrangement with four replications.
Both hials were arranged in a similar fashion with the ships of cover crop seeded
perpendicular to the ships of herbicide application. On May 18, 1995 and May 7, 1996

metolachlor at 1.68 kg/ha, pendimethalin at 1.68 kg/ha, and EPTC at 4.48 kg/ha were

53

applied. The EPTC was incorporated using a ﬁeld cultivator. Annual ryegass was
seededat28 kg/haandcrimsoncloverwas seededat 17 kg/hausingagaindrill, andthe
ships were cultipacked. Seeding dates corresponded to the gowth stage of corn that was
gown adjacent to the plots. The seeding dates are reported in Table 2. Five foot buffer
ships were used between each ship of herbicide application in order to compensate for
potential dragging of heated soil during seedbed preparation.

Cover crop densities, heights, and visual injury were measured 30 days after the
cover crops were seeded. Plants in two one meter sections of row, and heights of ﬁve
randomly chosen cover crop plants were recorded. Visual injury ratings ranged hour 0 to
100%, with 0 representing no injury and 100% indicating complete death of the plant.
All data were analyzed using analysis of variance, and means were separated using
Fisher’s protected least sigriﬁcant difference test at the 0.05 level of sigriﬁcance.
Treahncnt by year interactions were signiﬁcant, therefore data are reported separately for

each year.

RESULTS AND DISCUSSION
Greenhouse preemergence herbicide hials. EPTC, ﬂumetsulam + metolachlor, and
metolachlor severely injured annual ryegass (Table 3). In the ﬁrst run of the experiment
no annual ryegass plants emerged following an application of these herbicides, and only
a small number of annual ryegass plants emerged in the second run of the experiment.
The emergence of annual ryegass after an application of pendimethalin was reduced in

the ﬁrst run of the experiment but was not reduced in the second run. However, the dry

54

weight of the plants that did emerge was reduced at least 30% to that of the unheated
plants. Based on the results of this hial, annual ryegass appears to be sensitive to EPTC,
ﬂumetsulam + metolachlor, metolachlor, and pendimethalin

Practically no oat plants emerged following an application of EPTC (Table 3).
The emergence and dry weight of oat plants following an application of flumetsulam +
metolachlor and metolachlor was signiﬁcantly reduced as compared to the unheated oat
plants. Pendimethalin had no signiﬁcant eﬁ‘eet on the gowth or emergence of oat plants.
The results ﬁorn this hial would suggest that cat is sensitive to EPTC, ﬂumetsulam +
metolachlor, and metolachlor, but is tolerant of pendimethalin.

The emergence and dry weight of crimson clover following an application of
ﬂumctsulam + metolachlor were signiﬁcantly reduced in both rims of the experiment
(Table 4). Metolachlor reduced the emergence and dry weight of crimson clover in the
ﬁrst run of the experiment. When the experiment was repeated, the emergence was not
reduced but the dry weight was reduced. EPTC did not reduce the emergence of crimson
clover in either run of the experiment. However, the dry weight of crimson clover was
reduced 47% in the second run. The emergence and dry weight of crimson clover was
not signiﬁcantly reduced ﬁom an application of pendimethalin. Crimson clover appears
to be most sensitive to ﬂumetsulam + metolachlor and metolachlor. Injury to crimson
clover from EPTC could be expected based on the results of this hial. Data would
suggest some tolerance of crimson clover to pendimethalin.

Application of ﬂumetsulam + metolachlor and metolachlor severely reduced the

emergence and dry weight of medium red clover (Table 4). Pendimethalin reduced the

55

emergence and dry weight of medium red clover in the ﬁrst run of the experiment.
However, the dry weight and emergence were not aﬁ'ected in the second run of the
experiment. EPTC did not reduce the emergence or dry weight of medium red clover in
either run of the experiment. Medium red clover was sensitive to ﬂumetsulam +
metolachlor and metolachlor, but was very tolerant of EPTC.
Greenhouse postemergence herbicide trial. Applications of nicosulfuron and
primisulfuron severely reduced the dry weight and height of annual ryegass (Table 5).
The height of annual ryegass was not reduced when heated with dicamba. However, the
dry weight of the plants in the second run of the experiment was reduced. Bromoxynil
reduced the dry weight but not the height of annual ryegass. Bentazon and 2,4-D amine
did not affect the dry weight and height of annual ryegass. Data from this hial would
suggest that annual ryegass is very sensitive to nicosulfuron and primisulfuron, and
tolerant of bentazon and 2,4-D amine. Injury to annual ryegass is possible from
applications of dicamba or bromoxynil.

Primisulfuron and nicosulfuron severely reduced the height and dry weight of oat
(Table 5). Bromoxynil, dicamba, and 2,4-D amine did not reduce the dry weight and
height of cat in the ﬁrst run of the experiment. However, a small reduction in cat dry
weight from these herbicides was apparent in the second run. The height and dry weight
of oat were not affected by bentazon. The results ﬁom this hial suggest oat plants are
quite sensitive to nicosulfuron and primisulfuron. Oat appeared to have fair tolerance to
applications of bentazon, bromoxynil, dicamba, and 2,4-D amine.

All of the herbicides reduced the dry weight of crimson clover (Table 6).

56

However the height of crimson clover was not reduced ﬁom bentazon in the ﬁrst run of
the experiment, and 2,4-D amine in the second run of the experiment. Crimson clover
appears to be sensitive to all of the herbicides tested in this hial.

The dry weight of medium red clover was reduced ﬁom all of the herbicides
tested, except for 2,4-D amine in the second run of the experiment (Table 6). The height
of medium red clover was not reduced ﬁom bentazon or 2,4-D amine in either runs of the
experiment. The results of this hial suggest partial tolerance of medium red clover to
bentazon and 2,4-D amine, and practically no tolerance to the rest of the herbicides tested.
Field trials. Previously reported geenhouse hials have revealed potential annual
ryegass and crimson clover injury from EPTC, metolachlor, and pendimethalin (Tables
3 and 4). EPTC, pendimethalin, and metolachlor were chosen for these ﬁeld hials based
on the relative persistence of the herbicides in the soil. Metolachlor has been reported to
have the longest soil half life of the three herbicides, and EPTC has the shortest
(Anonymous 1994). These herbicides are generally applied to the soil before emergence
of a row crop.

Annual ryegrass field trials. Annual ryegass was severely injured from metolachlor
regardless of seeding time in 1995 and 1996, and the visual injury was often geater than
90% (Table 7). Annual ryegass density was signiﬁcantly reduced ﬁom pendimethalin at
all seeding times in 1995. However, annual ryegass height and density were not reduced
from pendimethalin when it was seeded at the fourth timing in 1996. The height and
density of annual ryegass, seeded at the fourth timing in 1995 and the third timing in

1996, were not reduced ﬁorn EPTC.

57

Based on the results of these hials, establishment of annual ryegass following an
application of EPTC has little risk provided the ryegass is seeded at least 40 days
following application. Establishing annual ryegass following an application of
pendimethalin would involve more risk based on the observed injury in this hial.

Results hour this ﬁeld hial suggest annual ryegass should not be seeded up to seven
weeks following an application of metolachlor to mrnimize risk of herbicide injury.
Crimson clover ﬁeld trials. Crimson clover was signiﬁcantly injured and the height was
reduced when it was seeded the same day EPTC, metolachlor, and pendimethalin were
applied (Table 3). However, crimson clover density was not reduced at this seeding time.
The density and height of crimson clover were not reduced ﬁom pendimethalin when the
clover was seeded at the second timing in both years. Crimson clover injury was less
than 20% and plant density was not reduced when the clover was seeded at the third
timing following application of EPTC and metolachlor in 1995 and 1996.

Susceptibility of a cover crop to a herbicide and the soil persistence of the
herbicide are important factors in the risk of herbicide injury to interseeded cover crops.
Crimson clover establishment was possible provided that the crimson clover was seeded
at some time interval following application of the herbicides tested. The results ﬁom this
hial indicate crimson clover could be established sooner following an application of

pendimethalin than metolachlor or EPTC.

58
LITERATURE CITED

Anonymous. 1994. WSSA Herbicide Handbook 7"I ed. Weed Sci. Soc. Of America.
Champaign, IL. 352p.

Bugg, R. L. 1991. Cover crops and conhol of arthropod pests of agriculture. In W. L.
Hargove (ed). Cover crops for clean water. Ankeney, IA p. 157-163.

Cramer, C. 1986. Herbicides and overseeding can mix. The New Farm. May/June.
8:24-25.

Eadie, A. G., C. J. Swanton, J. E. Shaw, and G. W. Anderson. 1992. Integation of
cereal cover crops in ridge-tillage corn production. Weed Tech. 6:533-560.

Exner, D. N. and R M. Cruse. 1993. Interseeded forage legume potential as winter
gound cover, nihogen source, and competition. J. Prod. Agri. 6:226-231.

Frye, W. W., J. H. Herbek, and R. L. Blevins. 1983. Legume cover crops in production
of no-tillagc corn. p. 179-191. In W. Lockeretz. (ed.) environmentally sound agriculture.
Praeger Publishers, NY.

Grifﬁn, J. L. and S. M. Dabney. 1990. Preplant - postemergence herbicides for legume
cover-crop conhol in minimum tillage systems. Weed Tech. 4:332-336.

Hartwig, N. L. and L. D. Hoffman. 1975. Suppression of perennial legume and gass
cover crops for no-tillage corn. Proc. N. E. Weed Sci. Soc. 29:82-88.

Helsel, Z. R, N. C. Wollenhaupt, and K. D. Kephart. 1991. Cover crop management for
soybean production in northern Missouri. p. 149-151. In W. L. Hargove (ed.) Cover
crops for clean water. Soil and Water Conserv. Soc., Ankeny, IA.

Lal, R, E. Regrier, D. S. Eckert, W. M. Edwards, and R. Hammond. 1991. Expectations
of cover crops for sustainable agiculture. p. 1-11. In W. L. Hargove (ed.) Cover crops
for clean water. Soil and Water Conserv. Soc., Ankeny, IA.

Olson, R. A., W. R. Raun, Y. S. Chun, and J. Skopp. 1986. Nihogen management and
interseeding effects on irrigated corn and sorghum and on soil shength. Agon. J. 78:
856-862.

Scott, T. W. and R. F. Burt. 1987. Use of red clover in corn polyculture systems. p.
101-103. In J .R. Powers (ed.) The role of legumes in conservation tillage systems. Soil
Conserv. Soc. Am., Ankeny, IA.

 

59

Scott, T. W., J. Mt. Pleasant, R F. Burt, and D. J. Otis. 1987. Conhibutions of gound
cover, dry matter, and nihogen ﬁom intercrops and cover crops in a corn polyculture
system. Agon. J. 79:792-798.

Stute, J. K. and J. L. Posner. 1993. Legume cover crop options for gain rotations in
Wisconsin. Agon. J. 85:1128-1132.

White, R. H. and A. D. Worsham. 1990. Conhol of legume cover crops in no-till corn
(Zea mays) and cotton (Gossypium hirsutum). Weed Tech. 4:57-62.

60

Table I. Rainfall amounts during a 13 week period of the 1995 and 1996 gowing
season.

 

 

 

 

 

 

wﬁﬁ: mini?“ 1995 1996
cm

-1 0.25 0.23
0 2.29 2.77
1 3.00 4.93
2 0.36 0.38
3 0.53 0.69
4 0 2.92
5 2.67 0.28
6 4.39 10.16
7 0.46 0
8 3.15 0
9 2.62 0.56
10 0.36 0.20
11 4.11 0.08

 

 

 

total 24.19 23.20

 

 

 

 

 

61
Table 2. Cover crop seeding dates.
Corn Growth 1995 1996
Stage‘ Date DAT” Date DATb

Timing 1 at planting May 18 0 May 7 0
Timing 2 Vl-V2 June 2 15 May 24 17
Timing 3 V3-V4 June 14 28 June 11 35
Timing 4 V5-V6 June 26 40 June 25 49

 

‘Growth stages of corn gown adjacent to the cover crop
l’DAT = Days after application of preemergence herbicides

‘4’ waver. ‘H‘n- 'mq
I

 

62

Table 3. Effect of preemergence herbicides on gass cover crop species 28 days after
heahnent.

 

Annual Ryegass Oat
Dry Weight Emergence Dry Weight Emergence

 

 

 

% reduction no. of plants % reduction no. of plants

 

 

 

 

First nm

EPTC 100 O 100 0
ﬂumetsulam + 100 0 39.1 4.5
metolachlor

metolachlor 100 0 54.8 4.5
pendimethalin 30.7 5.7 0 9.3
unheated 0 7.2 0 9.7
LSD (0.05) 18.6 1.1 25.9 1.5

Second nm

EPTC 100 0.5 100 0.2
ﬂumetsulam + 100 0.3 40.3 5.5
metolachlor

metolachlor 100 0.5 41.6 7.3
pendimethalin 36.5 6.3 7.9 9.7
unheated 0 6.8 0 8.7

LSD (0.05) 17.5 1.1 14.5 1.1

 

63

Table 4. Effect of preemergence herbicides on legume cover crop species 28 days after
heahnent.

 

Crimson Clover Medium Red Clover
Dry Weight Emergence Dry Weight Emergence

 

 

 

% reduction no. of plants % reduction no. of plants

 

 

 

 

First run

EPTC 18.9 7.8 0 6.7
ﬂumetsulam + 60.2 1.0 100 0
metolachlor

metolachlor 53.7 4.5 74.6 1 .7
pendimethalin 23.6 7.2 30.3 5.7
unheated O 7.8 0 8.5
LSD (0.05) 31.1 2.0 38.5 2.0

Second run

EPTC 47.1 7.5 0 3.3
ﬂumetsulam + 62.6 0.8 100 0
metolachlor

metolachlor 35 .4 4.8 76.5 1 .8
pendimethalin 6.5 7.7 0 4.7
unheated 0 5.2 0 5.5

LSD (0.05) 34.6 2.1 52.3 2.3

 

64

Table 5. Effect of postemergence herbicides on gass cover crop species 14 days after
heahnent.

 

 

 

 

 

 

 

 

 

Annual Ryegass Oat
Dry Weight Height Dry Weight Height
% reduction cm % reduction cm
First run r
bentazon‘ 0 9.0 3.1 25.8
bromoxynil 28.2 10.5 0 28.3
dicamba 3.9 9.3 0 27.8 ‘5.
nicosulfuron” 91.3 3.8 85.6 9.0 '
primisulfuron" 92.2 4.0 84.5 8.8
2,4-D amine 0 10.0 0 23.8
unheated 0 9.0 0 24.5
LSD (0.05) 8.4 2.2 9.7 6.8
Second run
bentazon“ 13.2 1 1.0 8.0 30.3
bromoxynil 42.1 12.8 15.9 30.3
dicamba 26.3 11.0 14.8 33.3
nicosulfuronb 94.7 6.3 75.0 20.0
primisulfuron" 76.3 9.3 77.3 17.8
2,4-D amine 18.4 15.8 10.2 30.8
unheated O 13.8 0 31.3
LSD (0.05) 22.3 4.0 8.2 3.2

 

‘included 1% v/v crop oil concenhate
bincluded 4% WV 28% urea ammonium nihate and 0.25% non-ionic surfactant

65

Table 6. Effect of postemergence herbicides on legume cover crop species 14 days after
treatment.

 

 

 

 

 

 

 

 

Crimson Clover Medium Red Clover
Dry Weight Height Dry Weight Height
% reduction cm % reduction cm
First run
bentazona 32.1 8.0 23.6 11.6
bromoxynil 88.9 0.9 92.7 1.5
dicamba 77.8 0.6 89.1 1.0
nicosulfuronb 80 2.3
primisulfuron" 81.5 1.1 89.1 1.6
2,4-D amine 30.9 6.8 36.4 11.8
unheated 0 8.9 0 11.4
LSD (0.05) 16.6 1.0 12.6 1.0
Second run
bentazon“ 60.0 6.8 20.8 1 1.0
bromoxynil 89.3 1.6 89.6 1.8
dicamba 77.3 1.5 79.2 2.8
nicosulfuron" 83.3 2.5
primisulfuronb 77.3 3.0 85.4 3.0
2,4-D amine 17.3 8.0 16.7 12.5
unheated 0 8.0 0 12.0
LSD (0.05) 15.3 1.1 17.0 1.3

 

 

‘ineluded 1% v/v crop oil concenhate
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