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Competitiveness of Giant Foxtail (Setaria faberi) and
Fall Panicum (Panicum dichotomiflorum)

 

presented by

Jason C. Fausey

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COMPETITIVENESS 0F GIANT FOXTAIL (Setariafaberi)
AND FALL PANICUM (Panicum dich otomrflorum)

By

Jason C. Fausey

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

1996

ABSTRACT

COMPETITIVENESS 0F GIANT FOXTAIL (Setariafaberi)
AND FALL PANICUM (Panicum dich otomiflorum)

By

Jason C. Fausey

Studies were conducted in 1994 and 1995 to examine giant foxtail interference in
corn. Corn yields were reduced 13% in 1994 and 14% in 1995 from 10 giant foxtail plants
per m of row. Com dry matter at maturity was decreased 24 and 23% from 10 giant foxtail
plants per 111 of row in 1994 and 1995, respectively. Ten giant foxtail plants per m of row
produced 15700 seeds per m2.

Giant foxtail seed dormancy was overcome by an accelerated after ripening treatment
of 3 days at 50 C. Fall panicum seed dormancy was overcome by a dark imbibition at 35 C
for 7 days. Giant foxtail seed germination exceeded 60% when exposed to either a constant
or alternating temperature. Fall panicum seed germination was less than 3% when exposed
to a constant temperature, but was greater than 94% when exposed to an alternating
temperature regime. Maximum emergence for giant foxtail and fall panicum was from seeds
buried 1 cm and l to 2.5 cm, respectively. The seedling growth rate of giant foxtail was six

times greater than that of fall panicum at equal temperatures.

ACKNOWLEDGMENTS

I would like to thank my graduate committee, Dr. James Kells, Dr. Karen Renner, and
Dr. Scott Swinton for all of their time and guidance into this research. I would like to thank
my co-advisers J'nn Kells and Karen Renner for their ideas and thoughts, and most importantly
their patients throughout this project.

I would like to thank Andy Chomas for the advice (asked for or not) and guidance in
making this project as smooth as possible. Ofiicemates and fiiends Corey Ransom, Bart
Tharp, Ernie Spandle, Kelly Nelson, Joe Simmons, Paul Knoerr, Bob Starke, Jefl‘ Stachler,
Julie Lich, Karen Novosel, and Gary Powell for their time and foxtail thinning skills. A
special thanks goes out to James Mickelson, who to this day has still never gotten upset with
me, for simply being Mick.

A heartwarming thanks to my parent and family for their support and encouragement
to pursue my goals. Finally, I would like to thank Lisa Ruse for the loving support

throughout the years.

iii

TABLE OF CONTENTS

PAGE

LIST OF TABLES .................................................. vi

LIST OF FIGURES ................................................. viii
CHAPTER 1. REVIEW OF LITERATURE

Introduction .................................................... 1

Giant F oxtail ................................................... 2

History and Distribution ..................................... 2

Morphology .............................................. 3

Growth and Development .................................... 3

Habitat .................................................. 7

Fall Panicum ................................................... 7

History and Distribution ..................................... 7

Morphology .............................................. 8

Growth and Development .................................... 8

Weed Interference Principles ....................................... 9

Weed Ecology ............................................ 9

Weed Interactions ......................................... 10

Allelop athy .............................................. 1 1

Competition ............................................. 12

Light and Shade Stress ..................................... 12

Water Stress ............................................. 13

Nutrient Stress ........................................... 14

C02 Stress .............................................. 15

Interference Research ............................................ 15

Weed Interference .............................................. 18

Broadleaf Weeds ......................................... 18

Grass Weeds ............................................ 20

Giant Foxtail ....................................... 21

Fall Panicum ....................................... 23

iv

TABLE OF CONTENTS (cont.)

Seed Longevity ................................................ 24
Tillage ................................................. 24
Predation ............................................... 26
Seedbanks .............................................. 27

Literature Cited ................................................ 29

CHAPTER 2. GIANT F OXTAE (Setaria faberi Herrm.) INTERFERENCE IN

NON-IRRIGATED CORN
Abstract ...................................................... 41
Introduction ................................................... 43
Materials and Methods ........................................... 46
Field Experiment ......................................... 46
Seed Study .............................................. 47
Data Analysis ............................................ 48
Results and Discussion ........................................... 49
Corn Yield .............................................. 49
Total Dry Matter ......................................... 51
Seed Production ............................ , .............. 52
Seed Study .............................................. 53
Literature Cited ................................................ 55

CHAPTER 3. DORMANCY, GERMINATION, EMERGENCE, AND SURVIVAL
OF GIANT FOXTAIL (Setariafaberi Herrm.) AND FALL PANICUM
(Panicum dichotomiflorum Michx.)

Abstract ...................................................... 66
Introduction ................................................... 68
Materials and Methods ........................................... 71
Overcoming Seed Dormancy ................................ 71
Constant Temperature ..................................... 71
Alternating Temperature .................................... 72
Seed Burial .............................................. 72
Data Anylysis ............................................ 73
Results and Discussion ........................................... 74
Overcoming Seed Dormancy ................................ 74
Constant Temperature ..................................... 75
Alternating Temperature .................................... 75
Seed Burial .............................................. 77
Literature Cited ................................................ 79

LIST OF TABLES

CHAPTER 2. GIANT FOXTAIL (Setariafaberi Herrm.) INTERFERENCE IN
NON-IRRIGATED CORN

PAGE
Table 1. 1994 and 1995 experiment establishment dates and applications ........... 57
Table 2. Rainfall and cumulative growing degree days data of the 1994 and
1995 growing season ........................................... 58
Table 3. Com yield reduction from giant foxtail density: Rectangular hyperbola
regression parameter estimates .................................... 59
Table 4. Total dry matter as influenced by giant foxtail density ................... 60
Table 5. Giant foxtail seed production as influenced by density .................. 61
Table 6. Giant foxtail cumulative seed germination as influenced by plant density. . . . . 62

CHAPTER 3. DORMANCY, GERMINATION, EMERGENCE, AND SURVIVAL
OF GIANT FOXT AIL (Setaria faberi Herrm.) AND FALL PANICUM
(Panicum dichotomiflorum Michx.)

Table 1. Cumulative germination of giant foxtail and fall panicum seeds 0, 3, 7,
and 14 days after exposure to 40 or 50 C accelerated after-ripening ........ 81

Table 2. Germination of giant foxtail and fall panicum seeds when exposed for
14 days to two photoperiods ..................................... 82

Table 3. Germination of giant foxtail and fall panicum seeds following 21
days to a constant temperature .................................... 83

Table 4. Cumulative emergence and individual plant dry weight of giant foxtail
and fall panicum following exposure of seeds to 7, l4 and 21 days at a
constant temperature .......................................... 84

vi

LIST OF TABLES (cont.)

Table 5. Cumulative germination of giant foxtail and fall panicum seeds in
petri dishes 4, 7, 14 and 21days after exposure to three
temperature regimes ........................................... 85

Table 6. Cumulative emergence of giant foxtail and fall panicum seeds from 6
planting depths 7, 14, and 21days after planting and individual plant
dry weight when exposed to three temperature regimes ................. 86

Table 7. Cumulative emergence of giant foxtail and fall panicum seeds buried
at 0, 1, 2.5, 5, 7.5, and 10 cm 7, 14 , and DAP and individual plant

dry weight ................................................... 87

Table 8. Germination of giant foxtail and fall panicum seeds buried six months
at 0, 1, 2.5, 5, 7.5, and 10 cm soil depth and then exposed to 16 hrs
20 C, 8 hrs 30 C .............................................. 88

Table 9. Characteristics of giant foxtail and fall panicum ....................... 89

vii

LIST OF FIGURES

CHAPTER 2. GIANT FOXTAIL (Setariafaberi Herrm.) INTERFERENCE IN
NON-IRRIGATED CORN

PAGE

Figure 1. Predicted corn yield reduction in 1994 and 1995 as influenced by
giant foxtail density ............................................ 63
Figure 2. Giant foxtail seed production as affected by inflorescence length .......... 64

Figure 3. Giant foxtail seed production as influenced by density .................. 65

viii

CHAPTER 1

REVIEW OF LITERATURE

INTRODUCTION

Giant foxtail [Setariafaberi (Herrm )] and fall panicum [Panicum dichotomiflorum
(Michx.)] are troublesome weeds in many agricultural crops, especially corn and soybeans
(56, 72). Both species are prevalent grassy weeds in Michigan agriculture that produce
thousands of seeds (6, 88).

There are many negative attributes associated with weeds in crops. Weeds compete
with crops for limited environmental resources, they affect crop development, and act as hosts
for pathogens and insects. Researchers note interference fi'om giant foxtail and fall panicum
reduces crop yields and profits (57, 72).

The correct weed management decisions are based on the relationship between weed
densities and crop yield loss for each specific weed species. This research investigated the
relationship between giant foxtail density and corn yield reduction, and examined difl‘erences

in seed germination and growth characteristics of giant foxtail and fall panicum

GIANT FOXTALL Setariafaberi Herrm

History and Distribution A: Setan'a species. There are more than 60 species of the genus
Setaria (84). Setaria is composed of both annual and perennial plants (46). In 1753,
Linnaeus first described the morphological characteristics of two European species of Setaria,
yellow foxtail [Setaria glauca (L.) Beauv.] and green foxtail [Setaria viridis (L.) Beauv.]
(120). Yellow foxtail and green foxtail have spread westward and established themselves as
two of the most problematic annual grass weeds in the United States and Canada (5, 7).

Twenty-eight Setaria species are native to North America, and 18 are native to the
United States (120). Today, the most troublesome species of Setaria in the United States are
giant foxtail, yellow foxtail, and green foxtail (156).

Many genus and species names may be present for a particular plant, though this
species has not tmdergone any morphological or genetic change. Initially plants in this genus
were called Setaria, but often these species were classified in the genus Panicum (64) or
Pennisetum (39). The name later was changed to Ehaetochloa, and has recently been
renamed Setaria (120).

B: Setafiafabefi. Giant foxtail is native to Asia (46, 49, 162), and was first introduced into
the United States from China through the importing of millet (47, 68). Common names
included Chinese foxtail, Chinese millet, and nodding foxtai1(7). In 1890 Herrmann publiflred
the first known morphological description of giant foxtail This description was based on a
plant collected by the Reverend Ernst Faber in the Szechwan providence of China. The first
account of giant foxtail in the United States was in Philadelphia by Long on September 9,
1931 (47, 49). Allard (3) in 1941 reported the presence of plant species known as Setaria

faberi in Virginia. In 1943 Femald (49) cited giant foxtail from Pennsylvania, New Jersey,

3

Delaware, Massachusetts, and West Virginia. Wood (162) in 1946 described a rapid and
uncontrollable spread of the Asiatic grass, Setariafaberi in North Carolina. Within the next
two years giant foxtail was reported in Tennessee, Kentucky, Missouri, Nebraska and Illinois
(46). Within 17 years after being identified in the United States, giant foxtail spread over half
the country (7). Today, giant foxtail can commonly be found in all 50 states (104). The rapid
infestation of giant foxtail has been attributed to the absence of any natural enemies (10) and
prominent seed production (114).

Fairbrothers (47) found a herbarium specimen of giant foxtail dating back to

September 19, 1925. Fairbrothers (47) speculated giant foxtail was introduced into the
United States in the 1920's within a 100-mile radius of New York City.
Morphology. Giant foxtail is in the Poaceae family. This species is described as having a
stem 0.9 to 2 meters in length branching at the base (5, 106). The leaf blades are typically 20
to 30 cm long and 1 to 2 cm in width (5, 115). Giant foxtail leaves are softly pubescent to
glabrous on the tmderside with flattened straight stiff hairs on the upper surface (5, 49). The
ligule is a dense fringe of white hairs 1 to 2 cm long and fused at the base (7). The panicle
is dense and ranges from 7.5 to 20 cm in length, bending near the base so the panicle is
drooping (106). The spikelets are 3 mm long with 3 to 6 bristles extending from the base (5,
7 ).

Giant foxtail is a tetraploid species containing 18 chromosomes (47, 115). Kishimoto
(47) studied pollen of giant foxtail plants and reported a pollen grain size for giant foxtail of
45.74 i 0.84 microns.

Growth and Development. Giant foxtail is an annual monocot that reproduces by seed only

(5). This species produces seeds on 1 to 8 individual inflorescence (panicles) per plant (41,

4
106). Seed production by individual inflorescence, which ranges from 30 to 1400 seeds (41,
114), varies with the length of the inflorescence (9, 114). Individual giant foxtail plants can
produce more than 10000 viable seeds (114).

Schreiber (114) found giant foxtail germinated and emerged early in the growing
season, although giant foxtail can germinate throughout the grong season. Schreiber (114)
concluded the earlier giant foxtail emerged, the larger the growth of the inflorescence,
resulting in increased amounts of seed per inflorescence. Continuing with this work, Schreiber
(114) documented the production of viable seeds fiom giant foxtail plants emerging as late
as August, and seed viability was not correlated with seed color.

Initially, one treatment to control giant foxtail seed production was to mow the
abovegrormd shoots. The results were mixed, as continuous cutting of giant foxtail at 6.5 cm
of top grth did prevent seed production (131), but a single cutting enabled giant foxtail
plants to produce multiple inflorescence containing viable seeds (114).

Defelice (41) and Harrison (58) reported a postemergence herbicide significantly
reduced seed produced by giant foxtail plants. Defelice (41) determined herbicides did not
change 1) the number of inflorescence produced per plant, 2) seed production per
inflorescence, or 3) the number of seeds per plant. Defelice (41) concluded that the reduction
in giant foxtail seed production fiom a herbicide application was a fimction of reducing the
total number of giant foxtail plants. Conversely Biniak and Aldrich (20) reported a herbicide
application at first anthesis reduced panicle density and seed production.

Freshly harvested giant foxtail seeds are predominantly dormant (135, 138) and
rmresponsive to light (138). Primary seed dormancy in giant foxtail seeds diminishes, through

active metabolism, when exposed to room temperatures (10). Similar effects can be achieved

5
by exposing seeds to an elevated temperature (140). Roberts (100) noted the time required
for seeds to after-ripen could be greatly reduced by exposing seeds to a temperature higher
than normal room temperature.

Initiation of giant foxtail germination is dependent upon the availability of water.
However, exposure to water stress can induce the breaking of seed dormancy (135).
Taylorson (135) found 90% of giant foxtail seeds germinated when pretreated with
polyethlyeneglycol, at a water potential of -0.3 MPa or less for 24 hours at 20 C. Similarly,
solutions of 10103 have been used to stimulate germination of weed seeds (60, 145).
Steinbauer and Grigsby (129) examined seeds of 85 species in 15 families and found halfthe
seeds tested germinated better in nitrogen rich solutions. However, Fawcett and Slife (48)
applied 112 to 336 kg ha‘1 of nitrogen as ammonium nitrate ((NH," (N 03)) to field soils and
found increasing nitrogen levels failed to affect giant foxtail germination. After primary
dormancy is broken, exposing giant foxtail seeds to temperatures greater than 30 C (136) or
exposure for 7 days or longer to 60 C will induce a secondary seed dormancy (135).

Germination and growth of giant foxtail are temperature dependent (158). The
estimated mininmmtemperature to initiate giant foxtail growth is 10 C (79, 90). Stoller and
Wax (133) examined the variation in temperature within the surface layers of soils, and
determined soil surface temperatures are affected by soil type. Temperature affects the
growth of giant foxtail seedlings by altering plant biomass and the date of tiller initiation (81).
Mester and Buhler (79) examined the effects of soil temperature on giant foxtail seedling
development and reported lack of giant foxtail seed germination at 5 C, and concluded soil
temperature did not affect seedling development.

Giant foxtail seeds will germinate and emerge fiom a wide range of planting depths

6
(80, 107). Mester and Buhler (80) analyzed giant foxtail emergence under field conditions
in a no-tillage system and noticed half the emerged seedlings originated from a depth of 1 cm
or less. They proposed a giant foxtail seedling survival rate of 100% if weeds germinated on
the soil surface (79). Field studies conclude the maximum depth giant foxtail seeds can
emerge from is 10 cm (80, 107, 138).

Schreiber (113, 117) exposed giant foxtail seedlings to various air temperature and
photoperiods to examine their responses. Giant foxtail plants produced the most dry weight
when exposed to an air temperature of 27 C. Schreiber (113, 117) also noted that longer
photoperiods increased inflorescence length Knake (69) studied the effects of shade on giant
foxtail development and reported seed weight, plant dry weight, leaf number, stems per plant,
and heads per plant decreased linearly with increased shade intensity. However, with 30%
shade, mature inflorescence were longer than in plants grown without shade (69).

Mechanical removal of giant foxtail can be successful in controlling giant foxtail, but
if the stems are not completely covered during the cultivation, rerooting can occur (107).
Santelmann et al. (107) found that when given an opportunity, the main stem or first tillers
of a giant foxtail seedling reroot 75% of the time, and half of the second and third tillers can
reroot.

Giant foxtail plants produced tillers 10 to 20 days after emergence and continued to
produce tillers up to 3 months after emergence (107 ). Average giant foxtail plants produced
between 7 and 15 tillers (107). The total number of tillers produced per giant foxtail plant
was reduced by increasing plant densities (107). The date of emergence also affects the
number of tillers produced per plant, as late germinating giant foxtail plants produced fewer

tillers (107 ).

7
Habitat. Giant foxtail is extremely troublesome in disturbed soils, row crops, spring seeded
alfalfa and small grains, and along roadsides and in waste areas (5, 7, 156).

Schreiber (112) examined the competitiveness of various foxtail grass in undisturbed
sites. Schreiber (112) studied robust white foxtail (Setaria viridis var. robusta-alba), robust
purple (Setaria viridis var. robusta-pwpurea), giant green foxtail [Setaria viridis var. major
(Gaudin) Posp.], yellow foxtail, and giant foxtail for four years to decide whether all Setaria
species posed the same threat to infest fields as giant foxtail. Schreiber discovered that
despite the Setaria species planted, within four years of planting, giant foxtail was the
dominant species. Similarly, Staniforth (122) conducted research on the competitive effects
of giant, yellow, and green foxtail and discovered giant foxtail grew more vigorous and

reduced soybean yields more than yellow or green foxtail.

W Panicum dichotomzflorum (Michx. ).

History and Distribution. Fall panicum is an annual grass in the genus Panicum. The genus
Panicum is quite complex as it comprises more than 200 species (108). Fall panicum is native
to North America, but has become a specific problem in field crops in the last 30 years (6).
Today, the most common Panicum species in North America are fall panicum, wild proso
millet [Panicum miliacea (L. )], and witchgrass [Panicum capillare (L. )]

Fall panicum was first described by Ada George in 1914 (93, 108). Traditionally, this
species was called Western witchgrass (156), wild millet, sprouting panicgrass, sprouting
crabgrass, kneegrass, and spreading panicum (93). Gray in 1950 described fall panicum as
a species native fiom Maine to Nebraska and Florida to Texas (93 ). Vengris (149) conducted

a survey in Massachusetts in 1950 and found farmers only considered fall panicum a weed in

8
cranberry bogs. A 1970 survey concluded fall panicum was a serious problem in 23 states
(108). By 1975 fall panicum was present in 43 states, and a serious problem in 32 states
(108). Today, fall panicum is found throughout the United States.
Morphology. Fall panicum is in the Poaceae family. This species is described as having an
upright or spreading grth habit, up to 1 m in height (166). The leaf blades are 5 to 40 cm
long and 0.5 to 1.5 cm in width (5). The leaves are usually hairless and contain a predominant
white midrib. The ligule is a dense fiinge of white hairs 1 to 2 mm long and fused at the base.
The inflorescence is an open panicle. The spikelets are hairless and 1.8 to 3.6 mm long (7,
166).
Growth and Development. Fall panicum is an annual monocot that reproduces by seed only
(5). Seeds are produced on 1 to 52 panicles per plant, depending on the time of emergence
(148). A typical fall panicum plant, growing under field conditions, produces 500000 seeds
(147).

Research has shown the greatest emergence of fall panicum occurs when seeds are
buried 0.2 to 2.0 cm (147, 166). Maximum emergence for buried fall panicum seed is 7 cm
(2, 148).

Fall panicum seed dormancy is not easy to overcome (137). Fall panicum seeds
require an exposure to temperatures greater than 25 C for 9 to 21 days for germination (147).
Freshly harvested fall panicum seeds are typically dormant (23 ). Fall panicum seeds require
light exposure to induce germination (12, 137, 155). Dormancy can be overcome by
exposing seeds to high temperatures, alternating temperatures, stratification, and mechanical
or chemical scarification (137).

Vengris (147) studied the growth habits of fall panicum He noted the number of

9

days, from emergence to flowering decreased progressively for later emerging fill panicum
seedlings. Fall panicum seedlings emerging on May 23 and July 25, produced ripe seeds in
116 and 74 days, respectively. He concluded fall panicum plants can adjust their growth rate
dependent on time of emergence. Vengris (147) also documented fall panicum seedlings
emerging between June 23 and July 7 were the most vigorous and fastest grong plants in
Massachusetts, and noted fill panicum plants emerging after August 9 were unable to produce
ripe seed.

The use of specific herbicides has often been associated with the development of fill
panicum infestations (63, 91, 141). Thompson et al. (142) compared the ability of fill
panicum and giant foxtail to metabolize atrazine [2-chloro-4-(ethyl-amino)—6-
(isopropylamino)-s-triazine]. In 6 hours, corn, fill panicum, and giant foxtail metabolized 96,
44, and 7%, respectively, of the 1“C atrazine applied. Thompson (141) reported conjugation

of atrazine with peptides resulted in detoxification in fill panicum

WEED INTERFERENCE PRINCIPLES

Weed Ecology. A weed was defined by the terminology committee of the North Central
Weed Science Society of America in 1956, as a plant growing where it is not desired (66).

Approximately 250 of the more than 200000 plant species in the world, are suficiently
troublesome to be called weeds (97). Holm (62) classified these 250 species by fimilies and
formd nearly 70% of these weed species fall into 12 fimilies, and 40% of these weeds are in
either the Poaceae or Compositae family. Holm also categorized the most commonly found
crops. He revealed that common crop fimilies contribute many problematic weeds. Holm

(62) concluded crops and weeds ofien share some taxonomic characteristics and perhaps a

10
common evolutionary origin (62).

Weeds are grouped by many different classification systems. These systems include
grouping weeds by their habitat, ease of control, degree of undesirability (noxiousness), and
morphology. The most common method to classify weeds involves the plant’s life cycle (7 ).
This classification system groups weeds as annual, biennial, and perennial plants. Annual
plants complete their life cycle (seed to seed) in one year or less (97 ). Annuals are the largest
and most troublesome segment of weeds throughout the world (97). Biennial plants require
two years to complete their life cycle (31). Few biennial species are problematic weeds in
agriculture systems (31). Perennial plants live for more than two growing seasons (7 ).
Weed Interactions. Plant interactions are complex and occur in natural plant communities
and highly managed agricultural systems. Dewet and Harland documented plants respond
differently when their habitats are disturbed (97 ). When the environment becomes altered,
certain species flourish while others migrate or are replaced. Interactions between
neighboring plants subsequently affect both species growth (either positively or negatively).
Burkhold and Odum categorized the interactions between plants growing together. Both
described an interaction between neighboring plants that is neither positive nor negative as
neutralism Neutralism occurs when two simultaneously grong species are neither
negatively nor positively afi‘ected by the presence or growth of the other species (10).

It has been documented that specific weeds and crops, for example bamyardgrass
[Echinochloa cms-galli (Beauv. )] and rice (97), seem to grow with one another. The
association between bamyardgrass and rice may be explained by one of the three positive
interactions (commensalism, protocooperation, and mutualisrn) (121). Commensalism is an

interaction where one plant is stimulated by the presence of the other, and inhibited by its

1 1

absence (26). Protocooperation is a more common interaction where both plants are
stimulated by the association, but are unaffected by the other absence (26, 97). An example
of protocooperation is where fungal hyphae link two or more plants to ficilitate nutrient
uptake (163). Mutualism contrasts the other positive interactions in that it is an obligate
interaction, meaning without the presence of both species, the growth of both species will be
limited (26).

0f the interactions described by Burkhold and Odum, amensalism and competition are
the most common. Both amensalism and competition display negative efi‘ects on plants.
Amensalism is an interaction in which one plant is negatively affected by the other, whereas
the grth of the second species remains constant (26, 97). The inhibition of one plant
through the release of a selectively toxic by-product, which is known as allelopathy, is a form
of amensalism (97).
Allelopathy. Specific plant residues contain allelopathic compounds (18, 116, 117). Natural
compormds exist in plants to ensure species survival (10). Allelopathic substances reach the
soil through the leaching of soluble compounds fiom plant decay (130). Allelopathic
compounds, once in solution, can be taken up by a plant root system (19, 130). Bhowmik
and Doll (19) conducted research on corn and soybean response to allelopathic effects of a
weed residue and concluded allelopathic effects were dependent on the amount and
concentration of weed residues.

Ecologically, giant foxtail and fall panicum are not the most competitive species for
light, moisture or nutrients, which suggests an allelopathic substance would enable a
competitive advantage to allow room for growth (117). Residues fiom mature giant foxtail

and fall panicum plants contain compounds that affect corn (Zea mays) root development

12
(117) and growth (18, 117). Applying a 1% (w/v) giant foxtail and fill panicum residue
extract reduced corn radical elongation 28 and 27%, respectively (19). Bell and Koeppe (18)
noted giant foxtail residues inhibited corn growth by 35%.

Researchers have observed the selective nature of the inhibitors exuded from giant

foxtail plants (18, 19). Bhowmik and Doll exposed soybeans [Glycine max (L.) Merrill]
seeds to extracts from giant foxtail residues and found no effect on hypocotyl extension.
Competition. Competition is the mutually adverse efi‘ect to organisms that use a common
resource in short supply (10). Competition can be separated into two major categories, 1)
interspecific competition, and 2) intraspecific competition. Interspecific competition involves
the interference between plants of difi‘erent species, whereas intraspecific competition is the
interaction between plants of the same species (97). The level of competition is influenced
by plant density (110). Competition within a specific ecosystem occurs when the population
exceeds the required level needed to sustain optimal growth. Any resource that affects plant
growth or survival potentially can influence competition between weeds and crops (69, 157).
Physiologically weeds and crops are similar, and compete for environmental fictors needed
for growth and development (38, 39). Typically the most limiting resources for plants in an
agricultural system are light, water, nutrients and CO2 ( l, 37).
Light and Shade Stress. The primary environmental resource in which weeds and crops
compete for is light (169). Light, unlike other limited resources, does not have the capacity
to be stored or transferred within the plant (1). When a photon of light contacts the surfice
of a plant the energy is either converted to chemical energy through photosynthesis or
dissipated as heat (1).

Studies have examined the effects of light on the germination (118, 139, 153, 154,

1 3

155) and development (69) of weeds and crops. Many weed seeds require light for
germination (51, 139). Phytochrome is a proteirraceous pigment that is the determining factor
in the germination of light sensitive seeds. Phytochrome occurs in two forms within plants;
P, and Pf, Numerous seeds display a dependence on a specific light to induce germination
(139). Germination of phytochrome sensitive seeds requires a conversion of phytochrome
to the active Pf, form by exposing the seeds to red (650 nm) light (39). The germination of
phytochrome controlled seeds is prevented by increasing the ratio of P, to P,, (40). Light
reaching the soil surfice, once canopy closure has occurred, typically has a high ratio of fir-
red to red light (51, 97). Because this light is high in far-red light, it converts phytochrome
to the inactive (P,) form that prevents the germination of phytochrome sensitive seeds.

Taylorson (139) studied phytochrome controlled changes in the germination of both
giant foxtail and fill panicum seeds. Fall panicum seeds displayed an effect, where exposure
to red light converted P, to P, and induced germination. Small increases in P, levels account
for most of the fall panicum germination (139). The data on giant foxtail is less clear, as an
increase in P, levels only increased giant foxtail germination, slightly (40). Taylorson (139)
concluded that giant foxtail seed germination may be depend upon another mechanism, such
as a cyclic germination pattern, to break seed dormancy rather than the reliance of
phytochrome. Similarly, Roberts and Feast (102) examined numerous weed seeds and found
in many seeds a peak in germination during the spring.

Research has been conducted to determine the effect shade has on plant grth and
development. Researchers have formd that both com (88) and soybean (28, 122, 123) growth
and development were reduced by shading.

Water Stress. Lack of water is one of the common environmental factors limiting crop

14

growth and yield (157, 169). Researchers consider water the environmental resource most
limiting crop growth and yield (17, 92). Water stress occurs when transpirational water loss
exceeds water uptake (103 ). Weeds compete with crops for water and contribute to crop
water stress (169). Water use efficiency, transpiration rate, and response to declining water
availability vary between weed species and crops ( l, 92, 97, 160). This variance accounts for
differences in the level of crop yields lost by competing weeds of different species (89, 92).
Researchers have focused on the effect water stress has on corn yields (103). Studies
conclude moisture is most critical during silking. If corn is under moisture stress at the time
of silking, grain yields can be reduced by 50% or more (32, 42, 61, 103).

Water stress also influences the duration of the critical weed-free period. Coble et al.
(33) reported the critical weed-free period of common ragweed [Ambrosia artemisiifoilia
(L. )] in soybeans was two weeks in a dry year and four weeks in a year where moisture was
readily available. However, a study in Illinois noted giant foxtail reduced soybean growth
after 10 days when soil moisture was abrmdant, but significant growth reduction was delayed
until 25 days afier emergence during a drier year (58). Staniforth (124) reported weed
interference reduced soybean yields 5% when soil moisture was adequate during the entire
growing season, but when soil moisture was adequate until July and then became limited,
soybean yields were reduced 15%.
Nutrient Stress. Nutrient availability alters the level of interference between weeds and
crops through its differential effects on grth (37, 94). Weed growth can be stimulated
more than crop growth fiom an application of fertilizer (149). Weeds are often more
competitive with crops at high fertility levels (94, 124). Vengris et al. (149) studied the

response of com yields from phosphate fertilizer. Corn yields in 1952-53 were higher when

15

no weeds were present. However, in 1952, yields were lower when the corn was fertilized
with 200 lbs. of P205 /A (149). Vengris et al. (149) concluded increased rates of fertilizer
cannot maintain corn yields in the presence of weeds.

Staniforth (124) examined the effects of weed interference in four corn hybrids in
1958 and 1959. Yield reductions in the later maturing hybrids were double those of the early
manning hybrids, and yield reductions for all the varieties were greatest under high nitrogen
fertilization. However, research has formd the interference by yellow foxtail can be overcome
by adding nitrogen to com (125). Research at Cornell University (43) examined strategies
to reduce crop yield loss from weed competition. Fertilization timing, cultivar selection, weed
control practices, and row spacing are fictors that can be altered to enhance crop nutrient use
efficiency.
CO2 Stress. Plants can be categorized by their photosynthetic pathway of CO2 fixation.
Yield and grth of plants depends on carbon assimilation by the photosynthetic process
(21). The most common procedure for weeds to fix CO2 is through the 3-carbon pathway
or Calvin Cycle (134). Plants using the 3-carbon pathway are called C3 plants. Plants fixing
CO2 by producing a 4-carbon compound, oxaloacetic acid, instead of a 3-carbon PGA, are
referred to as C4 plants. Each of these CO2 fixation schemes can be beneficial. C3 C02
fixation allows plants to more efficiently manage their CO2 intake (39). However, when C3
and C, plants are grown under a stressful environment, C4 plants have photosynthetic rates

two to three times higher than those of C3 plants (134).

INTERFERENCE RESEARCH

Losses in crop quality and yield from interfering weeds are the backbone of modern

16
weed science (75). Numerous factors influence the level of crop loss fiom competing weeds
(96). Interactions between weeds and crops are often complicated and difficult to determine
the exact component limiting crop yield (110). The term interference should be used where
one cannot determine the exact cause of crop yield loss. Agricultural scientists often misuse
the term competition to describe interference (110).

There are four generally accepted designs to examine crop and weed interactions (35,
96). Each design accounts for the density, and spatial arrangement for each species (32). The
most common designs are additive, replacement, systematic, and neighborhood (96). Each
design is a form of a bioassay where the response of one species is used to describe a change
within another species. Crop yields, growth rate and mortality are measured in each of these
designs (96).

The most common design for interference studies is an additive design (35, 169). In
this design the density of one species, most commonly the crop, is held constant, whereas the
darsity of the second species varies between treatments (35). This design is popular because
it most resembles an agricultural system (35). An additive design is suited for objectives
involved with determining the crop yield loss from a specific weed density, multiple species,
and when determining an economic threshold for weed control The intraspecific competition
in an additive design study is assumed to be zero because the spatial arrangement of the crop
is uniform However, the interspecific competition is often unknown because the placement
of the weeds is often unrecorded (35). The additive design has been criticized because, in
multiple species experiments, it does not account for the variability in the number of each
species (55). Total weed density and the proportion between species often vary in a multiple

species additive design study, making the interpretation of the data difficult (35).

17

In a replacement series design the density of the two species varies but the total
density remains constant. In this design pure stands of each species are included in the
experiment (96). The replacement series design determines the level of yield reduction in
crops by comparing yields with the yields of weed-free stands (37). A replacement series
design is appropriate when determining the competitive effects of a single species. The
advantage of a replacement series design is that it determines the effects of intraspecific and
interspecific competition (96). The criticism of this design is that it is artificial for field use
because crops are planted at a constant population (35).

Systematic designed experiments study a single species by arranging the plants in a
circular or arc pattern (96). The area in which plants have to grow changes between
treatments in a systematic experiment (37). The advantage of this design is several different
plant densities can be studied within a small area. However, placing a circular pattern in a
field setting is often dificult. Another disadvantage of this design is that only individual
plants can be measured, making it difficult to determine how neighboring plants effect growth.

In a neighborhood design experiment the attention is placed on how an individual
plant responds in conjunction to neighboring plants. The advantage of this design is that it
becomes possible to study the exact time competition begins to occur (96). Typically, the
performance of the target plant depends on the number, biomass, and the distance between
its neighboring plants (96).

The proper analysis for each of these designs starts with knowing the objective of the
study. Different objective require difl‘erent designs. A researcher first must state their
objectives to design an interference study properly (32). According to Cousens (35), if the

design and analysis of an interferarce experiment are based on the objectives of the study, and

18

the proper design is implemented within its limitations, the results will be meaningful.

WEED INTERFERENCE

Numerous interference studies report crop yields are lowered by competing weeds

(13, 22, 33, 87, 134, 152). Researchers have investigated the effects of weeds and crop
density on com yields (105, 144, 149, 167). Zirndahl (169) and Stewart (136) cite more than
500 publications describing the outcome of various weed and crop interactions. The
relationship between crop yield and plant density is of considerable interest (143). Difi‘erent
models have been developed to observe the interactions between crops and weeds, and
considerable success has been achieved in finding empirical expressions that fit data from a
variety of experiments.
Broadleaf Weeds. Researchers have investigated the level of interference in crops fiom
weeds for more than 40 years (127). It is the opinion of many researchers that a specific yield
loss frmction is correlated to, 1) the duration of the interfering weeds, and 2) the yearly
environmental fluctuations (16, 52, 119, 126, 127, 168).

Cardina et al. (30) studied the competitive effects of velvetleaf [A butilon theophrasti
(Medilc )] in conventional and no-tillage corn. The main plots of these experiments were
divided into two subplots, where either the velvetleaf seeds were planted simultaneously with
corn or three weeks after the corn. The subplots consisted of four rows of corn with
velvetleaf densities of 0, 1, 5, 10, 20, and 30 plants m". The greatest reduction in corn yields,
using the rectangular hyperbola model discussed by Cousens (35), resulted when the
velvetleaf emerged early in a no-tillage system. Cardina et al. (30) reported the asymptote

(A), which represents the maxirmun yield reduction, ranged from 17% in conventional tillage

19
in 1992 to 69% in no-tillage in 1990.

Cardina et al. (30) also developed an economic threshold level for velvetleaf in com.
The economic threshold ranged from 0.13 velvetleaf plants m’2 for early emerging velvetleaf
in no-tillage to 18.2 rn'2 for late emerging velvetleaf in conventional tillage. Difi‘erences
between economic threshold values for early and late emerging velvetleaf varied with year and
tillage. They concluded, that without reliable data on the biology of velvetleaf; a velvetleaf
economic threshold in corn was difficult to predict. They stated the need for research
focusing on understanding velvetleaf seed survival and production.

Lindquist et a1. (75, 76) examined the level of interference fiom velvetleaf in soybeans.
They found in 1992 and 1993 soybean yields were not significantly reduced by 32 and 45
velvetleaf plants m'z, respectively. Other researchers have reported velvetleaf substantially
reduced soybean yields (40). Schmenk (110) reported a significant corn yield reduction in
Michigan occurred at a velvetleaf density of 9 plants per m of row in 1992, and 1 plant per
m ofrow in 1993.

Lindquist et al. (75) developed a model to predict the population dynamics and
economics of velvetleaf control in a com-soybean rotation. Similar to Cardina et al.,
Lindquist et al. (7 5) indicated the primary wealmess of their model is the limited biological
data available on the grth and development of velvetleaf

Moolani et al. (85) studied the competitive efi‘ects of smooth pigweed [Amaranthus
lybridus (L. )] on corn planted in 102 cm rows Untreated smooth pigweed in a 15-cm band,
reduced corn yields 30, 50, and 36% in 1959, 60, and 61, respectively. Moolani et al. (85)
concluded that whether the total dry matter for each plot consisted of corn alone or corn and

weed biomass, the total dry matter accumulation remained constant.

20
Beckett et al. ( 16) studied the level of interference of common cocklebur [Xanthium
stmmarium (L. )], common lambsquarters [Chenopodium album (L. )], shattercane [Sorghum
bicolor (L. )], and giant foxtail. Beckett et al. (16) reported a common cocklebur density of
5 plants per m of row decreased corn yields in Illinois 27% in 1985. In 1986 and 87, com
yields were reduced 10% fiom 7 common cocklebur plants per m of row. Common
lambsquarters, shattercane, and giant foxtail only significantly reduced com yields in one of
the three years tested. In 1985, corn yields were reduced, 12% fiom 5 common
lambsquarters plants per m of row, 22% from 17 shattercane plants per m of row, and 18%
from 85 giant foxtail plants per m of row ( 16). Other researchers found untreated infestations
of common cocklebur reduced soybean yields as much as 52% (l 1). Similarly, 208 common
lambsquarters (119), 60 shattercane (59), and 180 giant foxtail (72) plants per m of row have
reduced corn yields by as much as 58, 75, and 26%, respectively.
Grass Weeds. Young et al. conducted field studies to evaluate the efi‘ects of quackgrass
[Agropyron repens (L.) Beauv.] interference on soybean (168) and com (167) yields. They
reported a 19 and 55% reduction in soybean yields by quackgrass densities of 520 and 910
shoots m‘z, respectively. Interference by a natural stand of quackgrass for 6 weeks, 8 weeks,
and full-season decreased soybean yield 11, 23, and 33%, respectively. Analysis of corn
tissue suggested quackgrass did not interfere with the nutrient status of corn. Young et a1.
concluded that a sufficient supply of soil moisture can overcome the effects of quackgrass
interference on corn yields if light and nutrients are not limiting.
Wilson and Westra (161) studied the effects of wild proso millet interference in
irrigated com yields. Interference by wild proso millet for 2 and 6 weeks after corn planting

reduced corn yield 10 and 24%, respectively. Corn yield reductions, predicted with a

21
rectangular hyperbola regression model, ranged from 13 to 22% fiom a wild proso millet
density of 10 plants rn'2 (161).

Peterson and Nalewaja (94) examined the effects of green foxtail interference on the
development of spring wheat. Wheat fiesh weights were reduced 50% by green foxtail
seeded four days before wheat seeding. However, fiesh weight was only reduced 13% by
green foxtail seeded four days after wheat. Peterson and Nalewaja (94) also reported
doubling the nitrogen and nutrient concentration did not increase wheat growth, but
significantly increased green foxtail fiesh weight.

Sibuga and Bandeen (119) conducted field experiments to study the effects of full-
season interference of green foxtail and common lambsquarters on corn yield. Corn yield
reductions were observed at densities greater than 56 and 20 green foxtail plants m‘2 and 46
and 109 common lambsquarters plants m'2 in 1976 and 1977, respectively.

Nieto and Staniforth (88) examined the interference of yellow foxtail and green foxtail
on corn yield. A three-factor field study was conducted to determine the efi‘ect’s nitrogen,
and weed density had on com yield Adding, 0, 70, and 140 pounds of elemental nitrogen per
acre resulted in a com yield reduction of 20, 14, and 10 bushels per acre, respectively. They
concluded that the addition of nitrogen fertilizer to corn generally overcame yield losses from
heavy foxtail infestations.

Giant Foxtail. The extent in which grain is lost fiom interfering giant foxtail plants is
dependent upon its duration. Gleason (52) noted the longer giant foxtail plants were present,
the more crop yields were suppressed. Knake and Slife (70) examined the effect of time of
giant foxtail removal fiom corn and soybeans in 1963 to 1965. Giant foxtail reduced corn

yields 63, 126, 315, 441, and 1133 kg ha'1 and soybean yield 0, 0, 63, 126, and 1133 kg ha",

22
respectively, when removed at 7.5, 15, 22.5, and 30 cm in height and at maturity. Knake and
Slife (70) also reported total dry matter remained constant whether the dry matter consisted
of a weed-free crop or a crop and giant foxtail.

A field study by Knake and Slife (68, 71) investigated the level of interference from
giant foxtail seeded when the crop was planted and 3, 6, 9, and 12 weeks after planting.
Giant foxtail seeded with the crop reduced com and soybean yields 13 and 27%, respectively.
They formd giant foxtail plants seeded 3 weeks after the crop did not significantly reduce corn
or soybean yields.

Knake and Slife (72) conduced a three-year giant foxtail interference study in Illinois
utilizing com and soybeans planted in 102 cm wide rows. Interfering giant foxtail plants
reduced corn yield, cob weight, ear weight, stalk diameter, soil temperature, and soybean
yield and pod number. Corn and soybean yields, from 180 giant foxtail plants per m of row,
were reduced 25 and 28%, respectively. Giant foxtail plants did not affect corn or soybean
grain moisture content, crop height, and oil or protein content of soybeans.

Harrison et al. (58) studied the interference and control of giant foxtail in soybeans.
They reported every chimp (3-6 plants) of giant foxtail plants per 9 m of row, reduced
soybean yield 0.8%. They estimated 10 giant foxtail plants per m of row reduced soybean
yield 16%.

Langston and Harvey (74) designed a giant foxtail interference study using alachlor
impregnated on dry fertilizer to create varying densities of giant foxtail. Thirty giant foxtail
plants per m of row did not reduce corn yield in 1993. However, 30 giant foxtail plants per
m of row reduced com yield 18% in 1994. Similarly, Lambert et a1 (73) reported comparable

giant foxtail densities reduced corn yield 0 to 20% in 1993, and 15 to 52% in 1994.

23

Walker and Williams documented giant foxtail interfered with the growth and
development of a container grown bush cinquefoil [Potentilla fiuticosa (L. )] (150) and
Bailey's redosier dogwood (Camus x baileyi) (151). Bush cinquefoil shoots dry weight
decreased up to 75% after 83 days of interference fiom giant foxtail. A growth reduction in
Bailey's redosier dogwood was noted 21 days after transplanting giant foxtail seedlings into
the containers.
Fall panicum. Harris and Ritter (56, 57) studied the effects of a natural stand of fall panicum
and giant green foxtail on soybean. Plots maintaining weed free for 2 weeks after soybean
emergence produced yields equaling plots maintained weed free the entire growing season.
Harris and Ritter (57) noted fall panicum and giant green foxtail growmg naturally with
soybeans for 8 weeks after soybean emergence did not reduce yields. However, soybean
yields were reduced if fill panicum and giant green foxtail were not removed after 8 weeks.

Ambrose and Coble (4) investigated the effects of fill panicum interference on
soybean yields and found 0.3, 0.5, 1.7, and 6.7 fill panicum plants per m of row reduced
soybean yields 1, 5, 15, and 15%, respectively. Soybean yields were not significantly reduced
if fall panicum was removed within 10 weeks after soybean emergence or if soybeans
remained weed free 2 or more weeks after emergence.

York and Coble (165) reported I fill panicum plant per 4.9 m of row reduced peanut
[Arachis hypogaea (L.) 'Florigiant'] seed yield 25%. They also detected peanut seed yields
was reduced less by fill panicum interference if establishment was 2 weeks after peanut

emergence.

24
SEED LONGEVITY

The rate at which the percentage of viable seeds decreases is dependent on several
factors (101). Egly and Williams (45) reported 61 to 88% of weed seeds emerge during the
first year and 9 to 23% emergence during the second year. In contrast Forcella et a1.
concluded the percentage of seasonal emergence ranged from 0.1% to 30%. There is
extensive evidence to show seeds of many weed species remain viable for long periods when
buried in undisturbed soil (99). Dawson and Brans (32) examined the longevity of weed
seeds and determined subtle differences in environmental conditions had an extreme affect on
seed longevities. In 1879, Beal buried weed seed in glass bottles with soil (36). Yellow
foxtail seeds remained viable 30 years after burial.

Researchers note weed seeds are commonly lost by germination, predation, and

pathogenetic attacks (95). Roberts (100) found the total viable seed population in soil
declined at a rate leaving the number of seeds present in 1 year, approximately halfthat of the
previous year.
Tillage. Farmers in the mid-1960's considered no-tillage as a way to cut production costs,
achieve more timely planting, and lessen soil erosion losses (54). Today, no-tillage cropping
systems can produce com yields equal to or higher than yields obtained in conventional tillage
systems (44, 53).

Mohler (83) developed a model that predicts the density of weed seedlings that will
emerge by relating 1) the capability of seedlings to emergence, 2) seed survival, and 3) burial
depth This model assumes, in the first year following seed input, no-tillage will have more
seedlings than tillage (83). No-tillage, in later years, will provide fewer seedlings unless seed

dormancy is high or seed survival near the soil surface is unexpectedly high.

25

Tillage affects many factors determining the initiation of weed seed germination.
Johnson and Lowery (65) reported the maximum difference in daily temperature observed
between no-tillage, chisel, till-plant, and conventional tillage occurred on May 2, 1982. They
documented a 5.9, 2.3, and 1.8 C reduction in soil temperature at 5 cm depths between no-
tillage, chisel, and till-plant when compared with conventional tillage. The reductions in soil
temperature observed with conservation tillage practices was attributed to difi‘erences in
thermal admittance, heat flux to deeper depth, and total heat inputs to the soil surface.

Staricka et al. (128) traced the vertical distribution of weed seed in different tillage
systems The maxinnrm depth weed seeds were buried under a chisel and conventional tillage
was 12 and 32 cm, respectively. Similarly, 50% of the seeds in chisel systems were within 4
cm of the soil surface, compared with 10% in conventional tillage (128). Researchers found
a marked increase in annual grass densities in no-tillage systems, but no change in annual
broadleaf species (25, 164).

Wiese and Birrning ( 159) examined the effect tillage date has on the initiation of seed
germination. Yellow foxtail was the predominant species after the first tillage timing, but
emergence decreased with delayed tillage (159). Weeds that emerged early in the growing
season were common lambsquarters and ladysthumb [Polygonum persicaria (L. )]. Redroot
pigweed [Amarcmtlms retroflexus (L. )] was a poor competitor early, but by June 24 was the
fastest growing species.

A: Giant Foxtail. Giant foxtail emergence is often greatest fiom seeds at or near the soil
surfice, and decreases as depth of seeding increases (39). Buhler and Daniel (25) noted as
tillage decreased, depth of giant foxtail germination decreased and density increased.

Schreiber (111) examined tillage effects on giant foxtail population dynamics.

26

Reducing tillage fiom conventional to no-tillage increased giant foxtail seed in the top 0 to
2.5 cm of soil (111). Becker and Staniforth (15) found disturbing the top 2.5 cm of soil
resulted in a 30% increase in giant foxtail density. Buhler and Mester (24) reported 40% of
giant foxtail plants originated in the upper 1 cm of soil in no-tillage compared to 25% in
chisel, and 15% in conventional tillage, and reported giant foxtail control, with the same
herbicide treatment, was often less under no-tillage systems.
B: Fall panicum. Researchers conclude under various tillage systems weed spectrums shift
rapidly (31, 146). Buhler and Daniel (25) noted the weed spectrum shift in no-tillage is
dependent upon the original species present and the herbicide used. Triplett and Lytly (146)
determined in no-tillage corn, fall panicum was the most problematic annual weed where
triazine herbicides were used. Bauman and Ross (14) reported previous corn crop residues
prevented as much as 30% of the atrazine fiom reaching the soil surfice. Long-term use of
atrazine in North Carolina was associated with replacement of large crabgrass [Digitaria
sanguinalis (L.) Scop.] by fall panicum (34). Williams and Wicks (159) observed a shift in
annual grass species, in no-tillage systems, fiom Setaria species to fall panicum
Predation. Ground cover has shown to provide weed suppression and provide a habitat for
seed predators. Researchers have documented post-dispersal seed predation reduces both
seed supply and seedling emergence in old fields, pastures, and grasslands (86, 98). Reader
(98) conducted a field experiment on seed losses fiom predation. Reader (98) concluded
ground cover limits seedling emergence by providing a habitat for seed predators.

Mittleback and Gross (82) conducted studies in old field habitats in Michigan to
determine the rate seeds are lost to post-dispersal predators. Seed removal by predators was

higher in vegetated habitats than in areas of disturbed soil. Mittleback and Gross (82)

27
reported up to 20% of the seeds in undisturbed vegetation were removed in one day.

Marino et a1. (78) studied the association between the distance from hedgerows and
the amount of seeds lost by predation. Most weed seeds lost by predation occurred
overwinter (7 8). Marino et al. (78) concluded the distance from hedgerows did not affect
seed losses.

Lund and Turpin (77) examined the affinity of four species of Carabidae beetles to
various weed seeds. They reported the preference for one weed seed over another maybe due
to the ease of opening rather than selection based on textural or chemical seed qualities. The
size and shape of the weed seeds affect the easy in which the beetles can open the seeds. This
idea would explain why only 7% of the smaller fall panicum seeds were damaged by beetles,
while 54% of the larger giant foxtail seeds were damaged.

Seedbanks. The weed seedbank, containing viable seed in the soil or on its surfice, is the
primary source of annual weeds. Reducing the size of the weed seedbank is a long-term goal
of weed management (29).

Ball (8) evaluated the effects of tillage, herbicide use, and crop rotation on weed
species changes in the soil seedbanks. Crop rotation was the dominant factor influencing
species composition in the seedbank. Ball (8) accounted this to herbicides shifting the weed
spectrum to favor species less susceptible to the applied herbicide.

Determining the initial density of viable seed in the soil seedbank is critical for
bioeconomic weed management models (67, 109). Bioecononric models can devise a weed
control strategy, based on seedbank numbers, necessary to provide season-long weed control.
Forcella et al. (50) examined seedsz and seedling emergence of annual weeds in

agricultural fields at eight locations in the corn belt. Percent viable seeds, emerging as

28
seedlings, ranged fiom less than 1% for yellow rocket [Barbarea vulgaris (R Br. )] to 30%
for giant foxtail This information is a necessity in developing a reliable bioeconomic model

for predicting weed seed emergence.

10.

ll.

12.

13.

29

LITERATURE CITED

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Publishers, North Scituate, MA 465 pp.

Alex, J.F. 1980. Emergence from buried seed and germination of exhumed seed of
fall panicum Can. J. of Plant Sci. 60:635-642.

Allard, HA. 1941. Some plants found in northern Virginia and West Virginia.
Virginia J. Sci. 2:119.

Ambrose, L. G. and H.D. Coble. 1975. Fall panicum competition in soybeans.
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Anonymous. 1981. We; North Central Region
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Anonymous. 1972. Panic(um) in Ontario. Weeds Today. 3(3): 16.

Anonymous. 1970. el We f h nit Agriculture Handbook
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Ball, DA 1992. Weed seedbank response to tillage, herbicides, and crop rotation
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Barbour, J .C., III., and F. Forcella. 1993. Predicting seed production by foxtails
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Barbour, M.G., J.H Burk, and W.D. Pitts. 1987. MW, 2“d ed.
Benjamin/Cummings Publishing Company, Inc., California. 105-154 pp.

Barrentine, W.L., 1974. Common cocklebur competition in soybeans. Weed Sci.
22:600-603.

Baskin, J.M. and CC. Baskin. 1983. Seasonal changes in the germination
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optimum thresholds for two annual weeds in soybeans. Weed Technol. 62228-235.

Bauman, T.T. and MA. Ross. 1983. Effect of three tillage systems on the
persistence of atrazine. Weed Sci. 23:512-515.

Becker, RL. and D.W. Staniforth. 1979. Effects of soil disturbance on weed
seedling establishment. Proc. North Cent. Weed Sci Soc. 34:43.

Beckett, T.H., E.W. Stoller, and L.M. Wax. 1988. Interference of four annual
weeds in corn (Zea mays). Weed Sci. 36:764-769.

Begg, IE and NC. Turner. 1976. Crop water deficits. Adv. Agron. 28:161-217.

Bell, D.T. and DE. Koeppe. 1972. Noncompetitive effects of giant foxtail on the
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CHAPTER 2

GIANT FOXTAIL (Setariafaberi HERRM.) INTERFERENCE
IN NON-IRRIGATED CORN

ABSTRACT

Studies were conducted at East Lansing, MI in 1994 and 1995 to examine corn yield
response to giant foxtail [Setariafaberi (Herrm )] interference and to examine the effect of
giant foxtail density on giant foxtail biomass, seed production, and seed germination.
Treatments consisted of 0, 10, 30, 60, 84, and 98 giant foxtail plants per m of row in 1994
and 0, 10, 27, 30, 60, and 69 plants per m of row in 1995. The influence of giant foxtail
density on corn yield fit a hyperbola equation. Corn yields were reduced 13% in 1994 and
14% in 1995 fiom 10 giant foxtail plants per m of row. Com dry matter at maturity was
decreased 24 and 23% from 10 giant foxtail plants per m of row in 1994 and 1995,
respectively. Seed production increased linearly as inflorescence length increased. The length
of giant foxtail inflorescence increased as plant density increased and the number of
inflorescence produced per plant decreased Seed production ranged fiom 518 to 2544 seeds
per plant. Tm giant foxtail plants per m of row produced 157 00 seeds per m". Giant foxtail

seed germination was not affected by plant density. Nomenclature: giant foxtail, Setaria

41

 

42
faberi Herrm #‘ SETFA; corn, Zea mays L. # ZEAMX, ‘Pioneer 3573’. Additional index

words. Bioeconomic model, competition, Setaria, SETFA.

 

lLetters following this symbol are WSSA-approved computer code fiom Composite List
of Weeds, Weed Sci. 32, Suppl 2. Available from WSSA, 1508 W. University Ave.,
Champaign, IL 61821-3133.

43

INTRODUCTION

Giant foxtail is among the most widespread annual grasses in crop production in the
United States (18). Giant foxtail is not native to the United States and before 1930 there
were only isolated reports of its existence in the United States (9). The rapid infestation of
giant foxtail is attributed to its ability to adapt to several environments and its tremendous
reproductive capabilities (20).

Researchers have documented that giant foxtail germinated and emerged early in the
growing season and concluded the earlier giant foxtail emerged, the larger the growth of the
inflorescence (20). The date of emergence also affects the number of tillers produced per
plant and, subsequently, the number of inflorescence produced per plant as late germinating
giant foxtail plants produced fewer tillers (18). Increasing the number of inflorescence
produced per plant and the length of the inflorescence resulted in increased amounts of seed
produced per plant (20).

Weed escapes present a serious problem on Midwestern firms (13). Weeds reduced
crop yields primarily by competing for light, water, and nutrients (21). Interference fiom
giant foxtail reduces com yield and profit (13). The correct weed management decisions are
based on the relationship between weed density and corn yield loss.

The severity of yield losses due to interfering weeds is dependent upon the duration
of the weed competition (23). Gleason (7) noted that the longer giant foxtail plants were

present, the more crop yields were suppressed Giant foxtail reduced corn yield 63, 124, 315,

44

441, and 1133 kg ha'1 and soybean yield 0, 0, 63, 124, and 1133 kg ha'1 when removed at 7.5,
15, 22.5, and 30 cm in height and at maturity, respectively (11). In addition, total dry matter
remained constant whether the dry matter consisted of a weed-free crop or a crop and giant
foxtail biculture. Field studies by the same authors (9, 12) investigated the interference from
giant foxtail seeded 3, 6, 9, and 12 weeks after crop planting. Giant foxtail reduced corn and
soybean yield 13 and 27%, respectively, when seeded with the crop. Giant foxtail plants
seeded three weeks after the crop did not reduce corn or soybean yields. Interfering giant
foxtail plants reduced corn yield, cob weight, ear weight, stalk diameter, soil temperature, and
soybean yield and pod number (13). Corn and soybean yields, from 180 giant foxtail plants
per m of row, were reduced 25 and 28%, respectively. Giant foxtail plants did not affect corn
or soybean grain moisture content, crop height, or oil content of soybeans.

Harrison et al. (8) studied the interference and control of giant foxtail in soybeans and
reported every clump (3 to 6 plants) of giant foxtail plants per nine m of row reduced soybean
yield 0.8%. Ten giant foxtail plants per m of row reduced soybean yield 16%.

Langston and Harvey (15) reported 30 giant foxtail plants per m of row did not reduce
corn yields in 1993. However, the same density reduced corn yield 18% in 1994. Similarly,
Lambert ei al. (14) reported giant foxtail densities of 265 plants per m of row reduced corn
yield 20% in 1993 and 200 plants per m of row reduced corn yield 52% in 1994.

Researchers have documented the need for research on the biology of weeds (4). The
North Central Regional project NC-202 “Biological and Ecological Basis for Weed
Management Decision Support Systems to Reduce Herbicide Use” (1) is developing data sets
to quantify the interference of giant foxtail in the North Central region of the United States.

One objective of the project is to improve the accuracy and reliability of corn yield loss

45

estimations. Data will provide the framework for objective evaluation of costs and benefits
fiom weed control practices (1). These data will refine a bioeconomic model that will support
weed management decisions. The objectives of this research were: 1) to assess the yield and
dry matter loss in corn fiom giant foxtail interference in Michigan, 2) to estimate giant foxtail

seed production, and 3) to examine the effects of density on giant foxtail seed germination.

46

MATERIALS AND METHODS

Field Experiment. Experiments were conducted at the Michigan State University Agronomy
Research Farm in East Lansing, MI in 1994 and 1995. The soil was a Capac loam (fine -
loamy, mixed, mesic Aeric Ochraqualfs) with 3.5% organic matter and a pH of 7.1 in 1994
and 3.4% organic matter and a pH of 6.5 in 1995. The sites were fall moldboard plowed and
spring secondary tillage consisted of two diskings. Sites were fertilized according to soil
nutrient analysis. In 1994, 336 kg ha'1 6-24-24 and 305 kg ha'1 46-0-0 were applied broadcast
before spring disking. In 1995, 140 kg ha" 6-24-24 and 336 kg ha'1 46-0-0 were applied.
Corn ‘Pioneer 3573’ was planted May 10, 1994 and May 8, 1995 at 59280 seeds per ha in
7 6-cm-wide rows (Table 1). Com emergence was 11 and 10 days after planting (DAP) in
1994 and 1995, respectively. Giant foxtail emergarce was 2 days after the corn in both years.
The experimental design was a randomized complete block, and treatments were replicated
four times. Treatments consisted of 0, 10, 30, 60, 84, and 98 giant foxtail plants per m of row
in 1994 and 0, 10, 27, 30, 60, and 69 giant foxtail plants per m of row in 1995. Plots were
four rows wide and 10.5 m long in 1994 and 9.0 m long in 1995.

Metolachlor (2-chloro- N-(2-ethyl-6-methylphenyl)- N-(2-methoxy- l-methylethyl)
acetamide) at 2.2 kg ha'1 was applied in a 38-cm band between the corn rows, to the
experimental area, and bentazon (3-(1-methylethyl)-lH-2,1,3-benzothiadiazin-4(3H)-one 2,2-
dioxide) at 1.1 kg ha'1 was applied broadcast to control late emerging broadleaves in 1994

and 1995.

47

Natural infestations of giant foxtail were hand thinned to treatment densities 10 days
after emergence. Giant foxtail plants were spaced evenly along the com row and remained
in the field for the entire grong season. Plots were hand-weeded throughout the growing
season to remove weeds other than giant foxtail Corn density was recorded at maturity to
evaluate mortality.

All data were collected fiom plants in the inner two rows of each four-row plot. A
l-m section of row, in one of the two middle rows, was monitored and removed at corn
maturity to measure the following: corn grain, corn dry matter, and giant foxtail dry matter.

Giant foxtail seed production was calculated by hand-harvesting seed inflorescence
as they matured, measuring their length, and counting the seeds. Seed production estimates
were based on the number of inflorescence and the length of inflorescence produced per plant.
The number of seeds produced for a given inflorescence length was multiplied by the number
and the length of inflorescence to estimate the number of seeds produced per plant. The
number of giant foxtail plants per m of row was multiplied by 1.32 to convert plants per m
of row to plants m'z. The number of seeds produced per plant was multiplied by the number
of plants m’2 in each treatment to estimate the number of seeds m'z.

Plots were trimmed at corn maturity to 9.5 m and 8.0 m in 1994 and 1995,
respectively. Corn was mechanically harvested from the center two rows of each plot and
weights were adjusted to 15.5% moisture. Rainfall, growing degree days (GDD) and air
temperatures were recorded daily.

Seed Study. Giant foxtail inflorescence were collected on September 21, 1994 and 1995
fiom 1 m of row in each of the above mentioned plots. Seeds were hand removed, cleaned

and stored dry at room temperature. Studies were initiated approximately four months after

48

harvest. Lots of twenty-five seeds were placed on No. 2 Whatman filter paper in a 9 cm petri
dish and 8 ml of distilled water was added and the petri dishes were sealed. Seeds were
placed in growth chambers and exposed to 16 h of darkness at 20 C and 8 h of light (300 ,uE
in2 s") at 30 C. Seeds were considered germinated when the radicle exceeded 2 mm in
length. Gernrination was recorded 4, 7, and 14 days after light exposure. Studies consisted
of four replications and were repeated two times each year.

Data Analysis. Data were subjected to analysis of variance and means were separated by
least significant difference at the 0.05 level. When a variable significantly interacted with
years, a regression was performed separately for each year. When the interaction was not
significant, a regression was performed with the years combined.

The rectangular hyperbola model developed by Cousens (6) and the nonlinear
regression procedure of SAS (19) was used to relate corn yield loss to giant foxtail density
for the 1994 and the 1995 individually and in the pooled sample.

The relationship between inflorescence length and seed production was best described

by a linear equation. Seed production m’2 and giant foxtail density fit a quadratic equation.

49

RESULTS AND DISCUSSION

Experiment establishment dates for the two field studies were similar (Table 1). The
first rainfill (more than 0.5 cm) after corn planting was within 7 DAP in 1994 and 1995
(Table 2). Sufficient rainfall within the first four weeks of study establishment led to similar
emergence patterns in 1994 and 1995. Mid season environmental conditions were vastly
different. Twenty-eight cm of rain fell between 5 and 8 weeks after planting in 1994.
Conversely in 1995, 8 cm of rain fell in the same period (Table 2). However, cumulative
GDD in 1994 and 1995 from corn planting to silking (11 weeks after planting) were similar
(Table 2). Stand counts taken at maturity determined there was no corn mortality in either
1994 or 1995 (data not presented).
Corn Yield. Researchers have a wide range of models available for predicting crop yield loss
as a function of weed density. For low weed densities a linear regression may be used;
however, the selection of an equation should not be based solely on a high r2 value (16). A
quadratic equation will often give the highest 13 value but forces a maximum and eventual
decline on data that may be asymptotic (5). The rectangular hyperbola equation is considered
one of the most appropriate mathematical forms for relating crop yield loss to weed density.

The rectangular hyperbola equation provided a representative fit for the relationship
between com yield loss and giant foxtail density. This equation considers four parameters in
determining the predicted yield (5). The equation, Y = (WFY + D95*Z) [ 1- Ix/ (100(1 + 1x!

A))], employs the following variables and parameters:

50
Y = predicted yield
x = weed density
Z = “Dummy” (0/1) for years
WFY = weed-fiee yield
D95 = correction estimate for 1995 in pooled data
A = maximum percentage crop yield loss asymptote as x -> on

I = percentage loss for the first weed density unit

Weed-fiee yields ranged fiom 7590 kg ha'1 in 1994 to 12044 kg ha’1 in 1995 (Table
3). The asymptote (A) varied between 57% in 1994 and 28% in 1995. The I parameter
ranged fiom 1.8 to 2.4% between 1994 and 1995, respectively.

The hyperbolic equation predicted that initial giant foxtail densities contributed
similarly to corn yield reduction in 1994 and 1995 (Figure 1). T values indicate the I
parameter did not significantly differ from 0 in 1994 or the pooled data set. Our values are
generally higher, but are consistent with the literature. Com yield was reduced 13% in 1994
and 14% in 1995 fiom 10 giant foxtail plants per m of row. The predicted maximum
percentage corn yield reduction varied greatly between the two years with maximum yield
reduction two times greater in 1994. Statistically the A parameter was greater than 0 and less
than 100 at a 95% confidence level in 1994, 1995 and in the pooled data. This estimate
indicates that maximum yield loss fiom giant foxtail ranges fiom 28% in 1995 to 57% in
1994. Our results show higher reliability of the A parameter estimates than previous studies
(22).

Swinton et al. (22) evaluated various multi-species data sets to estimate weed

51

interference parameters in Michigan. Weed densities were regressed on crop yields using the
rectangular hyperbola equation and non-linear regression. Weed densities were based on
either stand counts or visual estimation in reduction in weed biomass compared to a weedy
check plot, along with actual weed densities for the weedy check plot. Because these trials
were repeated over years, it made it possible to evaluate the interaction of years with weed
competitiveness. Three model formulations were tested: a model in which the years had no
effect, a model in which year affects only the maximum reduction in weed-fiee yield, and a
model in which year affects both the weed-free yield and the competitiveness of weeds (22).
Maximum corn yield reduction from competing weeds (A) was estimated at 70% in these
data. It was then estimated that the first foxtail plant per ft2 (1) reduced corn yield 0.8 to
1.1%. Swinton et al. concluded that though the year significantly affects weed-free yields,
it does not interact significantly with weed-crop interference (22).

Similarly, Cardina et al. (4) studied the competitive effects of velvetleaf [Abuiilon
theophrasti (Medik.)] in conventional and no-tillage corn. Early emerging velvetleaf were
formd more competitive than late emerging velvetleaf The asymptote (A) ranged fiom 17%
in conventional tillage in 1992 to 69% in no-tillage in 1990. Similar to these data, seasonal
environmental variation in Michigan affected the maximum percent crop yield from giant
foxtail interference (asymptote).

Total Dry Matter. The dry matter of corn grain, corn stalks and cobs, and giant foxtail were
combined to obtain total dry matter production for each treatment (Table 4). In 1994 there
was no statistical difference in the total dry matter produced between treatments. Conversely,
in 1995 corn grown alone produced more total dry matter than corn grown in competition

with giant foxtail.

52

Ten giant foxtail plants per m of row, in the l-m subplot, decreased corn grain weight
31% and corn dry matter 24% when compared with the weed-fiee plots in 1994. These data
suggest the increase in giant foxtail dry matter compensates for the reduction in corn dry
matter and the total dry matter remains constant. Ten giant foxtail plants per m of row
decreased corn grain weight 13% and corn dry matter 23% in 1995. The total dry matter
produced in 1995 was higher when com was grown alone but in plots containing giant foxtail,
the production of total dry matter remained constant. This suggests the absence of giant
foxtail may enable corn to produce higher levels of total dry matter.

Studies have documented the reduction in corn dry matter is proportional to the
amount of resources giant foxtail utilizes (11, 13, 17). Researchers concluded that there is
a limited amount of resources available for plant growth and development (11, 17). These
same limited resources are required for corn and giant foxtail. Other researchers have noted
residues from mature giant foxtail plants contain allelopathic compounds that affect corn root
development and growth (3). Allelopathic compounds are water soluble and may have
leached through the root zone in 1994, but in the dry year of 1995, their presence may have
limited corn grth and total dry matter.

Seed Production. Giant foxtail plants growing without competition can produce more than
10000 seeds per plant (20). The maximum number of seeds produced per plant occurred at
10 plants per m of row. Maximum seed production was 2514 seeds per plant in 1994 and
2544 seeds per plant in 1995. The reduction in total seed production as compared with the
potential seed production is attributed to intraspecific and interspecific competition Corn not
only competes for similar soil nutrients as giant foxtail but also shades the existing giant

foxtail plants. Nutrients and light are both important environmental fictors in the

53

development of giant foxtail (10).

Researchers have noted a correlation between the number of giant foxtail seeds
produced and the inflorescence length (2, 20). Seed number per inflorescence, for giant
foxtail plants grown in Michigan, exhibited a linear relationship with inflorescence length
(Figure 2). However, the total number of seeds produced per plant decreased as giant foxtail
density increased.

Researchers have documented plant density and shading influences inflorescence
production. The total number of inflorescence produced per plant decreased as giant foxtail
density increased (18). Shade reduced the number of leaves, number of stems, and the
number of inflorescence produced per giant foxtail plant (10). In our research, inflorescence
length increased 21% in 1994 and 22% 1995 as giant foxtail density increased from the
minimum to maximum density (Table 5). However, the number of inflorescence produced
per plant decreased 78 and 76% in 1994 and 1995, respectively.

Total giant foxtail seed production, which was a function of the number of
inflorescence and the length of the inflorescence produced per plant, was estimated. The
relationship between giant foxtail density and seeds produced In2 best fits a quadratic
equation (Figure 3). This equation depicts an increase in seed production rn'2 with increased
giant foxtail density followed by a plateau, and subsequent decline in total seed production.
Cardina et al. (4) noted similar effects in velvetleaf seed production. The lowering of total
seed production at high density was associated with increased intraspecific competition.
Seed Study. Giant foxtail seed fiom densities greater than or equal to 30 plants per m of row
had greater germination 4 and 7 DAP in 1994 (Table 6). However, 14 DAP there was no

significant difference in seed germination. This could be explained by a gradient in dormancy

54

of the seeds produced by different inflorescence. Because giant foxtail plants grown at low
densities produce numerous inflorescence, the dormancy of the seeds fiom the various
inflorescence may be affected. Seed fiom the more mature inflorescence may have less initial
seed dormancy. Giant foxtail density did not affect seed germination in 1995. Overall
germination suggests giant foxtail density does not significantly affect seed germination.
Other researchers have shown giant foxtail seed color (20) and inflorescence length (2) does

not affect seed viability.

10.

11.

12.

13.

55

LITERATURE CITED

Anonymous. 1995. Biological and ecological basis for weed management decision
support systems to reduce herbicide use. NC202 Regional Research Project
Proposal.

Barbour, J .C., III., and F. Forcella. 1993. Predicting seed production by foxtails
(Setaria spp.) Proc. North Cent. Weed Sci. Soc. 48:100.

Bhowmik, RC. and JD. Doll 1982. Corn and soybean response to allelopathic
efl‘ects of weed and crop residue. Agron. J. 74:601-606.

Cardina, J., E. Regnier, and D. Sparrow. 1995. Velvetleaf (A butilon theophrasti)
competition and economic thresholds in conventional and no-tillage corn (Zea
mays). Weed Sci. 43281-87.

Cousens, R 1991. Aspects of the design and interpretation of competition
(interference) experiments. Weed Technol 5:664-673.

Cousens, R 1985. A simple model relating yield loss to weed density. Ann. Appl.
Biol 107:239-252.

Gleason, LS. 1958. Weed control in corn in the wet tropics. Proc. North Cent.
Weed Sci Soc. 13:54.

Harrison, S.K, L.M. Wax and CS. Williams. 1985. Interference and control of
giant foxtail (Setariafaberi) in soybeans (Glycine max). Weed Sci. 332203-208.

Knake, EL. 1977. Giant foxtail: the most serious annual grass weed in the
Midwest. Weeds Today. 9:19-20.

Knake, EL. 1972. Effect of shade on giant foxtail. Weed Sci. 20:588-592.

Knake, EL. and F .W. Slife. 1969. Effect of time of giant foxtail removal from
corn and soybeans. Weed Sci 17:281-283.

Knake, EL. and F .W. Slife. 1965. Giant foxtail seeded at various times in corn and
soybeans. Weeds. 132331-334.

Knake, EL. and F .W. Slife. 1962. Competition of Setaria faberii with corn and

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

56

soybeans. Weeds. 10226-29.

Lambert, W.J., T.T. Bauman, M.D. White, and RA. Vidal. 1994. Giant foxtail
(Setariafaberi) interference in corn (Zea mays). Proc. North Cent. Weed Sci. Soc.
49: 137- 138.

Langston, SJ. and RG. Harvey. 1994. Using alachlor impregnated on dry fertilizer
to create varying giant foxtail populations for corn competition studies. Proc.
North Cent. Weed Sci. Soc. 49:18.

Little TM. and F .J. Hill. 197 8. Agricultural Experimentation: Design and Analysis.
John Wiley & Sons, New York. 195-227 pp.

Moolani, M.K, E.L. Knake, and F.W. Slife. 1964. Competition of smooth
pigweed with corn and soybeans. Weeds. 12:126-128.

Santelmann, P.W., J.A. Meade, and RA. Peters. 1963. Growth and development
of yellow foxtail and giant foxtail. Weeds. 11:139-142.

SAS Institute, Inc. 1988. SAS/STAT User’s Guide: Release 6.03 Edition. Cary,
NC. SAS Inst, Inc., 675-712 pp.

Schreiber, M.M. 1965. Effect of date of planting and stage of cutting on seed
production of giant foxtail. Weeds. 13:60-62.

Staniforth, D.W. 1957 . Effects of annual grass weeds on the yield of corn. Agron.
J. 492551-555.

Swinton, S.M, J. Stems, KA. Renner, and J.J. Kells. 1994. Estimating weed-crop
interference parameters for weed management models. Michigan agricultural
experiment station, Michigan State University. Research Report 538

Young, F.L., D.L. Wyse, and RJ. Jones. 1982. Influence of quackgrass
(A gropyron repens) density and duration of interference on soybeans (Glycine
max). Weed Sci. 30:614-619.

57

Table 1. 1994 and 1995 experiment establishment dates and applications.

 

 

 

 

 

Year
Event 1994 1995
Date
Corn Planting May 10 May 8
Metolachor Application May 11 May 10
50% Corn Emergence May 21 May 18
50% Giant F oxtail Emergence May 23 May 20
Giant Foxtail Thinning June 1-3 May 30-31
Bentazon Application June 11 June 10

 

58

Table 2. Rainfall and cumulative growing degree days (base temperature 30/10 C: max
/min) data of the 1994 and 1995 grong season.

 

 

 

Weeks after planting 1994 1995
Rainfall GDD Rainfall GDD
cm cm
-1 1.8 ----- 0 6 -----
0 0 6 28 5 1 38
1 0.0 106 1.6 89
2 0.6 191 1.5 137
3 0.0 274 0.4 230
4 1.0 371 0.5 329
5 7.6 542 0.0 468
6 9.9 656 2.6 621
7 1.7 780 2.9 726
8 9.2 922 2.0 846
9 1.3 1050 3.1 1018
10 3.3 1207 2.6 1160
11 0.0 1332 0.1 1316
12 2.5 1428 4.3 1482
13 6.1 1514 0.7 1666
14 4.1 1632 6.4 1827
15 0.0 1766 0.0 1961

 

Total 49.7 34.4

59

Table 3. Corn yield reduction from giant foxtail density: Rectangular hyperbola regression
parameter estimates (and standard errors).

 

 

 

 

 

Estimate
Parameter 1994 1995 Pooled data
WFYal 7 590** 12044" 6978“
(520) (276) (426)
D95 ------------ 5499M
(413)
I 1.8 2.4 2.0
(1.3) (1.0) (1.5)
A 57* 28" 39‘”
(16.3) (3.5) (7.2)
Regression statistics
Calculated r 2 b 0.84 0.94 0.96

 

‘Weed-free yield in kg/ha.

b Calculated by 1- (number of observations - 1) residual mean square/ total sum square.
*= t value significant at the 0.05 level.

** = t value significant at the 0.01 level.

60

Table 4. Total dry matter as influenced by giant foxtail density.

 

 

 

 

 

 

 

 

 

Dry matter
Density Corn grain Corn stalk/ cob Giant foxtail Total
plants/ m row g/ m row
1994
0 636 1477 O 1477
10 440 1155 75 1255
30 404 1101 180 1280
60 425 1184 235 1409
84 384 1288 332 1620
98 399 1299 336 1635
LSD (0.05) 206 304 64 NS
1995
0 986 2287 O 2287
10 853 1651 95 1866
27 842 1641 184 1825
30 829 1512 206 1817
60 717 1680 198 1878
69 685 1380 316 1696
LSD (0.05) 131 238 115 214

 

 

61

Table 5. Giant foxtail seed production as influenced by density.

 

 

 

 

 

 

 

Inflorescence length Inflorescence Seed
Density cm ------------ no./ plant ------------
plants/ 111 row 1994
10 73 4.6 2514
30 85 2.3 1427
60 86 1.3 704
84 94 1.4 883
98 92 1.0 518
LSD (0.05) 16 0.6 619
1995
10 65 5.1 2544
27 69 2.6 1239
30 71 2.0 934
60 82 1.3 594
69 83 1.2 586

LSD (0.05) 16 0.7 594

 

Table 6. Giant foxtail cumulative seed germination as influenced by density.

62

 

Cumulative germination

 

days after exposure

 

 

 

 

 

 

 

 

Density 4 7 14
plants/ m row %

1994

10 23 45 64

30 34 51 62

60 36 56 62

84 37 54 60

98 40 54 64

LSD (0.05) 7 5 NS
1995

10 20 39 59

27 16 40 58

30 16 37 56

60 16 41 55

69 20 46 65

LSD (0.05) NS NS NS

 

63

80 1
e 1994
‘ o 1995
— 1994
so ‘ ------- 1995

Corn yield reduction (%)
.5
O

N
O

 

 

 

o I I f r I l I l I l

0 20 40 60 80 100
Giant foxtail density (plantslm of row)

Figure 1. Predicted corn yield reduction in 1994 and 1995 as influenced by giant foxtail
density. Equation parameters for these functions are given in Table 3.

 

64

 

 

2000 -
y = 6.68x
R2 = 0.76
1500 -
=5 e ’ . '.
.0 . . 1;.
S
C 0 O o
'a 1000 — e,
0)
Gt 0
U) o 0 e
.0 o
80 o
500 - 3'-
. o
0 0’
o
o T 1 I l I I l
0 50 100 150 200 250

Inflorescence length (mm)

Figure 2. Giant foxtail seed production as affected by inflorescence length.

65

120 -

 

 

E
g 100 -
d) 0
at
m 0
8 80 -
O.
c
o 60 -
3 e
3 40 - °
a . °
3 .
6 20 _ y = -0.007x2 + 1.5x
0’ R2 = 0.76
o I r I 1 I l I l I 1
o 20 40 60 80 100

Giant foxtail density (plants/m of row)

Figure 3. Giant foxtail seed production as influenced by density.

CHAPTER 3

DORMANCY, GERMINATION, EMERGENCE AND SURVIVAL
OF GIANT FOXTAE (Setariafaberi Herrm.)
AND FALL PAN ICUM (Panicum dichotomiflorum Michx.)

ABSTRACT

Studies were completed to determine giant foxtail [Setariafaberi (Herrm )] and fill
panicum [Panicum dichotomiflorum (Michx. )] germination, emergence, grth rate, and
survival. Freshly harvested giant foxtail and fall panicum seeds were dormant at harvest.
Giant foxtail seed dormancy was overcome by an accelerated after ripening treatment of 3
days at 50 C. Fall panicum seed dormancy was overcome by a dark imbibition at 35 C for 7
days. Giant foxtail seed germination exceeded 60% when exposed to either a constant or
alternating temperature. Fall panicum seed germination was less than 3% when exposed to
a constant temperature, but was greater than 94% when exposed to an alternating 14 C (9
h) 28 C (15 h) temperature regime. Maximum emergence for giant foxtail and fall panicum
was from seeds buried 1 cm and l to 2.5 cm, respectively. Giant foxtail seedling growth rate
was six times greater than that of fill panicum at each temperature regime. Giant foxtail seed
viability increased when seeds were buried for six months. However, fill panicum seed
viability was not affected by burial. Incorporation of this information into bioeconomic

models could result in accurate predictions of weed germination for effective weed

66

67

management strategies. Nomenclature: giant foxtail, Setariafaberi Herrm. #1 SETFA; fill
panicum, Panicum dichotomiflorum # PANDI. Additional index words. After-ripening,

dormancy, emergence, germination, seed burial, Setariafaberi, Panicum dichotomiflorum.

 

lLetters following this symbol are WSSA approved computer code fiom Composite List
of Weeds, Weed Sci 32, Suppl 2. Available fiom WSSA, 1508 W. University Ave.,
Champaign, IL 61821-3133.

68

INTRODUCTION

Giant foxtail and fill panicum are prolific weeds that compete in crop production and
produce thousands of viable seeds (10, 16). Ten giant foxtail plants per m of row reduced
soybean yield 16% in Illinois (5), while seven fill panicum plants per m of row reduced
soybean yield 15% in North Carolina (2). Field grown giant foxtail and fill panicum plants
can produce more than 10000 (9) and 500000 (15) seeds, respectively. Giant foxtail and fill
panicum escapes not only produce seeds that germinate the following year, but many seeds
remain dormant and viable for several years (12). Differences in giant foxtail and fill panicum
infestations in the field, may be due to difi‘erences in the maximum depth of emergence, seed
production, herbicide use, or a differential response to temperature and light.

Freshly harvested giant foxtail seeds were predominantly dormant (10) and
unresponsive to light (13). Primary giant foxtail seed dormancy diminished over time at room
temperature (14), and similar effects in a shorter time period could be achieved by exposing
seeds to higher temperatures. Taylorson and Brown (14) reported increased germination in
81% of the seed lots tested although accelerated after-ripening (AAR) at 50 C caused a
decline in germination of some species (14). Secondary seed dormancy in giant foxtail was
induced by exposing seed to temperatures greater than 30 C for an extended period, or to 60
C for 7 days (11).

Freshly harvested fill panicum seeds were typically dormant, but dormancy

diminished with time (3). Researchers reported maximum fill panicum germination after a

69

4 to 5 month after-ripenirrg period at 22 C (4). Fall panicum seeds require exposure to light
and temperatures greater than 25 C for 9 to 21 days to induce germination (3, 12, 15).
Dormancy was also overcome by exposing fill panicum seeds to high temperatures,
alternating temperatures, stratification, and mechanical or chemical scarification (12).

Field studies concluded the maximum depth for giant foxtail emergence was 10 cm,
but half the emerged giant foxtail seedlings originated from a depth of 1 cm or less in a no-
tillage system (7 ). The greatest emergence of fill panicum was fiom a 0.2 to 2.0 cm depth
(15), while in other research, the maximum emergence depth for buried fill panicum seed was
7 cm (1, 16).

Germination and growth of giant foxtail were temperature dependent (17).
Researchers estimated the minimum temperature to initiate giant foxtail germination was 10
C (6). Temperature affects plant biomass and the date of tiller initiation (8). Giant foxtail
plants produced the maximum amount of dry matter when exposed to an air temperature of
27 C (9).

Many fields in agricultural production systems are infested with giant foxtail and fill
panicum. The use of herbicides has often been associated with the development of specific
weed infestations. Researchers have documented, that in 6 hours, fill panicum and giant
foxtail metabolized 44 and 7%, respectively, of the 1‘C atrazine [2-chloro-4-(ethyl-amino)-6-
(isopropyl amino)-s-triazine] applied. We could not find and field or greenhouse studies
directly comparing the dormancy, germination, and growth of these two grass species under
similar environmental conditions. We were interested in whether differences in seed biology
could explain the differences in infestations between these two species.

The objectives of this research were: 1) to determine the optimal conditions to

7O

overcome giant foxtail and fall panicum seed dormancy, 2) to determine the effect of
temperature on giant foxtail and fill panicum seed germination and emergence, 3) to
determine the effect of planting depth on giant foxtail and fill panicum seed emergence, and

4) to quantify giant foxtail and fall panicum seed mortality.

71

MATERIALS AND METHODS

Seeds were collected in October of 1994 at the Michigan State University Agronomy
Research Farm in East Lansing, MI. The mature seeds were hand cleaned and stored dry in
sealed containers at room temperature.

Overcoming Seed Dormancy. A three-fictor fictorial experiment containing four replicates
was conducted three times to determine the optimal conditions to initiate giant foxtail and fill
panicum seed germination Twenty-five seed samples were placed in 15 by 45 mm glass vials
and sealed with screw caps. The sealed vials were held in an oven at 40 or 50 C (:L-2 C) for
3 to 14 days. Following the accelerated after ripening (AAR) period, the seeds were placed
in 20 by 100 mm petri dishes containing No. 2 Whatman filter paper. Eight m1 of distilled
water were added and the petri dishes were sealed. Following imbibition, seeds were placed
in the dark at 35 C for one week. Seeds were transferred to growth chambers and exposed
to an alternating 20 C (16 h) 30 C (8 h) or 20 C (10 h) 30 C (14 h) temperature regime.
Seeds were exposed to 300 ,uE - m’2 - s'1 of fluorescent and incandescent light during the 30
C period. Seeds were considered germinated when the radicle exceeded 2 mm in length.
Germination was recorded 14 days after light exposure.

Constant Temperature. A single factor petri dish experiment examined the germination of
giant foxtail and fill panicum seeds when erqrosed to a constant temperature of 20 or 30 C.
Pre-treated giant foxtail (3 days AAR 50 C) and fill panicum (3 days AAR 40 C, followed

by 7 days dark imbibition at 35 C) seeds were placed in growth chambers after following the

 

72

same procedures as the dormancy study. Seeds were exposed to 8 h light (300 ME - rn‘2 ' s")
and 16 h darkness. Germination was recorded 21 days after light exposure (DAE). The
experiment contained six replicates and was repeated twice.

A two-fictor fictorial experiment examined the efi‘ect of constant temperature (20 or
30 C) on giant foxtail and fill panicum seed emergence. Seeds were planted in a Capac loam
(fine-loamy, mixed, Mesic Aesic Ochraqualfs) with 1.8 % organic matter and a soil pH of 6. 1,
at depths of 0, 1, 2.5, 5, 7.5, and 10 cm Fifteen seeds were planted and emergence was
recorded 7, 14, and 21 days after planting (DAP) and plant dry weights recorded. Each
treatment was replicated four times and the experiment was repeated twice.
Alternating Temperature. Seed lots of twenty-five pre-treated giant foxtail and fill
panicum seeds, using the same procedures as the constant temperature study, were imbibed,
transferred to growth chambers, and exposed to three alternating temperature regimes. These
were: 1) 7 C (9.4 h) 20 C (14.6 h), 2) 13 C (8.7 h) 26 C (15.3 h), and 3) 14 C (9.0 h)
28 C (15.0 h). Growth chamber settings sirmrlated growing conditions for East Lansing, M1
on the 15th of May, June, and July. Seeds were exposed to 8.5, 10.4, and 9.9 h light (300
ME - m“2 - s") in the May, June, and July temperature regimes, respectively. Germination was
recorded 4, 7, 14, and 21 DAE. The study contained six replicates and was repeated twice.

Another experiment examined the effects of alternating temperatures on seed
emergence. Seeds were planted in the same soil at the same depths as in the above-mentioned
experiment. Procedures were identical to the constant temperature experiment. Treatments
were replicated four times and the experiment was repeated twice.
Seed Burial. Fifty giant foxtail and fifty fill panicum seeds were placed in separate 10 by 10

cm nylon bags. On October 16, 1994 the bags were buried horizontally at 0, 1, 2.5, 5, 10,

73

20 cm depth in two field locations. The first location was a sandy loam soil with 1.8%
organic matter and a soil pH of 6. 1. The second location was a sandy clay loam soil with
2.9% organic matter and a soil pH of 6.8%. On April 16, 1995, the bags were exhumed and
the seeds removed All seeds recovered from each bag were tested for germination by placing
the seeds in 20 by 100 mm petri dishes containing No. 2 Whatman filter paper and 8 ml of
distilled water was added and the petri dishes were sealed. The petri dishes were then placed
in growth chambers at 20 C (16 h) 30 C (8 h). Seeds were considered germinated when the
radicle exceeded 2 mm in length. Twenty-one DAE the petri dishes were opened and the
germinated seeds were removed. Ungerminated seeds were air dried for 7 days and imbibed
with 8 ml of distilled water and placed in the grth chambers for an additional 7 days. Seeds
were then visually examined to determine if they were nonviable seeds.

Data Analysis. Data were subjected to analysis of variance and in each experiment data is
presented separately for each grass species. Means were separated by least significant

difference at the 0.05 level.

 

If.

74

RESULTS AND DISCUSSION

Overcoming Seed Dormancy. Because both giant foxtail and fill panicum seeds have a
strong innate seed dormancy, some external conditioning was required before conducting
research on the germination and emergence of these species. Germination of giant foxtail and
fall panicum seeds were significantly increased by an AAR treatment, but in a contrasting
manner (Table 1). Giant foxtail seed germination was higher when exposed to the 50 C AAR
treatment whereas fill panicum seed germination decreased when exposed to the 50 C AAR
treatment. The length of AAR was also tested. Previous research noted a decline in
germination of giant foxtail when the seeds were exposed to an AAR treatment for greater
than 14 days at 50 C or greater than 3 days at 60 C (14). Exposing giant foxtail seeds to
three days or longer at either of the AAR temperatures significantly increased germination,
when compared with rmexposed seed that agrees with research by Taylorson and Brown (14).
There was no difference in the germination of fill panicum seeds for any of the AAR lengths
tested. Taylorson (12) reported an AAR treatment of 50 C was not sufficient to overcome
fall panicum seed dormancy completely, and seed required imbibition and exposure to
complete darkness to overcome dormancy. Our results in preliminary studies were similar
(data not reported).

Seeds of both species were exposed to two photoperiods (Table 2). Fall panicum
germination was not affected by either of the photoperiods tested, but giant foxtail

germination was decreased by the 20 C (10 h) 30 C (14 h) photoperiod. Our results support

‘r‘ r.'r

 

75

Alex (1) and others in that the optimum germination condition for fill panicum is either a 20
C (16 h) 30 C (8 h), or a 20 C (10 h) 30 C (14 h) temperature regime (13).

Constant Temperature. Giant foxtail germination decreased when exposed to a constant
30 C, when compared with 20 C (Table 3). Germination of giant foxtail at 20 C was similar
to results when the seeds were exposed to alternating temperatures for 21 days (Table 5).
Giant foxtail germination was independent of the type of temperature exposure (constant or
alternating), but dependent upon the maximum temperature with 30 C reducing germination.
Fall panicum germination was less than 3% when exposed to either 20 or 30 C. This supports
Taylorson’s (12) research in which fill panicum seeds required exposure to alternating
temperatures to initiate germination.

The effect of constant temperature on the emergence and individual plant dry weight
was also examined (Table 4). Giant foxtail emergence at a constant 20 or 30 C was similar.
However, plant dry weight at 20 C was less than plant dry weight at 30 C, and individual
plant dry weight decreased by 89% when grown at a constant 30 C when compared to an
alternating 14 C (9 h) 28 C (15 h) temperature regime (Table 6). Fall panicum emergence
was less than 6% when exposed to a constant temperature, and biomass accumulation by
plants emerging in the 30 C chambers was reduced 74% when compared with plants emerging
in the 14 C (9 h) 28 C (15 h) alternating temperature regime.

Alternating Temperature. Cumulative germination of giant foxtail seeds 14 and 21 DAE
were greatest when exposed to the June and July temperature regimes (Table 5). Fall
panicum seeds did not germinate in petri dishes when exposed to the May temperature
regime. Fall panicum weds grown in the June temperature regime required 7 days to initiate

gernrination whereas the July temperature regime required four days to initiate germination.

- ~" ;. $.fl7nw

 

w

76

There was less cumulative emergence of giant foxtail and fill panicum from the six
burial depths 7, 14, and 21 DAP when seeds were exposed to the May temperature regime
(Table 6). Although none of the fill panicum seeds germinated in petri dishes, 8% of the
seeds emerged when placed at the six burial depths in soil for 21 days and exposed to the May
temperature regime. This is attributed to soils buffering capabilities and the eventual
accumulation to a temperature that induces fill panicum seed germination. Although giant
foxtail and fill panicum cumulative germination was greater than 80% in petri dishes, June
exposed seeds cumulative emergence was less than 50% for both species. This is attributed
to little to no seeds emerging from greater than a 5 cm planting depth. One difference
between these species was that June exposed fill panicum seed emergence was greatest 14
and 21 DAP whereas giant foxtail germination in the June and July temperature regimes were
equivalent. Meaning that subtle changes in air temperature effects fill panicum emergence
more than giant foxtail

Temperature affected the accumulation of plant biomass by these species. Individual
giant foxtail and fill panicum plant dry weight were greater in the July than the June
temperature regime. Although June grown plants were exposed 20 minutes longer to the
maximum temperature (which was 2 C less than the July maxirmtm temperature), this was not
enough to offset the biomass accumulated in either giant foxtail or fill panicum Giant foxtail
plants, when grown under the same conditions, produced six times more individual plant
biomass compared with fill panicum. In contrast, Vengris (15) observed fill panicum
seedlings emerging between June 23 and July 7 were the most vigorous and fistest growing
plants in Massachusetts. These phenomena are intriguing because, as this researcher stated,

shading from a crop may reduce the light intensity reaching the soil surface by 70% which will

0 _ . ..'a'* .1 imF~L2£~Lm~w

 

77

reduce weed growth. The discrepancy in the grth rates between these data may be
explained by a differential rate in grth between giant foxtail and fill panicum when exposed
to low light intensities.

Emergence patterns between these species were similar (Table 7). The greatest
emergence of giant foxtail and fill panicum in the loam soil was fiom l and 1 to 2.5 cm
planting depth, respectively. Giant foxtail and fill panicum seedlings emerging fi'om the soil
surface to a 2.5 cm soil depth accumulated the greatest biomass. However, maximum
emergence of giant foxtail and fill panicum seeds was from a 7 .5 cm planting depth in this
loam soil. This could be explained by seedlings emerging from seeds buried 2.5 cm expend
less initial energy to develop roots because expanding roots are naturally wounded by soil.
Seed Burial. Seed recovery was 98% (i2%) for both grass species. Giant foxtail
germination decreased when seeds had remained on the soil surfice for 6 months but fill
panicrun did not (Table 8). Ungerminated seeds were visually examined and determined to
have lost viability. There was no difference in germination of either grass seed after burial in
1 to 20 cm in the soil for 6 months. Alex (I) conducted a similar seed burial study in
Branford, Ontario. He placed fill panicum seeds at the same five burial depths and reported
germination after 5 months burial fiom 73 to 91%, and concluded the average germination
increased with increased depth of burial. The lowering in germination in Alex’s study could
be accounted for in the increase in northern latitude.

Giant foxtail and fill panicum emergence patterns were similar but response to light
temperature, were different, as were species growth rates (Table 9). Fall panicum requires
an exposure to warm, alternating temperatures and light to initiate seed germination.

Implications of this in weed management are that early crop planting could reduce

78

competition fiom late emerging fill panicum Conversely giant foxtail germinated at lower
temperatures, and higher temperatures decreased germination. Delaying planting may reduce
the number of competing giant foxtail plants if spring soil temperatures exceed 30 C for an
extended period of time. Germination decreased by 25% for giant foxtail but only 7% for fall
panicum when on the soil surface. Implications are giant foxtail and fill panicum seed
germination will decrease if left on the soil surface for 6 months due to induced dormancy,
decay, predation, and reduced emergence fiom the soil surfice. Shallow seed burial (upper
1 cm of soil) may optimize emergence, and seed burial will increase giant foxtail seed survival.
Researchers increased understanding of weed seed biology my lead to accurate predictions
of weed emergence and the ability to develop preventive weed control strategies.
Incorporation of this information into bioeconomic models would more precisely predict the
time of emergence, the maximum depth in which each weed species can emerge, and the

percent of giant foxtail and fill panicum seeds that are not viable by the next growmg season.

10.

ll.

12.

79

LITERATURE CITED

Alex, J.F. 1980. Emergence from buried seed and germination of exhumed seed of fill
panicum Can. J. of Plant Sci. 60:635-642.

Ambrose, LG. and H.D. Coble. 1975. Fall panicum competition in soybeans.
Proc. South. Weed Sci. Soc. 28:36.

Baskin, J.M. and CC. Baskin. 1983. Seasonal changes in the germination responses
of fill panicum to temperature and light. Can. J. of Plant Sci 63:973-979.

Brecke, BJ. and W.B. Duke. 1980. Dormancy, germination, and emergence
characteristics of fill panicum (Panicum dichotomiflorum) seed. Weed Sci. 28:683-
685.

Harrison, S.K., L.M. Wax and CS. Williams. 1985. Interference and control of
giant foxtail (Setaria faberi) in soybeans (Glycine max). Weed Sci. 33:203-208.

Mester, TC. and DD. Buhler. 1991. Effects of soil temperature, seed depth, and
cyanazine on giant foxtail (Setaria faberi) and velvetleaf (A butilon theophrasti)
seedling development. Weed Sci 39:204-209.

Mester, TC. and DD. Buhler. 1986. Effects of tillage on the depth of giant foxtail
germination and population densities. Proc. North Cent. Weed Sci Soc. 41:4-5.

Michael, J.L., RS. Fawcett, and SE. Taylor. 1984. Effects of soil temperature on
early growth of giant foxtail (Setaria faberi) and velvetleaf (A butilon iheophrasti
Medic.) in soybeans. Abstr. Weed Sci Soc. Am 22:9.

Schreiber, M.M 1965. Development of giant foxtail under several temperatures and
photoperiods. Weeds. 13:40-43.

Schreiber, M.M. 1965. Effect of date of planting and stage of cutting on seed
production of giant foxtail. Weeds. 13:60-62.

Taylorson, RB. 1986. Water stress-induced germination of giant foxtail (Setaria
faberi) seeds. Weed Sci. 34:871-87 5.

Taylorson, RB. 1980. Aspects of seed dormancy in fill panicum (Panicum

13.

14.

15.

16.

17.

80

dichotomiflorum). Weed Sci 28:64-67.

Taylorson, RB. 1972. Phytochrome controlled changes in dormancy and germination
of buried weed seeds. Weed Sci. 20:417-422.

Taylorson, RB. and M.M. Brown. 1977. Accelerated after-ripening for overcoming
seed dormancy in grass weeds. Weed Sci. 25:473-476.

Vengris, J. 1975. Field growth habits of fill panicum Proc. Northeast Weed Sci. Soc.
29:8.

Vengris, J. and RA. Damon, Jr. 1976. Field growth of fill panicum and witchgrass.
Weed Sci 242205-208.

Wiese, AM. and L.K Binning. 1987. Calculating the threshold temperature of
development for weeds. Weed Sci. 35:177-179.

Fri

 

r ”“14““. . .~. -auuzm
1.

81

Table 1. Cumulative germination of giant foxtail and fill panicum seeds 0, 3, 7, and 14 days
after exposure to 40 or 50 C accelerated after-ripening.

 

Cumulative germination

 

 

 

 

 

 

 

 

 

 

40 C
Day after-ripening Giant foxtail Fall panicum
%
0 43 85
3 58 87
7 62 85
14 64 89
LSD (0.05)‘ 7 NS
50 C
Day after-ripening Giant foxtail Fall panicum
%
o 44 32
3 71 84
7 68 84
14 70 84
LSD (0.05)a 7 NS
LSD (0.05)b ** **

 

aSignificance between 4 times of after-ripening within each temperature.
bSignificance between 40 and 50 C accelerated after-ripening temperatures, when averaged
over 4 exposure periods.

.-.‘ sin-:31.

 

82

Table 2. Germination of giant foxtail and fill panicum seeds when exposed for 14 days to two
photoperiods.

 

Photoperiod
8 hrs light 14 hrs light
Species Germination LSD (0.05)
%
Giant foxtail 65 55 **
Fall panicum 85 85 NS

 

 

 

 

 

 

 

83

Table 3. Germination of giant foxtail and fall panicum seeds following 21 days at a constant
(20 or 30 C) temperature.

 

 

 

 

 

 

Giant foxtail Fall panicum
Temperature Germination
C %
20 77 2
30 6 1 1

LSD (0.05) ** NS

 

a)" ' JDB'

 

84

Table 4. Cumulative emergence and individual plant dry weight of giant foxtail and fill

 

 

 

 

 

 

 

panicum following exposure of seeds to 7, 14 and 21 days at a constant (20 or 30 C) 7“
temperature. '
Days after planting ’
7 14 21 .
E.
Giant foxtail Fall panicum
Temperature Emergence Dry wt. Emergence Dry wt

C ----- % ----- ug ----- % ----- us

20 21 23 23 0.5 0.7

30 24 24 25 1.6 0.6

LSD(0.05) NS NS NS **

NS

85

Table 5. Cumulative germination of giant foxtail and fall panicum seeds in petri dishes 4, 7,
14 and 21 days after exposure to three photoperiods.

 

Days after erqrosure

 

 

 

 

 

4 7 14 21 4 7 14 21
Giant foxtail Fall panicum
Temperature Cumulative germination
%

1" 60 65 65 70 0 0 0 0

2b 68 76 78 82 10 88 88 93

3c 68 69 72 81 85 90 92 95

LSD (0.05) NS 8 8 6 7 4 4 2

 

" Thirty year average for East Lansing, MI for May 15th.
b Thirty year average for East Lansing, MI for June 15th.
° Thirty year average for East Lansing, M] for July 15th.

 

86

Table 6. Cumulative emergence of giant foxtail and fill panicum seeds fiom 6 planting depths
7, 14 and 21 days after planting and individual plant dry weight when exposed to three
photoperiods.

 

 

 

 

 

 

Days after planting
7 14 21 7 14 21
Giant foxtail Fall panicum
Temperature Emergence Dry wt. Emergence Dry wt.
----- % us % H8
1’ 22 28 33 2.4 0 1 8 0.3
2b 30 43 44 7.9 16 41 50 1.6
3° 33 41 42 14.0 22 36 41 2.3
LSD (0.05) 5 6 6 2.6 3 3 3 0.3

 

° Thirty year average for East Lansing, M1 for May 15th.
b Thirty year average for East Lansing, MI for June 15th.
° Thirty year average for East Lansing, M1 for July 15th.

 

87

Table 7. Cunnrlative emergence of giant foxtail and fill panicum seeds buried at 0, l, 2.5, 5,
7.5, and 10 cm 7, 14 and 21 DAP and individual plant dry weight.

 

 

 

 

 

 

Days after planting
7 14 21 7 14 21
Giant foxtail Fall panicum
Depth Emergence Dry wt. Emergence Dry wt.

cm ----- % ----- pg ----- %---- #8
0.0 45 45 49 11.8 28 43 49 2.7
1.0 65 74 74 13.2 32 48 56 2.8
2.5 40 57 64 15.2 16 48 55 2.0
5.0 18 43 47 7.8 1 14 36 0.8
7.5 3 3 3 0.7 0 3 3 0.2

10.0 0 0 0 0.0 0 0 0 0
LSD (0.05) 11 8 8 3.6 5 4 5 0.5

 

 

88

Table 8. Germination of giant foxtail and fill panicum seeds buried six months at 0, 1, 2.5,
5, 10 and 20 cm soil depth and then exposed to 16 hrs 20 C, 8 hrs 30 C.

 

 

 

 

 

 

l
Germination
Depth Giant foxtail Fall panicum

cm %

0.0 75 98 ,
1.0 87 99

2. 5 88 100
5.0 90 99

10.0 96 99

20.0 95 99

LSD (0.05) 10 NS

 

89

Table 9. Characteristics of giant foxtail and fill panicum

 

 

 

Species

Characteristic Giant foxtail Fall panicum
Seed dormancy at harvest. Yes Yes
Requires light to induce germination.“ No Yes
Requires alternating temperature for germination. No Yes
Temperature affects germination. Yes Yes
Germination May temperature regime.b Yes No
Germination June temperature regime.c

4 DAE Yes No

7 DAE Yes Yes
Germination July temperature regime.d Yes Yes
Germination reduced after 6 mo on soil surfice. Yes No
Seed survival affected by burial depth.‘ No No
Optimal emergence depth. 1 cm 1- 2.5 cm
Percent emergence of seed from the soil surface. 49 49
Growth rate.f 14.0 pg 2.3 ug

 

 

‘ Preliminary results and Taylorson, 1980.

b Thirty year average for East Lansing, M1 for May 15th.

° Thirty year average for East Lansing, MI for June 15th.

‘ Thirty year average for East Lansing, MI for July 15th.

° Seed burial for 6 months.

I Individual plant dry weight 21 DAP when exposed to 14 C (9 h) 28 C (15 h) temperature

regime.

7‘ '-

 

ntcuran Stare UNIV. LIBRQRIES
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