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This is to certify that the
thesis entitled

EFFECT OF SHADE AND SOYBEAN (Glycine max) ROW
WIDTH AND PLANT POPULATION ON NIGHTSHADE
SPECIES (Solanum spp.).

presented by

Adrienne Marie Rich

—._--n--a-.-o-n-I-0-a-c-o-o-o-o-0-0-.-.-v

has been accepted towards fulfillment
of the requirements for the

MS. degree in Crop and Soil Sciences

MaTor Professor’s Signature
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( (7 /
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6/01 c1ClRC/DatoDuo.p65-p.15

EFFECT OF SHADE AND SOYBEAN [Glycine max (L.) Merr] ROW WIDTH
AND PLANT POPULATION 0N NIGHTSHADE SPECIES (Solanum spp.)
By

Adrienne Marie Rich

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
Department of Crop & Soil Sciences

2003

ABSTRACT

EFFECT OF SHADE AND SOYBEAN [Glycine max (L.) Merr] ROW WIDTH
AND PLANT POPULATION ON NIGHTSHADE SPECIES (Solanum spp.)

By

Adrienne Marie Rich
Nightshades (Solanum spp.) compete with soybean for moisture, nutrients, and light and
reduce crop yield and quality. Eastern black nightshade (Solanum ptycanthum) is
considered to be a shade tolerant weed, implying that emergence and grth may not be
affected beneath the soybean canopy, whereas, hairy nightshade (Solanum sarrachoides)
does not persist in dense shade. Studies were conducted in the field, growth chamber, and
greenhouse to determine the effects of shade, soybean row Spacing, and plant population
on nightshade growth and development. There was no difference in eastern black
nightshade emergence regardless of soybean row Spacing and population. One
application of glyphosate 30 days after planting when soybean was at the V3 stage
controlled eastern black nightshade that was 2.5 cm tall both years. Soybean planted in 19
cm rows at populations of 308 000, 432 000, and 556 000 seeds/ha reduced eastern black
nightshade growth and reproduction compared to soybean planted at 185 000 seeds/ha in
76 cm rows. Soybean yield was reduced by eastern black nightshade in the 76 cm rows
when planted at 432 000 seeds/ha. Eastern black and hairy nightshade growth and
reproduction were reduced when grown under reduced irradiances of 63 and 51
pE/mZ/sec. These results indicate that a 19 cm soybean row Spacing or increasing

soybean population will reduce the grth and reproduction of these shade tolerant

species.

ACKNOWLEDGMENTS

I would like to take this opportunity to extend an enormous thank you to Karen
Renner for making this degree possible, guiding my thoughts, and continuing to
challenge me these past two years. I would also like to thank Jim Kells for the
opportunity to teach his undergraduate weed science class.

I would like to thank my family for their support and especially my parents for
their assistance, love, and encouragement. I would like to thank my Grandma and
Grandpa Rich for instilling my love for agriculture. I would also like to thank Gary
Powell for all his technical assistance. And a special thanks to Trevor Dale, Aaron
Franssen, Eric Nelson, Brad Fronning, Amy Guza, Sarah Marshall, Corey Guza, Eric
Nelson, Scott Bollman, Ryan Robinson, and Terry Schulz for all of their assistance and

support through the various aspects of my graduate research career.

iii

TABLE OF CONTENTS

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

LIST OF FIGURES ........................................................................ ix

CHAPTER 1

REVIEW OF LITERATURE ........................................................... 1
INTRODUCTION ................................................................. 1
SOYBEAN ROW SPACING AND PLANT POPULATION. . . . . . . . ....1
USE OF GLYPHOSATE IN SOYBEANS .................................... 4
NIGHTSHADE EMERGENCE AND GROWTH ............................ 5
EFFECT OF SHADE ON PLANT GROWTH .............................. 14
LITERATURE CITED ......................................................... 16

CHAPTER 2

NARROW ROW SPACING INCREASED CONTROL OF EASTERN BLACK
NIGHTSHADE (Salanum ptycanthum) IN GLYPHOSATE- RESISTANT

SOYBEAN (Glycine max) IN MICHIGAN ......................................... 20
ABSTRACT ...................................................................... 20
INTRODUCTION ............................................................... 21
MATERIALS AND METHODS .............................................. 25

General Methods for Field Experiments ............................. 25
Eastern black nightshade emergence ........................ 26

Herbicide application .......................................... 26

Soybean canopy development ................................ 27

Eastern black nightshade biomass ........................... 28

Microplots ...................................................... 28

Soybean yield ................................................... 29

Statistical analysis .............................................. 29

RESULTS AND DISCUSSION ............................................... 30
Eastern black nightshade emergence ................................. 3O
Herbicide application ................................................... 31
Soybean canopy development ......................................... 32
Eastern black nightshade biomass .................................... 33
Microplots ................................................................ 35
Microplot yield .......................................................... 37
Soybean Yield ........................................................... 38
LITERATURE CITED .......................................................... 41

CHAPTER 3

THE INFLUENCE OF LIGHT QUANTITY AND QUALITY ON
THE EMERGENCE AND GROWTH OF EASTERN BLACK

iv

NIGHTSHADE (Solanum ptycanthum) AND HAIRY NIGHTSHADE

(Solanum sarrachoides). ................................................................. 5 8
ABSTRACT ........................................................................ 58
INTRODUCTION ................................................................. 59
MATERIALS AND METHODS ................................................ 62

The effect of neutral density shading on germination of eastern
black nightshade and hairy nightshade ................................. 62
The effect of light quality and quantity on the growth of eastern
black nightshade and hairy nightshade ................................. 63
RESULTS AND DISCUSSION ................................................. 65
The effect of neutral density shading on germination of eastern
black nightshade and hairy nightshade ................................. 65
The effect of light quality and quantity on the grth of eastern
black nightshade and hairy nightshade ................................. 66
Light quantity ..................................................... 66
Light quality ....................................................... 67
LITERATURE CITED ............................................................ 75
APPENDICES .............................................................................. 77
CHAPTER 2 AN OVA TABLES ................................................. 77
CHAPTER 3 ANOVA TABLES ................................................ 93

LIST OF TABLES

CHAPTER 2

NARROW ROW SPACING INCREASED CONTROL OF EASTERN BLACK
NIGHTSHADE (Solanum ptycanthum) IN GLYPHOSATE- RESISTANT
SOYBEAN (Glycine max) IN MICHIGAN

Table 1. Monthly precipitation recorded at the Michigan State University
Department of Horticulture Teaching and Research Center, East Lansing, MI,

and at the Clarksville Horticultural Experiment Station at Clarksville,

MI ............................................................................................. 46

Table 2. Eastern black nightshade density and dry weight per plant in October
2001 at East Lansing as affected by soybean row spacing and plant
population .................................................................................... 47

Table 3. Density of eastern black nightshade in October 2002 at Clarksville and
East Lansing as affected by soybean row spacing and plant population ............ 48

Table 4a. Eastern black nightshade density in microplots at East Lansing in
2002 ........................................................................................... 49

Table 4b. Eastern black nightshade density in microplots at Clarksville in
2002 ........................................................................................................................ 50

Table 5. 2002 eastern black nightshade dry weight per plant in microplots as
affected by soybean row spacings of 19- and 76-cm ................................. 51

Table 6. 2002 eastern black nightshade berry dry weight in microplots as
affected by soybean row spacings of 19- and 76-cm ................................... 52

Table 7a. Effect of soybean row spacing, plant population, and eastern black
nightshade on microplot soybean yield at East Lansing in 2002. . . . . . ......53

Table 7b. Effect of soybean row spacing, plant population, and eastern black
nightshade on microplot soybean yield at Clarksville in 2002 ........................ 54

Table 8. Effect of soybean row spacing, population, and herbicide treatment on
soybean yields at East Lansing in 2001 ................................................... 55

Table 9a. Effect of soybean row Spacing, population, and herbicide treatment on
soybean main plot yield at East Lansing in 2002 ....................................... 56

vi

Table 9b. Effect of soybean row spacing, population, and herbicide treatment on
soybean main plot yield at Clarksville in 2002 .......................................... 57

CHAPTER 3

THE INFLUENCE OF LIGHT QUANTITY AND QUALITY ON THE
EMERGENCE AND GROWTH OF EASTERN BLACK NIGHTSHADE (Solanum
ptycanthum) AND HAIRY NIGHTSHADE (Solanum sarrachoides)

Table 1. Effect of neutral shading on the cumulative emergence of eastern black
nightshade and hairy nightshade .......................................................... 71

Table 2. Effects of neutral shading on the reproductive, stem, leaf, and total dry weights,
leaf area, and specific leaf area of eastern black nightshade and hairy
nightshade .................................................................................... 72

Table 3. Comparison of radiation quality on the reproductive, leaf, total dry
weights, leaf area, and specific leaf area of eastern black nightshade and hairy
nightshade .................................................................................... 73

CHAPTER TWO APPENDIX

NARROW ROW SPACING INCREASED CONTROL OF EASTERN BLACK
NIGHTSHADE (Solanum ptycanthum) IN GLYPHOSATE- RESISTANT
SOYBEAN (Glycine max) IN MICHIGAN

Table 2. Eastern black nightshade density and dry weight per plant in October
2001 at East Lansing as affected by soybean row spacing and plant
population .................................................................................... 84

Table 3. Density of eastern black nightshade in October 2002 at Clarksville and
East Lansing as affected by soybean row spacing and plant population ............ 84

Table 4a. Eastern black nightshade density in microplots at East Lansing in
2002 ........................................................................................... 85

Table 4b. Eastern black nightshade density in microplots at Clarksville in
2002 ........................................................................................................................ 86

Table 5. 2002 eastern black nightshade dry weight per plant in microplots as
affected by soybean row spacings of 19- and 76-cm ................................. 87

Table 6. 2002 eastern black nightshade berry dry weight in microplots as
affected by soybean row spacings of 19- and 76-cm ................................... 89

Table 7a. Effect of soybean row spacing, plant population, and eastern black
nightshade on microplot soybean yield at East Lansing in 2002 ..................... 90

vii

Table 7b. Effect of soybean row spacing, plant population, and eastern black

nightshade on microplot soybean yield at Clarksville in 2002 ....................... 90
Table 8. Effect of soybean row spacing, population, and herbicide treatment on
soybean yields at East Lansing in 2001 .................................................. 91
Table 9a. Effect of soybean row spacing, population, and herbicide treatment on
soybean main plot yield at East Lansing in 2002 ....................................... 91
Table 9b. Effect of soybean row spacing, population, and herbicide treatment on
soybean main plot yield at Clarksville in 2002 .......................................... 92
CHAPTER THREE APPENDIX

THE INFLUENCE OF LIGHT QUANTITY AND QUALITY ON THE
EMERGENCE AND GROWTH OF EASTERN BLACK NIGHTSHADE (Solanum
prycanthum) AND HAIRY NIGHTSHADE (Solanum sarrachoides)

Table 1. Effect of neutral shading on the cumulative emergence of eastern black
nightshade and hairy nightshade .......................................................... 93

Table 2. Effects of neutral shading on the reproductive, stem, leaf, and total dry weights,
leaf area, and specific leaf area of eastern black nightshade and hairy
nightshade .................................................................................... 93

Table 3. Comparison of radiation quality on the reproductive, leaf, total dry
weights, leaf area, and specific leaf area of eastern black nightshade and hairy
nightshade .................................................................................... 95

viii

LIST OF FIGURES

CHAPTER 2

NARROW ROW SPACING INCREASED CONTROL OF EASTERN BLACK
NIGHTSHADE (Solanum ptycanthum) IN GLYPHOSATE- RESISTANT
SOYBEAN (Glycine max) IN MICHIGAN

Figure 1. Cumulative eastern black nightshade emergence at East Lansing, MI

in 2001 ....................................................................................... 43
Figure 2a. Cumulative eastern black nightshade emergence at East Lansing, MI

in 2002 ........................................................................................ 43
Figure 2b. Cumulative eastern black nightshade emergence at Clarksville, MI

in 2002 ....................................................................................... 44
Figure 3. Soybean canopy development at East Lansing in 2001 ..................... 44
Figure 4a. Soybean canopy development at East Lansing in 2002 ................... 45
Figure 4b. Soybean canopy development at Clarksville in 2002 ..................... 45
CHAPTER 3

THE INFLUENCE OF LIGHT QUANTITY AND QUALITY ON THE
EMERGENCE AND GROWTH OF EASTERN BLACK NIGHTSHADE (Solanum
plycanthum) AND HAIRY N IGHTSHADE (Solanum sarrachoides)

Figure 1. Temperature differences in the greenhouse due to Shade treatment... . ...74
CHAPTER TWO APPENDICES

NARROW ROW SPACING INCREASED CONTROL OF EASTERN BLACK
NIGHTSHADE (Solanum ptycanthum) IN GLYPHOSATE- RESISTANT
SOYBEAN (Glycine max) IN MICHIGAN

Figure 1. Cumulative eastern black nightshade emergence at East Lansing, MI

in 2001 ....................................................................................... 77
Figure 2a. Cumulative eastern black nightshade emergence at East Lansing, MI

in 2002 ........................................................................................ 77
Figure 2b. Cumulative eastern black nightshade emergence at Clarksville, MI

in 2002 ....................................................................................... 77
Figure 3. Soybean canopy development at East Lansing in 2001 ..................... 78

ix

Figure 4a. Soybean canopy development at East Lansing in 2002 ................... 80

Figure 4b. Soybean canopy development at Clarksville in 2002 ..................... 82

CHAPTER 1

REVIEW OF LITERATURE

INTRODUCTION

Weed interference can reduce soybean plant dry weight and seed yield (Légere
and Schreiber 1989). A common1ambsquarters(Chenopodium album L.) density of 32
plants per 10 m of soybean row reduced soybean yields by 20% when common
lambsquarters were present all season (Crook and Renner 1987). Soybean yield was
reduced 46 to 52% and 85 to 92% by densities of 3 and 18 giant ragweed (Ambrosia
trz'fida L.) per 10 m of row, respectively (Baysinger and Sims 1991). Coble et al. (1981)
found that as few as four common ragweed (Ambrosia artemiiszfolia L.) plants per 10 m
of row reduced soybean yields. Full season interference from 4 common cocklebur
(Xanthium strumarium L.) per 10 m of row reduced soybean yields by an average of 13%
(Bloomberg et al. 1982). In these studies, soybean was planted in 76- or 90-cm rows with
plant populations of 335 000 to 450 800 seeds per hectare. Eastern black nightshade
(Solanum ptycanthum) densities of 2 plants per m2 did not reduce soybean yield,
indicating that eastern black nightshade is not a strong competitor with soybean (Crotser

and Witt, 2000).

SOYBEAN ROW SPACING AND PLANT POPULATION
Soybean planted in narrow rows, usually less than or equal to 25 cm, have greater
yield potential than soybean planted in wide rows. Ethredge et al.. (1989), reported that

soybean yield increased as row spacing decreased from 7 6-, to 51-, to 25-cm when

averaged over two soybean cultivars and three plant populations. In a study conducted by
Etheredge et al.. (1989), the number of soybean plants producing seed at harvest was
compared to the initial plant population. Soybean seed was planted in 25-, 51-, and 76-
cm rows using a cone push planter. Seeds were over planted and thinned to desired
populations of 260 200, 390 400, and 520 400 seeds per hectare within two weeks after
emergence. When compared across all populations, the number of plants producing seed
in the 76—cm rows was only 77% of the initial plant population; whereas, the number of
plants producing seeds in the 51- and 25-cm rows was 93 and 97%, respectively. This
response was probably due to the more uniform plant distribution in the narrow rows
which resulted in less interplant competition during the vegetative stages. The yield
increase of narrow row soybean can be attributed to the development of a canopy that
provides complete ground cover before the time that pod-fill occurs. Full ground
canopies intercept more solar radiation and have greater photosynthesis than do partial
ground cover canopies (Shibles and Weber 1966). With the same leaf area index in
narrow and wide rows, there was greater light interception in narrow rows because of a
more uniform leaf distribution, which resulted in higher yield (Taylor et al.. 1982).

In contrast, Taylor (1980) reported that in years where water was limiting, row
Spacing had no effect on soybean yield. Soybean were planted in 25-, 50-, 75-, and 100-
cm rows at a plant population of 395 000 plants per ha. The increased interception of
solar radiation caused by the more even distribution of plants growing in narrow rows
resulted in greater water use during the early growing season and less moisture available

during pod fill.

Prior to the 1980’s, most soybean were planted in wide rows (76 to 104 cm) to
allow for the cultivation of weeds. There was no practical advantage of planting soybean
in narrow rows because sufficient weed control could not be obtained without cultivation.
The narrow choice of herbicides usually did not control all the weed species present so
one or two cultivations were necessary to control weeds which were not susceptible to a
herbicide. However, if weeds could be controlled early in the growing season, greater
season long weed control would be achieved in narrow rows due to faster canopy closure,
which would suppress late emerging weeds. Patterson et al.. (1988) reported decreased
weed yields in narrow row compared to wide row treatments. Mickelson and Renner
(1997) found 30% less weed biomass in narrow rows compared to wide row soybean
following postemergence herbicide treatments. Plant populations were 469 500 seeds per
ha in 19 cm row spacing and 358 000 seeds per ha in the 76 cm row spacing. Redroot
pigweed total leaf area was less in narrow row soybean than in wide row soybean with a
soybean population of 385 500 seeds per hectare (Légére and Schreiber 1989). Burnside
and Colville (1964) compared soybean row spacings of 25, 50, 75, and 100 cm at a
soybean seeding rate of 101 kg/ha, and found that the ground was completely shaded in
36, 47, 58, and 67 days, respectively. Weed control from chlorarnben treatments was
more effective as row spacing decreased. Soybean yields increased as row Spacing

decreased with soybean in 25 cm rows yielding 39% more than soybean in 100 cm rows.

USE OF GLYPHOSATE IN SOYBEAN
With the introduction of glyphosate for controlling summer annual weeds in

glyphosate resistant soybean, growers had a new option for weed management (Delannay

et al.. 1995). Glyphosate controls a broad spectrum of grass and broadleaf weeds, but
does not have soil residual activity, which allows weeds to emerge alter the herbicide
application if light and moisture are available. Ateh and Harvey (1999) reported that
glyphosate at 310 g ae/ha controlled giant foxtail (Setariafaberi Hernn.), common
lambsquarters, and velvetleaf (Abutilon theophrasti L.) if applied when the weeds were
small (<15 cm) and the soybean were at the V2 growth stage. When glyphosate was
applied to larger weeds (>15 cm), weeds were consistently controlled in narrow rows
only. This was attributed to early canopy closure and shading that reduced subsequent
weed emergence. It was noted, however, that for control of larger weeds, it was necessary
to use the recommended rate of 810 g ae/ha of glyphosate. Applying glyphosate +
imazethapyr, which has soil residual activity, at the V4 stage of soybean did not improve
weed control compared to glyphosate alone. Glyphosate alone provided adequate weed
control under the conditions of this study.

Producers may postpone application of glyphosate to improve late season weed
control. However, delaying the glyphosate application may increase the risk of soybean
yield loss due to weed competition and a late application timing may reduce the herbicide
efficacy on certain weed species (Gonzini et al.. 1999). Sequential applications of
glyphosate may increase overall weed control and reduce the risk of yield reductions due
to weed competition. Properly timed sequential applications could eliminate weeds
before weed competition occurs and could control later emerging weeds. However, by
planting soybean in narrow rows, the need for sequential applications of glyphosate to
control late emerging weeds may be eliminated. Young et a1. (2001) reported that

increasing the glyphosate rate or delaying the glyphosate application did not consistently

increase weed control or soybean yield. Glyphosate treatments usually resulted in greater
weed control and soybean yield than the standard herbicide treatments; however
glyphosate yielded less than the hand-weeded control in some site years, indicating that
weed control with glyphosate treatments applied mid-postemergence, late-postemergence
and sequential timings was not always sufficient to eliminate weed competition in
southern Illinois. Weed control by a single application of glyphosate was improved by the

use of 19- or 38- cm rows compared to 76-cm rows, regardless of plant population.

NIGHTSHADE EMERGENCE AND GROWTH

Eastern black nightshade has been a weed problem in soybean fields in the United
States for many years (Stoller and Myers 1989a). Eastern black nightshade interferes with
harvest and reduces crop quality because the juice fiom ruptured benies stains the
soybean seeds (Quackenbush and Anderson 1984a). Furthermore, nightshade berries are
often crushed during harvest, causing the weed seed to cling to the soybean seed which
can facilitate the spread of the weed to new areas or act as an initiation site for molds
during seed storage. The berries can also pass through combine screens and become a
contaminant that is very difficult to separate (Thompson and Witt 1987). Hairy
nightshade (Solanum sarrachoides) is a weed problem in dry beans (Phaseolus vulgaris
L.), with dense infestations reducing yield by as much as 77% in Alberta, Canada
(Blackshaw 1991). As few as 2 hairy nightshade plants per m significantly reduced dry
bean yields. Hairy nightshade is also a weed problem in both transplanted and direct
seeded tomato (Lycopersicon esculentum Mill.). Photosynthetic rates of both seeded and

transplanted tomatoes were reduced by at least 75% by 16 nightshade plants per m

compared to the weed free plots. Tomato yield was reduced by 45% in transplanted and
95% in seeded tomatoes by 20 hairy nightshade plants per m (Weaver et al.. 1987).

Shade effectively inhibits the growth of many weeds. The principle characteristic
of eastern black nightshade that enables it to be problematic in soybean fields is it’s
ability to grow in the shaded environment that exists beneath the soybean canopy. Stoller
and Myers (1989b), found that eastern black nightshade was able to grow beneath the
soybean canopy where irradiance levels were less than 100 uE/ m2 / 5, whereas,
velvetleaf, common lambsquarters, and tumble pigweed (Amaranthus blitoides L.) could
not. Eastern black nightshade adapted to low light intensities beneath the soybean canopy
by lowering respiration rate, root-to-shoot ratio, and leaf density, and increasing light
absorption efficiency (Stoller and Myers 1989a). Yield of dry beans infested with hairy
nightshade was likely affected by competition for light between the two species
(Blackshaw et a1. 1991). Hairy nightshade was taller than the dry beans for most of the
growing season, enabling it to exert a strong shading effect and reduce photosynthetic
active radiation (PAR) incidence on the dry beans for the latter part of the growing
season (Blackshaw et a1., 1991).

The problems associated with eastern black nightshade can be diminished by
increasing the competition from soybean plants. Quackenbush and Anderson (1984a),
working in Minnesota, reported that eastern black nightshade growth and berry
production were greatly reduced once the soybean canopy began to close. The primary
reason for this was attributed to the reduction in irradiance due to Shading by soybean
leaves. It was also noted that if there was a decrease in soybean competition due to

defoliation, as might occur with hail or disease, there was an increase in eastern black

nightshade growth and berry production. They also reported that in order to assure that

eastern black nightshade would not become a problem in soybean, even in instances of
bail or disease, control of eastern black nightshade may be required until early August.

The ability of eastern black nightshade to survive beneath a soybean canopy creates the
potential to become problematic long after other weeds have been forgotten.

Black nightshade (Solanum nigrum L.) generally has a reputation of being a late-
emerging species, and several authors have noted its ability to continue emerging
throughout the summer. This indicates that control of seedlings would be needed through
July and August (Rogers and Ogg 1989). Generally, eastern black nightshade emerges in
the spring when the daily maximum air temperature approaches 20°C (Ogg and Dawson
1984, Roberts and Lockett 1978). Ogg and Dawson (1984), working in Washington,
found there were significant differences in the patterns of emergence between eastern
black nightshade and hairy nightshade. Most of the eastern black nightshade seedlings
emerged within a two month period in the spring, whereas, seedlings of hairy nightshade
had several peaks in emergence from late April through late July and continued to emerge
throughout the growing season. Quackenbush and Anderson (1984b) found similar
results in Minnesota. These results may indicate that eastern black nightshade is not a late
emerging weed as previously suggested. Roberts and Lockett (1978) working in England,
reported that hairy nightshade emergence peaked in May or June, declined in July and
August, and ceased in September. Cultivation of the soil increased emergence and could
cause a second peak of emergence in July. Moist weather conditions also increased the
number of germination flushes. Ninety percent of eastern black nightshade emerged in

April and almost none afier June in Washington and Minnesota (Ogg and Dawson 1984,

Quackenbush and Anderson 1984b). Weed seed placement below 2.5 cm significantly
reduced germination of black nightshade (Solanum nigrum) regardless of soil type
(Vandeventer et al.. 1982).

Nightshade seeds became viable within a few weeks after anthesis. Eastern black
nightshadeseeds became viable 2 to 4 weeks after anthesis, with 30% germination after 4
weeks, 80% germination after 6 weeks, and 91% germination after 8 weeks (Thomson
and Witt 1987). Quackenbush and Anderson (1984b) found similar results for eastern
black nightshade, but found that five weeks were required after anthesis before hairy
nightshade seeds were viable. Shade during the grth and production of eastern black
nightshade increased the time required for seeds to become viable by about 50% if the
berries were dried before seed removal. Shade did not affect the time for seeds to become
viable if seeds were removed from fresh berries (Stoller and Myers 1989b).

Freshly harvested hairy nightshade seeds subjected to diurnally fluctuating
temperatures of 20 to 35°C failed to germinate. Hairy nightshade seed stored for several
months in dry, warm conditions, or moist conditions at 4°C, or buried in the field over
winter, developed the capability for germination at constant 25 or 30°C and at alternating
temperatures (Roberts and Boddrell 1983).

Generally, black nightshade seeds will not germinate at temperatures below 20°C
or above 40°C (Givelberg and Horowitz 1984, Roberts and Lockett 1978). Keely and
Thullen (1983) found that black nightshade seeds produced late in the season required
higher temperatures for optimum germination than did seeds produced early in the
growing season. Germination in light of dry-stored seeds of eastern black nightshade was

maximum at constant 30°C or at alternating 20/30°C (Thomson and Witt 1987). In the

dark, eastern black nightshade seeds germinated poorly over all temperature regimes
except alternating temperatures of 10/3 0°C and 20/30°C where 58% and 61%,
respectively, of the seeds germinated. Bugert and Burnside (1972) reported that hairy and
eastern black nightshade seeds germinated in the field when soil temperatures were
between 20° and 46° C. The optimum temperature for germination of both species was
30°C.

Ni ghtshades begin to emerge in the early spring and flowers appear 7 to 9 weeks
later (Keely and Thullen 1983). Eastern black nightshade grown without soybean
competition began to flower 1 to 3 weeks after reaching the 5 leaf- stage and in some
cases within six weeks afier seeds were planted (Quackenbush and Anderson 1984a).
Black nightshade growing without crop interference and planted April 1 through July 1
produced an average of 1000 berries per plant, whereas plants from seeds planted March
1, August 1, and September 1 produced 410, 620, and 30 berries, respectively, per plant
(Keely and Thullen 1983). Eastern black nightshade plants grown without intra- or
interspecific interference produced in 20 weeks 240 g dry weight and 5,960 berries per
plant. Conversely, plants grown under similar conditions but under 94% shade, produced
only 3 g dry weight and 23 berries per plant (Stoller and Myers 19893).

Eastern black nightshade that emerged with soybean and grew in the open spaces
between rows 75 cm apart produced 43 g dry weight and 264 berries per plant, whereas,
nightshades that grew between rows spaced 33 cm apart produced an average of less than
1 g dry weight and less than 1 berry per plant. Berry production declined under shade
because flowers were aborted (Stoller and Myers 1989b). It is important to note that even

the smallest eastern black nightshade plants produced some reproductive growth by the

last harvest date, contributing seeds to the soil bank for future infestations. The threshold
to prevent berry production was about 94% shade, a level commonly found beneath
soybean canopies during the middle of the growing season (Quackenbush and Anderson
1984a). In mid-July in Minnesota, less than 5% of the photosynthetically active radiation
(PAR) of full sun reached the ground between narrow spaced (18 cm) rows of soybean
planted at 10 seeds per m of row, whereas, 76% of full sun PAR reached the ground
between wide spaced (76 cm) rows of soybean planted at 30 seeds per m of row
(Quackenbush and Anderson 1984a). Eastern black nightshade planted in May with
soybean in narrow rows (18 cm) produced 50% fewer berries than did plants in soybean
in wide (76 cm) rows. Stoller and Myers (1989b) noted that a large proportion of the
berries were produced late in the season after soybean leaf abscission regardless of the
plants’ positions relative to the soybean row, emergence dates, or row width. They
attributed the large production of berries to the plants response to increased irradiance
that was experienced during this short period. Berry production of eastern black
nightshade and hairy nightshade is also enhanced in the fall because the nightshade is not
killed by light frosts and plants continue to produce berries after crop senescence (Stoller
and Myers 1989b). Quackenbush and Anderson (1984b) reported that eastern black
nightshade was more frost tolerant than hairy nightshade.

Eastern black nightshade is a prolific seed producer with 50 to 110 seeds per berry
(Rogers and Ogg 1989). Hairy nightshade berries contain 10 to 35 seeds per berry. Keely
and Thullen (1983) reported that an S. nigrum plant can produce over 30,000 seeds in a
season. Once the soil seed bank includes seeds from these Solanum species, these weeds

have the potential to infest the site for a number of years. Toole and Brown (1946),

10

working in England with plants identified as S. nigrum, showed that black nightshade
seeds in clay pots filled with soil and buried outdoors retained viability after 39 years. In
contrast, Bassett and Munro (1985), working with hairy nightshade and eastern black
nightshade, reported that 90% of the nightshade seed tested for longevity in soil was
viable for 5 years after collection and then the viability percentage dropped successively
to 73, 27, and 2% over the next 3 years. Roberts and Lockett (1978) found about 11% of
black nightshade seeds in cultivated soil were viable after 5 yr. Ni ghtshades can only
reproduce via seed so it is important to understand factors such as seed longevity,
germination, and emergence, as well as seed production when formulating control
measures of these weed Species.

Nightshades are not strong competitors against soybean (Quackenbush and
Anderson, 1984a). In competition with soybean, eastern black nightshade emergence and
survival was greatly reduced once the soybean canopy began to close. Of the 72 plots
having nightshade seeds planted into wide- or narrow-row soybean after mid-July, only 3
contained a nightshade plant by soybean harvest time. Eastern black nightshade that was
grown without soybean interference was able to complete its life cycle in ten weeks or
less. Thirty-three to 47% of the total dry weight was allocated to berry production. These
nightshade plants produced over 700 berries per plant and 800,000 seeds. In contrast,
those planted with soybean produced less than 60 benies and only 2500 seeds per plant.
Those nightshades that were planted 3 weeks or more after soybean produced 10 or fewer
berries (Quackenbush and Anderson 1984a). Stoller and Myers (1989a) found that
eastern black nightshade growth was closely associated with the total irradiance received

by the plants. Shade structures were constructed in the field with saran mesh cloth rated

11

for the amount of solar radiation intercepted. Shoot growth of eastern black nightshade
was reduced by 48, 83, and 98% by shade levels of 60, 80, and 94%, respectively. Berry
number was reduced by 48, 87, and 99% at the same shade levels and berry production
constituted 53, 59, and 40% of the total biomass when grown under these shade levels. At
the lowest growth irradiance, eastern black nightshade utilized nearly half of its biomass
in harvesting the available light, an essential function for a plant that survives extended
periods under the soybean canopy.

Small seeded crops such as tomatoes, however, are not strong competitors and
yields can be reduced severely where nightshades are dense (Tan and Weaver 1997 ).
Weaver et al. (1987) reported an 80% yield loss in direct seeded tomatoes from four
eastern black nightshade per m2, but only 25 to 60% yield loss from the same weed
density in transplanted tomatoes. McGiffen et al.. (1992) reported that five nightshade
plants per m2 can significantly reduce the yield of tomato. Eastern black nightshade at
five plants per m2 resulted in only 21 tomatoes per plant, as opposed to 51 fruit per plant
when tomatoes were weed free. Tomato fruit yield declined exponentially as eastern
black nightshade density increased. Eastern black nightshade reduced tomato yields when
it grew taller than the canopy and shaded the young, actively photosynthesizing tomato
leaves. Blackshaw (1991) reported that as few as two hairy nightshade plants per m
significantly reduced dry bean yield. Interference from hairy nightshade during the first
three weeks after emergence was enough to reduce dry bean yield. Six to nine weeks of
weed free maintenance are needed to attain dry bean seed yields that are comparable to
the weed free. Hairy nightshade seed production per plant decreased from 52,000 to 1900

seeds as hairy nightshade density increased from 2 to 100 plants per meter of bean row.

12

At six weeks after dry bean emergence, only dry bean density affected hairy nightshade
biomass. In that case, less biomass was attained when dry beans were grown at 48 than at
24 plants per m2. As the growing season progressed, the competitive effects of dry bean
on hairy nightshade became more evident. At maturity, hairy nightshade biomass was
progressively reduced as dry bean row spacing was reduced from 69 to 46 to 23 cm.
Additionally, hairy nightshade biomass was reduced when dry bean density was
increased from 24 to 48 plants per m2. At a density of 48 plants per m2, dry bean yield
progressively increased as row spacing was reduced from 69 to 23 cm. Narrow row
spacing and a higher plant density allowed dry bean to capture more PAR at any one time
and also resulted in more complete canopy closure earlier in the growing season. Yield of
dry beans infested with hairy nightshade was likely affected by competition for light

between the two species (Blackshaw et al. 1999).

EFFECT OF SHADE ON PLANT GROWTH

Crops and weeds show varying degrees of shade tolerance. In a study comparing
soybean and weeds commonly associated with soybean, eastern black nightshade, tumble
pigweed, and common cocklebur were the most photosynthetically efficient under low-
growth irradiance due to a combination of physiological and morphological adaptations
(Regnier et al.. 1988; Stoller and Myers 1989a). In contrast to eastern black nightshade,
hairy nightshade, another nightshade species that is common in Michigan, does not
appear to persist in dense shades (Tan and Weaver 1997). The presence of a leaf canopy
alters the quantity as well as the spectral distribution, or quality, of light underneath it.

Many plants possess plasticity to acclimate to reduced light conditions by redistribution

l3

of dry matter, altered leaf anatomy, decreased respiration rates, decreased enzyme
activities, and decreased electron transport capacity (Holt 1995). Reductions in yield of
processing tomato were greater when grown in competition with eastern black nightshade
compared to black nightshade due to the greater height of eastern blaCk nightshade. PAR
at the top of the tomato canopy was positively correlated with yield and negatively
correlated with eastern black nightshade density (McGiffen et al.. 1992). When plant
environments change from high light to a shaded environment (i.e. when a canopy closes)
many weeds respond with adaptations that reduce the growth-limiting effects of shading.
Increased leaf area ratio (LAR) and plant height are common responses to shade that may
offset reductions in photosynthetic rate and biomass production that commonly occur.
However, seed production generally decreases when reductions in light are extreme (Holt
1995)

Leaves absorb light in the blue and red regions and reflect or transmit in the green
and far red regions of the Spectrum. With increasing depth in a plant canopy, light is
enriched in the far red wavelengths and has a lower red: far red ratio. The spectral photon
distribution of radiation within a canopy is severely depleted in the 400 to 700 nm range
and enhanced in wavelengths over 700 nm (far red light). The morphological responses
seen by plants in response to reduced irradiance have been shown to be triggered by
phytochrome in response to the low red: far red ratios under canopies (Taiz and Zieger
2002). These morphological responses include stem elongation, flowering, and changes
in stomatal conductance or plant anatomy. Leaf thinning in shaded conditions has also
been attributed to an increase in the ratio of R: FR light, but may also result from a

decrease of blue light.

14

Weed success depends on survival and some level of reproduction to continue the
species. Knowledge of the responses of hairy nightshade and eastern black nightshade to
different levels of light quantity and quality will allow for the development of

management techniques to enhance control of these weed species.

15

10.

ll.

12.

13

LITERATURE CITED

. Ateh, C.M., and R.G. Harvey. 1999. Annual weed control by glyphosate in

glyphosate—resistant soybean (Glycine max). Weed Tech. 13: 394-398.

Bassett, I.J., and DB. Munro. 1985. The biology of Canadian Weeds. 67.

Solanum ptycanthum Dun., S. nigrum L., and S. sarrachaides Sendt. Can. J. Plant
Sci. 65: 401-414.

Baysinger, J .A., and 3D. Sims. 1991. Giant ragweed (Ambrosia trifida)
interference in soybean (Glycine max). Weed Sci. 39: 358-362.

Blackshaw, RE. 1991. Hairy nightshade (Solanum sarrachoides) interference in
dry bean (Phaseolus vulgaris). Weed Sci. 39: 48-53.

Bloomberg, J .R., B.L. Kirkpatrick, and L.M. Wax. 1982. Competition of common
cocklebur with soybean. Weed Sci. 30:507-513.

Bugert, KL. and QC. Bumside. 1972. Optimum temperature for germination and
seedling development of black nightshade. Res. Rep., North Cent. Weed Control
Conf. 29: 56-57.

Burnside, O.C., and W.L. Coleville. 1964. Soybean and weed yields as affected
by irrigation, row spacing, tillage, and amiben. Weeds. 12: 109-112.

Coble, H.D., F.M. Williams, and R.J. Ritter. 1981. Common ragweed (Ambrosia
artemisiifolia) interference in soybean (Glycine max). Weed Sci. 29: 339-342.

Crook, TM. and K.A. Renner. 1990. Common lambsquarters (Chenopodium

album) competition and time of removal in soybean (Glycine max). Weed Sci. 38:
358-364.

Crotser, MP, and W.W. Witt. 2000. Effect of Glycine max canopy
characteristics, G. max interference and weed-free period on Solanum ptycanthum
growth. Weed Sci. 48: 20-26.

Delannay, X., T.T. Bauman, D.H. Beighley, et al.. 1995. Yield evaluation of
glyphosate-tolerant soybean line after treatment with glyphosate. Crop Sci. 35:
1461-1467.

Etheredge, W.J., Jr., D.A. Ashley, and J.M. Woodruff. 1989. Row spacing and
plant population effects on yield components of soybean. Agron. J. 81: 947-951.

. Givelberg, A. and M. Horowitz. 1984. Germination behavior of Solanum nigrum

seeds. J. Exp. Bot. 35: 588-598.

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14.

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Gonzini, L.C., S.E. Hart, and L.M. Wax. 1999. Herbicide combinations for weed
management in glyphosate resistant soybean (Glycine max). Weed Tech. 13:354-
360.

Holt, J .S. 1995. Plant responses to light: A potential tool for weed management.
Weed Sci. 43: 474-482.

Keely, PE. and R.J. Thullen. 1983. Influence of planting date on the growth of
black nightshade. Weed Sci. 31: 180-184.

Légére, A. and M.M. Shreiber. 1989. Competition and canopy architecture as
affected by soybean (Glycine max) row width and density of redroot pi gweed
(Amaranthus retroflexus). Weed Sci. 37: 84-92.

McGiffen, M.E., Jr., J .B. Masiunas, J .D. Hesketh. 1992. Competition for light
between tomatoes and nightshades (Solanum nigrum or S. ptycanthum). Weed
Sci. 40: 220-226.

Mickelson, J .A., and K.A. Renner. 1997. Weed control using reduced rates of

postemergence herbicides in narrow- and wide-row soybean. J. Prod. Agric. 10:
43 1 -43 7.

Ogg, A.G., Jr., and J .A. Dawson. 1984. Time of emergence of eight weed species.
Weed Sci. 32: 327-335.

Patterson, M.G., R.A. Walker, D.L. Colvin, G. Wehtje, and J .A. McGuire. 1988.
Comparison of soybean (Glycine max) — weed interference from large and small
plots. Weed Sci. 36: 836-839.

Quackenbush, LS, and RN. Anderson. 1984a. Effect of soybean (Glycine max)
interference on eastern black nightshade (Solanum ptycanthum). Weed Sci. 32:
63 8-645.

Quackenbush, LS, and RN. Anderson. 1984b. Distribution and biology of two
nightshades (Solanum spp.) in Minnesota. Weed Sci. 33: 386-390.

Regnier, BE, ME. Salvucci, and E.W. Stoller. 1988. Photosynthesis and growth

response to irradiance in soybean (Glycine max) and three broadleaf weeds. Weed
Sci. 36: 487-496.

Roberts, HA, and J .E. Boddrell. 1983. Field experiments and temperature

requirements for germination in Solanum sarrachoides Sendt. Weed Res. 23: 247-
252.

Roberts, H.A., and RM. Lockett. 197 8. Seed dormancy and field emergence in
Solanum nigrum L. Weed Res. 18: 231-241.

17

27.

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Rogers, BS, and AG. Ogg, Jr. 1989. Taxonomy, distribution, biology, and
control of black nightshade (Solanum nigrum) and related species in the United
States and Canada. Rev. Weed Sci. 4: 25-58.

Shibles, R.M., and C. R. Weber. 1966. Interception of solar radiation and dry
matter production by various soybean planting patterns. Cr0p Sci. 6: 55-59.

Stoller, E.W. and RA. Myers. 1989a. Response of soybean (Glycine max) and
four broadleaf weeds to reduced irradiance. Weed Sci. 37: 570-574.

Stoller, E.W. and RA. Myers. 1989b. Effects of shading and soybean interference
on eastern black nightshade growth and development. Weed Res. 29: 307-316.

Taiz, L. and E. Zieger. 2002. Phytochrome and Light Control of Plant
Development fiant Physiology. Third Edition. Sinauer Associates, Inc.
Publishers, Sunderland, Massachusetts. p. 375-417.

Tan, CS, and SE. Weaver. 1997. Water use patterns of eastern black nightshade
(Solanum ptycanthum) and hairy nightshade (Solanum sarrachoides) in response
to shading and water stress. Can. J. Plant Sci. 77: 261-265.

Taylor, ELM. 1980. Soybean growth and yield as affected by row spacing and by
seasonal water supply. Agron. J. 72: 543-547.

Taylor, H.M., W.K. Mason, A.T.P. Bennie, and HR. Rowse. 1982. Response of
soybean to two row spacings and two soil water levels. I. An analysis of biomass

accumulation, canopy development, solar radiation interception, and components
of seed yield. Field Crops Res. 5: l-14.

Thomson, CE, and W.W. Witt. 1987. Germination of cutleaf groundcherry
(Physalis angulata), smooth groundcherry (Physalis virginianca) and eastern
black nightshade (Solanum ptycanthum). Weed Sci. 35: 58-62.

Toole, E.H., and E. Brown. 1946. Final results of the Duvel buried seed
experiment. J. Agric. Res. 72: 201-210.

Vandeventer, J .W., W.F. Meggitt, and D. Penner. 1982. Morphological and

physiological variability in black nightshade (Solanum spp.) Pestic. Sci. 13: 257-
262.

Weaver, S.E., N. Smits, and CS. Tan. 1987. Estimating yield loss of tomatoes
(Lycopersicon esculentum) caused by nightshade (Solanum spp.) interference.
Weed Sci. 35: 163-168.

18

39. Young, B.G., J .M. Young, L.C. Gonzini, S.E. Hart, L.M. Wax, and G. Kapusta.
2001. Weed management in narrow- and wide-row glyphosate resistant soybean
(Glycine max). Weed Tech. 15: 112-121.

19

CHAPTER 2
NARROW ROW SPACING INCREASED CONTROL OF EASTERN BLACK
NIGHTSHADE (Solanum ptycanthum) IN GLYPHOSATE- RESISTANT
SOYBEAN (Glycine max) IN MICHIGAN

Abstract. Field studies were conducted to evaluate the effect of soybean row spacing and
soybean populations on the emergence and growth of eastern black nightshade in
glyphosate-resistant soybean. Eastern black nightshade emerged 15 to 20 days after
soybean planting and emergence ceased approximately 40 days after planting when
soybean were at the V5 stage of growth. There was no difference in eastern black
nightshade emergence regardless of soybean row spacing and populations in all site
years. One application of glyphosate controlled eastern black nightshade in this study.
Soybean leaf area index was greatest for soybean planted in 19 cm rows at the peak of the
growing season, regardless of soybean population. Soybean planted in 19 cm rows at
populations of 308 000, 432 000, and 556 000 seeds/ha were more competitive than
soybean planted at 185 000 seeds/ha in 76 cm rows. Seeding rates of 308 000 and 432
000 seeds/ha effectively reduced eastern black nightshade growth in 76 cm rows.
Soybean yield at East Lansing in 2001 was not greater in narrow rows compared to 76 cm
rows when eastern black nightshade was controlled. Eastern black nightshade densities of
2 to 7 plants/m2 reduced the yield of soybean planted at populations of 308 000 and 556
000 in 19 cm rows and 185 000 seeds/ha in 76 cm rows in 1 of 3 site years.
KEY WORDS: soybean populations, row spacing, eastern black nightshade (Solanum

ptycanthum)

20

INTRODUCTION

Weed interference with soybean can reduce yield and soybean plant dry weight
(Légére and Schreiber 1989). As few as four common ragweed (Ambrosia artemisiifolia
L.) plants per 10 m of row reduced soybean yields (Coble et al. 1981). Full season
interference from four common cocklebur (Xanthium strumarium) per 10 m of row
reduced soybean yields by an average of 13% (Bloomberg et al.. 1982). Soybean yield
was reduced 46 to 52% by 3 giant ragweed (Ambrosia trifida L.) plants per 10 m of row,
respectively (Baysinger and Sims 1991). Common lambsquarters (Chenopodium album)
at a density of 32 plants per 10 m of soybean row reduced soybean yields by 20% when
common lambsquarters were present all season (Crook and Renner 1987). Eastern black
nightshade (Solanum ptycanthum) densities of 2 plants per m2 did not reduce soybean
yield, indicating that eastern black nightshade is not a strong competitor with soybean
(Crotser and Witt, 2000).

In recent years, growers have become interested in planting soybean in narrow
row widths because of potentially higher yields and better weed control. Soybean planted
in 25 cm rows yielded 39% more than soybean in 100 cm rows when planted at 101
kg/ha (Burnside and Coleville 1964). Ethredge et al. (1989), reported that soybean yield
increased as row spacing decreased from 76-, to 51-, to 25-cm when averaged over two
soybean cultivars and three plant populations. The yield increase of narrow row soybean
can be attributed to the development of a canopy that provides complete ground cover
before the time that pod-fill occurs. Full ground canopies intercept more solar radiation
and have greater photosynthesis than do partial ground cover canopies (Shibles and

Weber 1966). With the same leaf area index in narrow and wide rows, there was greater

21

light interception in narrow rows because of a more uniform leaf distribution, which
resulted in higher yield (Taylor et al. 1982).

When soybean are planted in narrow rows, weed biomass is reduced (Patterson et
al. 1988). Post emergence herbicide treatments in narrow rows resulted in 30% less weed
biomass than the same treatments in wide row soybean (Mickelson and Renner 1997).
Plant populations were 469 500 seeds per ha in 19 cm row spacing and 358 000 seeds per
ha in the 76 cm row spacing. Redroot pigweed total leaf area was reduced in narrow row
soybean compared to wide row soybean (Le'gere and Schreiber 1989).

Glyphosate is now widely used for controlling summer annual weeds in
glyphosate resistant soybean (Delannay et al. 1995). Glyphosate controls a broad
spectrum of grass and broadleaf weeds, has a favorable environmental profile, a low
mammalian toxicity, and is an alternative to the acetolactate synthase inhibiting
herbicides. However, glyphosate does not have soil residual activity, which allows weeds
to emerge after herbicide application if light and moisture are available. In Wisconsin,
weeds were consistently controlled in 20 cm rows due to early canopy closure and
shading of subsequent flushes (Ateh and Harvey 1999). Adding imazethapyr, which has
soil residual activity, to a glyphosate application at the V4 stage of soybean (Ritchie et a1.
1997) did not improve weed control compared to glyphosate alone.

Sequential applications of glyphosate may increase overall weed control and
reduce the risk of yield reductions due to weed competition (Gonzini et al. 1999).
Properly timed sequential applications could eliminate weeds before weed competition
occurs and could control later emerging weeds. However, by planting soybean in narrow

rows, sequential applications of glyphosate to control late emerging weeds may be

22

unnecessary. Weed control by a single application of glyphosate was improved by the use
of 19- or 38- cm rows compared to 76-cm rows in southern Illinois (Young et al. 2001).

Shade effectively inhibits the growth of many weeds. Eastern black nightshade
can be a problem in soybean fields because it can grow in the shaded environment that
exists beneath the soybean canopy (Stoller and Myers 1989a). Eastern black nightshade
interferes with soybean harvest and reduces crop quality because the juice from ruptured
berries stains soybean seeds (Quackenbush and Anderson 1984a). Eastern black
nightshade problems, however, can be reduced by increasing the competition from
soybean plants. Eastern black nightshade emergence and survival was greatly reduced
once the soybean canopy began to close. Nightshades planted 3 wk or more after soybean
produced 10 or fewer berries per plant (Quackenbush and Anderson 1984a). By
narrowing rows to 38 cm, eastern black nightshade growth and berry production was
reduced by 50% in Illinois (Stoller and Myers 1989b). However, even the smallest
eastern black nightshade plants produced some reproductive growth by the last harvest
date, contributing seeds to the soil seed bank for future infestations as well as creating the
potential to stain soybean seed and impede harvest (Crotser and Witt 2000).

The objectives of this study were to determine the influence of soybean row
spacing and soybean population on the emergence and grth of eastern black
nightshade. The influence of soybean plant population on eastern black nightshade
emergence and growth has not been reported previously. Furthermore, we determined if a
residual herbicide was necessary for season long control of eastern black nightshade
following a glyphosate application in soybean planted at three populations in two row

spacings. Residual herbicides are an expense to the grower and can influence crop

23

rotation the following year. Residual herbicides may not be necessary to stop eastern
black nightshade emergence and growth in high populations of soybean planted in narrow

rows because of faster canopy closure resulting in reduced irradiance.

24

MATERIALS AND METHODS

Field experiments were conducted in 2001 and 2002 to evaluate the emergence
and growth of eastern black nightshade in glyphosate-resistant soybean. In 2001 and
2002, research was conducted at the Michigan State University Crop and Soil Science
Research Farm in East Lansing, MI. In 2002, research was conducted at this farm and at
the Michigan State University Horticultural Experiment Station in Clarksville, MI. The
soil at East Lansing was a Capac sandy clay loam (fine-loamy, mixed, mesic Aerie
Ochraqualfs) with 2.5% organic matter and a pH of 6.4 in 2001. This site was moldboard
plowed the previous fall and field cultivated twice in the spring. In 2002, the soil at East
Lansing was a Capac sandy clay loam with 2.5% organic matter and a pH of 7.0. The soil
at Clarksville was a Lapeer loam (coarse-loamy, mixed, mesic Mollic Haplaquepts) with
1.5% organic matter and a pH of 6.6. This site was chisel plowed and field cultivated
twice in the spring of 2002.

In 2001, DeKalb CX 242 soybean were planted in 19 and 76 cm rows at 308 000,
and 432 000 seeds ha'l. In 2002, DeKalb CX 23-51 soybean were planted at populations
of 308 000, 432 000, and 556 000 seeds ha'1 in 19 cm rows and 185 000, 308 000, and
432 000 seeds ha" in 76 cm rows. Both varieties were mid-group 2 soybean. Soybean
were planted in 19 cm row spacings with a Great Plains Solid Stand 101 grain drill in
2001 and a John Deere 15602 grain drill at East Lansing and a John Deere 750 grain drill
at Clarksville in 2002. Soybean were planted in 76 cm row spacing with a John Deere
7200 Max-Emerge® 2 planter at East Lansing both years and a John Deere 7000 planter

at Clarksville in 2002. Plots at East Lansing were 3 m wide and 9.1 m long in 2001 and 3

 

' Great Plains Manufacturing Inc., PO. Box 218, Assaria, KS 67416.

2 Deere and Co., 501 River Drive, Moline, IL 61265-1100.

25

m wide and 10.7 m long in 2002. Plots in Clarksville were 4.6 m wide and 12.2 m long in
2002.
Eastern Black Nightshade Emergence

Eastern black nightshade seed3 was spread across the field to ensure a uniform
population at each location in each year. Quadrats (0.19 m2) were placed within and
between the soybean rows in the plots receiving the glyphosate application. Quadrat
locations were marked at the time of the first emergence count so that the same area was
evaluated each time. Seedlings were left undisturbed as they were counted. Emergence
counts were taken weekly throughout the growing season.
Herbicide Applications

A preemergence application of cloransulam methyl at 17.7 g a.i. per hectare was
applied to the entire field sites both years to control other broadleaf weeds besides eastern
black nightshade; cloransulam methyl has no effect on eastern black nightshade
(Anonymous 2003). Postemergence herbicide treatments each year included glyphosate
at 650 g ae ha'l, glyphosate + imazethapyr at 650 g ae ha'1 and 70 g ai ha'l, respectively,
and an untreated control. All herbicide treatments included 21 g ammonium sulfate per L
of spray solution. A weed free plot was present in each replication that was not taken to
yield for the purpose of soybean canopy measurements and emergence counts. The weed
free plots received an application of glyphosate as needed. All postemergence treatments

were applied to soybean at V3 and eastern black nightshade with 3 to 6 leaves and 2.5 cm

tall.

 

3 v & J Seed, Po. Box 82, Woodstock, IL 60098.

26

Preemergence herbicide applications were made with a Wilrnar sprayer traveling
at 10.3 km/h and delivering 187 L/ha at 207 kPa of pressure on 14 May 2001 and 15 May
2002 in East Lansing. Preemergence herbicide application in Clarksville was made with a
tractor mounted compressed air sprayer traveling at 6.3 km/h and delivering 178 L/ha at
207 kPa of pressure on 22 May 2002. Postemergence herbicide applications were made
with a tractor mounted compressed air sprayer traveling at 6.3 km/h and delivering 178
L/ha at 207 kPa of pressure on 23 June 2001 and 22 June 2002 in East Lansing and 24
June 2002 in Clarksville. Treatments were made with 8003 flatfan nozzles4 on a 51 cm
spacing at 61 cm above the crop and weed canopy. Air temperature at East Lansing was
28° C with 48% relative humidity in 2001 and 28° C with 51% relative humidity in 2002
at the time of application. Air temperature at Clarksville was 31° C with 35% relative
humidity at the time of application.

Soybean Canopy Development

The amount of light transmitted through the soybean canopy was measured every
1 to 2 weeks at or near solar noon at each site beginning in early July until the canopy
began to senesce in early September. Measurements were taken only in weed free plots
using a SunScan Canopy Analysis System.5 The SunScan system consists of three
components: 1) a wand that is 1 m long and 13 mm wide with sensors placed every 15.6
mm along the length of the wand with a spectral response of 400-700 nm to measure light
beneath the crop canopy, 2) a tripod-mounted sensor to measure both incident and diffuse
light above the crop canopy, and 3) a handheld Psion Workabout datalogger6 that

combined simultaneous measurements of light above and beneath the crop canopy. Light

 

4 Teejet flat fan tips. Spraying Systems Co., North Ave. and Schmale Road, Wheaton, IL 60188.
5 Delta-T Devices LTD, 128 Low Road, Burwell, Cambridge CB5 OEJ, England.
6 Gylling Data Management Co. Inc., 405 Martin Blvd., Brookings, SD 57006.

27

transmission, as a percent of incident, was automatically calculated as each measurement
was taken perpendicular to the soybean row from the weed free plots.
Eastern Black Nightshade Biomass

Eastern black nightshade biomass was sampled on 20 October 2001 and 1
October 2002 in East Lansing and on 27 September 2002 in Clarksville by harvesting all
aboveground portions of each eastern black nightshade plant from a 0.19 m2 quadrat
placed randomly within the plot. Eastern black nightshade was harvested and counted
from two areas per plot, oven dried, and weighed.
Microplots

In 2002, microplots were established in East Lansing and Clarksville to study
further the effects of soybean population and row spacing on nightshade growth and
development. These microplots were 3.8 m x 3.8 m in size. Soybean were over seeded in
19 cm and 76 cm rows and thinned to desired populations of 308 000, 432 000, and 556
000 plants per hectare in the 19 cm rows and 185 000, 308 000, and 432 000 plants per
hectare in the 76 cm rows. Postemergence herbicide treatments at each location included
glyphosate at 650 g ae ha’1 and an untreated control. Postemergence herbicide
applications were made with a tractor mounted compressed air sprayer traveling at 6.3
km/h and delivering 178 L/ha at 207 kPa of pressure on 22 June 2002 in East Lansing
and 24 June 2002 in Clarksville when soybean were at V3 stage of growth and
nightshade was 2.5 cm tall. Treatments were made with 8003 flat fan nozzles7 on a 51 cm
spacing at 61 cm above the crop and weed canopy. Nightshade biomass measurements
(plant number, total dry weight, berry dry weight) were taken on July 9, August 6, and

September 27 at East Lansing and July 10, August 8, and October 1 at Clarksville by

 

7 Teejet flat fan tips. Spraying Systems Co., North Ave. and Schmale Road, Wheaton, IL 60188.

28

harvesting all aboveground portions of each eastern black nightshade plant from a 0.19
m2 quadrat placed randomly within the microplot. Eastern black nightshade was counted,
oven-dried, and weighed. Berries were weighed separately from the leaves and stems for
the August and October harvest dates. Soybean yield was determined by harvesting the
center rows of each plot with a plot combine. Soybean yields were taken on 1 October
2002 at both locations. Seed yields were adjusted to 13% moisture.
Soybean Yield

Soybean yield was determined by harvesting the center rows of each plot with a
Massey 8XP self propelled plot harvesting combine with onboard harvest yield and
moisture equipment. Soybean was harvested on 28 October 2001 and 1 October 2002 at
both East Lansing and Clarksville. Seed yield was adjusted to 13% moisture. All eastern
black nightshade plants remaining in the plots were removed by hand prior to harvest so
that eastern black nightshade berries would not be weighed with the soybean seed.
Statistical Analysis

The experimental design was a split-split plot design with four replications. The
main plot was row spacing, the sub-plot was soybean population, and the sub-sub-plot
was herbicide treatment. Data were subjected to analysis of variance using the PROC
MIXED procedure in SAS and means were separated using Fishers Protected LSD at O. =
0.05. Results are presented separately by year and location since additional soybean
populations were included in 2002. Results are presented separately for each location in

2002 where year*location interactions exist.

29

RESULTS AND DISCUSSION

Eastern Black Nightshade Emergence

Eastern black nightshade emerged 15 - 20 days after soybean planting in 2001 and
2002 (Figure 1, 2, 3). In both years, emergence of black nightshade ceased approximately
40 days after planting when soybean were at the V5 stage (Ritchie et al. 1997). Ogg and
Dawson (1984) reported that most of the seedlings of eastern black nightshade emerged
within a 2 month period in the spring. Similar results were reported by Roberts and
Boddrell (1983) and Roberts and Lockett (1978) working in England, and Quackenbush
and Anderson ( 1984) in Minnesota. This indicates that eastern black nightshade may not
be a late emerging species as previously reported. Optimum germination of eastern black
nightshade was at a constant 30°C or at alternating temperatures of 30/20° C (Thompson
and Witt, 1987). Bugert et al. (1973) reported that eastern black nightshade seeds
germinated in the field when soil temperatures were between 20° C and 46° C, but the
optimum temperature for emergence was 25° to 30°C. On 8 August 2001, the maximum
soil temperature was 41° C at East Lansing. On 4 July 2002, the maximum soil
temperature was 29° C at East Lansing and 33° C at Clarksville. Rainfall was above
average in May for both 2001 and 2002 (Table 1), however, rainfall was below average
in June of both years at East Lansing and July 2002 at Clarksville. At East Lansing,
eastern black nightshade may have ceased to emerge in 2001 due to dry soil conditions
and high soil temperatures. In 2002, at East Lansing and Clarksville, eastern black
nightshade probably ceased to emerge due to dry soil conditions.

There was no difference in eastern black nightshade emergence due to soybean

row spacing and population in 2001 (Figure 1) or in 2002 at either location (Figure 2).

30

The total number of seedlings that emerged varied widely between years and locations.
Natural populations of eastern black nightshade seeds in the soil as well as the seeded
population probably account for emergence during this time period. It appears that
shading from the soybean had no effect on eastern black nightshade emergence. We
observed no difference in eastern black nightshade emergence adjacent to or between the
soybean rows in our biweekly quadrant counts. Light is required for the germination of
eastern black nightshade seeds. Thompson and Witt (1987 ) reported that in the dark,
eastern black nightshade seed germinated poorly over all temperature regimes. Eastern
black nightshade germination was enhanced by light and within the visible spectrum red
light was most effective in enhancing germination (Givelberg and Horowitz 1984). Light
was not limited by the soybean canopy in the forty days following soybean planting
because at 50 days after planting (DAP) the LAI was still less than one (Figures 3 and 4).
Therefore, eastern black nightshade had light available for germination and emergence.
Herbicide Applications

One application of glyphosate at the V3 stage of soybean controlled eastern black
nightshade in 2001 and 2002. Since eastern black nightshade did not emerge later in the
growing season afier the herbicide application, a residual herbicide, such as imazethapyr,
was not needed for season long control of eastern black nightshade in this study. Rainfall
in July and August of 2001 and in 2002 was below average in both years of this study
(Table 1). This may have contributed to the lack of late season eastern black nightshade
emergence. In a year with normal rainfall, a residual herbicide would be needed to
control late emerging eastern black nightshade if emergence was not limited by high soil

temperature. It would be of interest to study eastern black nightshade emergence in a

31

field with no soybean canopy to determine if eastern black nightshade would continue to
emerge throughout the summer if adequate rainfall occurred. Furthermore, the study of
seed emergence patterns collected from plants growing in a single field would be of
interest to determine if Keely and Thullen’s (1983) report of late forming seed requiring
higher temperatures for germination is supported, and if eastern black nightshade seed
from shaded areas requires a lengthier after ripening period (Stoller and Myers 1989b).
These factors could result in a species ‘Shifi’ in narrow row soybean to eastern black
nightshade p0pulations that emerge later when soil temperatures are warmer.

Soybean Canopy Development

In 2001, early in the growing season, soybean planted in 76 cm row spacing had a
higher leaf area index (LAI) than those planted in the drilled rows (Figure 3a). However,
at the peak of the soybean canopy (approximately 105 days after planting), soybean
planted in 19 cm rows at both populations had greater LAI than those planted in the 76
cm row spacing. This indicates that soybean planted in 19 cm row spacings have a greater
ability to compete for light with eastern black nightshade than those planted in 76 cm row
spacings.

We saw a similar pattern in 2002 at both locations, with soybean planted in the 19
cm row at populations of 432 000 and 556 000 seeds/ha having a greater LAI than those
planted in the 76 cm row spacing (Figure 3b and 3c). However, the difference in LAI was
seen much earlier in 2002 (50 to 70 DAP) than in 2001 (105 DAP), indicating that in
2002, eastern black nightshade grth would have been affected for a longer period of

time. At the end of the growing season in 2002 at Clarksville, soybean planted in 76 cm

32

rows had a greater LAI than those in the 19 cm row spacing. This is because of some
soybean lodging that occurred in the drilled soybean.

Therefore, row spacing had a greater influence on LAI than plant population. In
fact, soybean population had a negligible affect on canOpy development and closure.
Eastern black nightshade growth will be suppressed by planting in narrow rows due to
increased soybean LAI, regardless of soybean population. However, the lack of soil
moisture may have inhibited soybean growth and yield potential, particularly at 556 000
seeds/ha in 19 cm rows. Taylor (1980) reported that in years where water is limiting, row
spacing had no effect on soybean yield. The increased interception of solar radiation
caused by the more even distribution of plants growing in narrow rows resulted in more
water use during the early growing season and less water remaining during pod fill.
Higher populations, regardless of row spacing, would therefore not be able to maximize
canopy development and yield in years where rainfall is limited in August during time of
pod-fill (Table 1).

Eastern Black Nightshade Biomass

In 2001, soybean row Spacing or plant population did not reduce the density or
dry weight of eastern black nightshade in October (Table 2). Densities of eastern black
nightshade in October were approximately 85% less than densities measured in June
(Figure 1). This indicates that there is attrition of eastern black nightshade plants when in
competition with soybean. Self thinning due to intraspecific competition has been
reported extensively in the ecological literature. The term self thinning refers to the
density dependent mortality in plant populations. The severity of self thinning is affected

by environmental conditions such as moisture and light (Harper 1977). However, in most

33

weed competition studies in soybean, the established weed density are reported, and not
the weed density at the time of harvest.

In 2002, eastern black nightshade density within each row spacing was not
affected by soybean population. However, eastern black nightshade density was reduced
in the 19 cm rows compared to the 76 cm row spacing at East Lansing, when averaged
over plant populations. At Clarksville, soybean planted at 556 000 seeds/ ha in the 19 cm
row spacing had a significantly lower eastern black nightshade density than those planted
at 185 000 seeds/ ha in the 76 cm row spacing (Table 3). Since there were no differences
in eastern black nightshade emergence in May and June due to soybean row spacing or
population, early season eastem black nightshade emergence will not be influenced by
soybean row spacing or population.

Eastern black nightshade total dry weight per plant at East Lansing and
Clarksville was reduced in the 19 cm row spacing at all populations compared to 185 000
seeds/ha 76 cm row spacing (Table 3). Stoller and Myers (1989b) found that eastern
black nightshade that emerged with soybean and grew in the open spaces between rows
75 cm apart produced 43 g dry weight and 264 berries per plant, whereas, nightshades
that grew between rows spaced 33 cm apart produced an average of less than 1 g dry
weight and less than 1 berry per plant. Quackenbush and Anderson (1984) reported that
eastern black nightshade planted in May with soybean in narrow rows (18 cm) produced
50% fewer berries than did plants in soybean in wide (7 6 cm) rows. Our results indicate
that soybean planted in the 19 cm row spacing, regardless of soybean population, are
more competitive than soybean planted at 185 000 seeds/ha in 76 cm rows. Therefore,

seeding rates of 308 000, 432 000 and 556 000 seeds/ha in drilled soybean effectively

34

reduced eastern black nightshade growth. Seeding rates of 308 000 and 432 000
effectively reduced eastern black nightshade growth in 76 cm rows also. It would be of
interest to plant soybean at 185 000 seeds/ha in 19 cm rows to determine if this low of a

population would supress eastern black nightshade growth.

Microplots

In 2002 at East Lansing, planting soybean in 19 cm rows did not reduce the
density of eastern black nightshade in July compared to 76 cm rows, regardless of
soybean plant population (Table 4a). There were no differences in soybean canopy at this
point of the growing season, so there was light available for nightshade growth,
regardless of row spacing or plant population. However, by August (p= 0.0414) and
October (p=0.0181), eastern black nightshade density was significantly reduced in 19 cm
rows compared to 76 cm rows, regardless of soybean plant population. LAI of soybean in
19 cm row spacings was greater than the LAI of soybean in 76 cm soybean. Furthermore,
there was more light available in soybean planted in 76 cm row spacing at 185 000
seeds/ha population for eastern black nightshade growth compared to light at 432 000
seeds/ha in 76 cm rows (Figure 4a and 4b). At Clarksville, eastern black nightshade
density was greater in the 76 cm rows at populations of 185 000 and 308 000 seeds/ha
compared to the 19 cm rows at a population of 556 000 seeds/ha in July (Table 4b). In
August, the soybean planted in 76 cm rows at a population of 432 000 seeds/ha had a
significantly higher eastern black nightshade density compared to soybean planted in 19
cm rows at 308 000 and 432 000 seeds/ha. By October, eastern black nightshade density

was significantly (p= .0353) greater in 76 cm rows at a population of 308 000 seeds/ha

35

compared to 432 000 seeds/ha in 19 cm rows. This difference may be attributed to
eastern black nightshade attrition in the 19 cm row spacing. The soybean canopy was
greatest in 76 cm rows in Clarksville in late August due to soybean lodging that took
place in the 19 cm row soybean, which allowed for more light available for nightshade
grth in the 19 cm rows late in the growing season.

The total dry weight per plant of eastern black nightshade at East Lansing was
reduced in the 19 cm compared to 76 cm rows in July and August, but not in October
(Table 5). Berry dry weight at East Lansing was also similar in 19 cm compared to 76 cm
rows, although there was a strong trend to indicate that eastern black nightshade growing
in 19 cm rows produced fewer berries than those in 76 cm rows (Table 6). In contrast, at
Clarksville, eastern black nightshade total dry weight per plant was reduced in 19 cm
rows compared to 76 cm rows in all three harvest months, when averaged over row
spacings (Table 5). By October, the dry weight of eastern black nightshade berries
produced in 19 cm row soybean was significantly reduced compared to berry dry weight
in the 76 cm rows.

The density of eastern black nightshade density in microplots was greater at East
Lansing than at Clarksville throughout the growing season. There was probably more
intraspecific competition at East Lansing compared to Clarksville. This is evident by
looking at the eastern black nightshade dry weight per plant. The plants at Clarksville
were larger than those at East Lansing. Eastern black nightshade plants growing in the 76
cm row spacing at Clarksville were able to grow larger and produce more berries due to

less competition with other eastern black nightshade plants. Eastern black nightshade at

36

East Lansing was not only competing with the soybean for light, moisture and nutrients,
but was also competing with other nightshade plants.

Soybean population did not have a significant effect on eastern black nightshade
biomass at either location. There was no significant difference in soybean canopy due to
plant population, therefore, eastern black nightshade berry dry weight and biomass was
not affected by soybean population. Our results are similar to those findings of other
researchers. Crotser and Witt (2000) found that soybean competition greatly reduced
eastern black nightshade growth. In Illinois, eastern black nightshade that emerged with
the crop and grew in the open space between 76 cm rows produced 43 g dry weight and
264 berries per plant, whereas, nightshades that grew between rows spaced 33 cm apart
only produced 1 g dry weight and less than 1 berry per plant (Stoller and Myers, 1989a).
In Minnesota, eastern black nightshade planted in May with soybean in narrow (19 cm)
rows produced 50% less berries than did plants in wide (76 cm) rows (Quackenbush and
Anderson, 1984). The populations in these studies were equal in narrow versus wide
rows. Our micro-plot data supports our main plot data that low populations of soybean
planted in 76 cm had larger eastern black nightshade plants. The low population of
soybean allowed for more eastern black nightshade growth.

Micro-plot yields

Soybean yield in the micro-plots did not increase in narrow rows compared to 76
cm rows when weeds were controlled at East Lansing. Soybean planted in 19 cm rows at
556 000 seeds/ ha had a greater yield than those planted in 76 cm rows at 432 000
seeds/ha at Clarksville. There were no differences in yield within soybean row spacing

and plant population between the plots with eastern black nightshade and the weed free

37

plots indicating that eastern black nightshade at densities of 3 to 14 plants/m2 in August
at Clarksville or 13 to 24 plants/m2 did not reduce soybean yield.
Soybean Yield

In 2001, soybean yield at East Lansing was not greater in narrow rows compared
to 76 cm rows when weeds were controlled. Rainfall was below average in July and
August of 2001 , therefore, soybean yield was not greater in narrow rows as expected in a
normal rainfall year. Eastern black nightshade did not decrease soybean yield compared
to the glyphosate treatment in 19 cm rows. However, soybean yield was reduced in 76 cm
rows when planted at 432 000 seeds/ha. The addition of imazethapyr to glyphosate did
not increase yield compared to glyphosate alone because no eastern black nightshade
emerged after the glyphosate application.

In 2002, soybean yield at East Lansing was not greater in 19 cm rows compared
to 76 cm rows, regardless of plant population. Rainfall in August was 50% below the 30
year average (Table 1). Eastern black nightshade did not reduce yield in soybean planted
in 19 cm rows. However, eastern black nightshade reduced soybean yield in the untreated
control compared to glyphosate alone in soybean seed in 76 cm rows at 432 000 seeds/ha.
An eastern black nightshade density of 5 plants per m2 at harvest reduced the soybean
yield in this population. Furthermore, in the untreated control treatments, yield was
reduced in the 76 cm seeded at 185 000 seeds/ha compared to 76 cm seeded at 432 000
seeds/ha. There were no significant differences in eastern black nightshade biomass
between these two treatments at soybean harvest. Yield of soybean treated with
glyphosate + imazethapyr was equal to the yield of soybean treated with glyphosate alone

in 19 cm rows and in 76 cm rows at seeded populations of 185 000 and 308 000 seeds/ha.

38

At 432 000 seeds/ha, the soybean yield in the glyphosate treatment was greater than the
yield of glyphosate + imazethapyr. This cannot be attributed to weed control or visible
soybean injury, as there were no weeds present in either of these treatments alter the
herbicide applications were made and no visible injury to the soybean was observed after
the herbicide application.

At Clarksville in 2002, soybean yield in the glyphosate only treatment in 19 cm
rows at a population of 308 000 seeds/ha was greater than yield of the same population in
the 76 cm rows. Eastern black nightshade decreased soybean yield in 19 cm rows at 308
000 and 556 000 seeds/ha. Eastern black nightshade also decreased soybean yield when
seeded at 185 000 seeds/ha in 76 cm rows. An eastern black nightshade density of 7
plants per m2 for soybean seeded at 185 000 seeds/ha in 76 cm rows reduced soybean
yield by 10%. Eastern black nightshade densities of 4 and 2 plants per m2 reduced yield
by 14% and 6% for soybean planted in 19 cm rows at 308 000 and 556 000 seeds/ha.
Glyphosate + imazethapyr reduced yield in 76 cm rows at a population of 432 000 and 19
cm rows at a population of 308 000.

In conclusion, planting soybean in 19 cm rows at populations of 308 000, 432
000, and 556 000 seeds/ha is likely to reduce the number of eastern black nightshade
plants that survive and produce seed. Planting soybean in 76 cm rows at 308 000 and 432
000 seeds/ha may also reduce the survival and competiveness of eastern black
nightshade. Only one application of glyphosate was needed in this study to control
eastern black nightshade in both 19 cm and 76 cm rows, regardless of plant population.
Nightshade that emerged in soybean planted in 19 cm row spacings were smaller and

produced fewer berries compared to those that emerged in 76 cm rows, regardless of

39

soybean population. Planting soybean at higher populations in 19 cm or 76 cm row
spacing did not increase soybean yield in years of limited soil moisture. Furthermore,
increased soybean population in narrow rows had no additional beneficial effect on
eastern black nightshade emergence and growth. Therefore, the increased cost of soybean
seed for high populations in narrow rows was not justified for decreasing eastern black
nightshade emergence, growth or seed production. Seed p0pulations of 308 000 and 432
000 in 76 cm row soybean were beneficial in reducing eastern black nightshade dry
weight per plant in 1 of 3 site years. Eastern black nightshade at densities of 2 to 7 plants
per m2 reduced the yield of soybean planted at populations of 308 000 and 556 000

seeds/ha in 19 cm rows and 185 000 seeds/ha in 76 cm rows in 1 of 3 Site years.

40

10.

11.

12.

13.

Literature Cited

. Ateh, C.M., and R.G. Harvey. 1999. Annual weed control by glyphosate in

glyphosate-resistant soybean (Glycine max). Weed Tech. 13: 394-398.

Baysinger, J .A., and RD. Sims. 1991. Giant ragweed (Ambrosia trifida)
interference in soybean (Glycine max). Weed Sci. 39: 358-362.

Bloomberg, J .R., B.L. Kirkpatrick, and L.M. Wax. 1982. Competition of common
cocklebur with soybean. Weed Sci. 30:507-513.

Burnside, DC. and W.L. Coleville. 1964. Soybean and weed yields as affected by
irrigation, row spacing, tillage and amiben. Weeds. 12: 109-112.

Coble, H.D., F.M. Williams, and R.J. Ritter. 1981. Common ragweed (Ambrosia
artemisiifolia) interference in soybean (Glycine max). Weed Sci. 29: 339-342.

Crook, T.M. and K.A. Renner. 1990. Common lambsquarters (Chenopodium

album) competition and time of removal in soybean (Glycine max). Weed Sci. 38:
358-364.

Crotser, MP, and W.W. Witt. 2000. Effect of Glycine max canopy
characteristics, G. max interference and weed-free period on Solanum ptycanthum
growth. Weed Sci. 48: 20-26.

Delannay, X., T.T. Bauman, D.H. Beighley, et a1... 1995. Yield evaluation of
glyphosate-tolerant soybean line after treatment with glyphosate. Crop Sci. 35:
1461-1467.

Etheredge, W.J., Jr., D.A. Ashley, and J .M. Woodruff. 1989. Row spacing and
plant population effects on yield components of soybean. Agron. J. 81: 947- 951.

Gonzini, L.C., S.E. Hart, and L.M. Wax. 1999. Herbicide combinations for weed
management in glyphosate resistant soybean (Glycine max). Weed Tech. 13:354-
360.

Harper, John L. 1977. Influence of density on yield and mortality in Population
Biology of Plants. Academic Press Inc., San Diego, CA 92101.

Légére, A. and M.M. Shreiber. 1989. Competition and canopy architecture as
affected by soybean (Glycine max) row width and density of redroot pigweed
(Amaranthus retroflexus). Weed Sci. 37: 84-92.

Mickelson, J .A., and K.A. Renner. 1997. Weed control using reduced rates of

postemergence herbicides in narrow- and wide-row soybean. J. Prod. Agric. 10:
43 1-43 7.

41

14.

15.

l6.

17.

18.

19.

20.

21.

22.

Patterson, M.G., R.A. Walker, D.L. Colvin, G. Wehtje, and J .A. McGuire. 1988.
Comparison of soybean (Glycine max)- weed interference from large and small
plots. Weed Sci. 36: 836-839.

Quackenbush, LS, and RN. Anderson. 1984a. Effect of soybean (Glycine max)
interference on eastern black nightshade (Solanum ptycanthum). Weed Sci. 32:
63 8-645.

Quackenbush, LS, and RN. Anderson. 1984b. Distribution and biology of two
nightshades (Solanum spp.) in Minnesota. Weed Sci. 33: 386-390.

Ritchie, Steven W., John J. Hanway, Harvey E. Thompson, Garren O. Benson.
How a Soybean Plant Develops. Special Report No. 53. Iowa State University of
Science and Technology Cooperative Extension Service. Ames, Iowa. June 1997.

20 pp.

Shibles, RM, and CR. Weber. 1966. Interception of solar radiation and dry
matter production by various soybean planting patterns. Crop Sci. 6: 55-59.

Stoller, E.W. and RA. Myers. 1989a. Response of soybean (Glycine max) and
four broadleaf weeds to reduced irradiance. Weed Sci. 37: 570-574.

Stoller, E.W. and RA. Myers. 1989b. Effects of shading and soybean interference
on eastern black nightshade growth and development. Weed Res. 29: 307-316.

Taylor, H.M., W.K. Mason, A.T.P. Bennie, and HR. Rowse. 1982. Response of
soybean to two row spacings and two soil water levels. I. An analysis of biomass

accumulation, canopy development, solar radiation interception, and components
of seed yield. Field Crops Res. 5: 1-14.

Young, B.G., J .M. Young, L.C. Gonzini, S.E. Hart, L.M. Wax, and G. Kapusta.

2001. Weed management in narrow- and wide-row glyphosate resistant soybean
(Glycine max). Weed Tech. 15: 112-121.

42

Figges

Figure 1. Cumulative eastern black nightshade emergence at East Lansing, MI in 2001.
LSD applies to total seasonal emergence at 90 days after planting.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LSD(pso_05)= NS
250
200 4’“— " " " " ' "
"E 1 a a 1
$ 150 I .——I I
Q . i
‘3 100 :—-—19-308 L,
g , +19432 L
50 - +76-308
. 41:41.32 ‘
O T I T i l 7 ' l
O 1 0 20 30 4O 50 60 70 8O 90 100
Days After Planting

Figure 2a. Cumulative eastern black nightshade emergence at East Lansing, MI in 2002.
LSD applies to total seasonal emergence at 90 days after planting.

 

1+76-185 _—-— 76-308 +76432 +19-308 +19432 +19-556 ;

 

 

LSD =NS

2

Plantsperm
Aawmwwe-A
momomomom

 

O

O 1 O 20 30 40 50 60 70 80
Days After Planting

43

Figure 2b. Cumulative eastern black nightshade emergence at Clarksville, MI in 2002.

LSD applies to total seasonal emergence at 90 days after planting.

 

 

 

[44—76-185 +76-308 +7643_2__+19-aoa 5519—432 + 193-553]

 

 

 

 

 

 

 

 

 

 

 

 

 

LSD =NS
14 (95005)
12
"E 10 //
I. I G i I
8. 8 fl ‘ c c : c s :
3 e
5 // Ff/
a 4
2 Jig!
o I I I I r I I
0 1O 20 30 40 50 60 70
Days After Planting

 

80

Figure 3. Soybean canopy development at East Lansing in 2001. Leaf area index (LAI)
was obtained by a non-destructive measurement using the SunScan Canopy Analysis

System (Delta-T Devices Ltd, Cambridge, England).

LSD=

0.25 NS

0.14 NS NS NS 053

Leaf Area Index

90 1 10
Days After Planting

50 70

44

NS NS

+ 19-308
+ 19-432
+ 76-308 '

; + 76432

 

130

150

Figure 4a. Soybean canopy development at East Lansing in 2002. Leaf area index (LAI)
was obtained by a non-destructive measurement using the SunScan Canopy Analysis
System (Delta-T Devices Ltd, Cambridge, England).

 

 

 

{+7e-185 +76-308 ...76-432 +19-308 4.419432 419-556“;

 

LSD=

_ 12 NS 0.69 0.54 1.44 2.17 ,_ 2.10, 0.30
11
10
X 9
'3 8

.E

a 7
2 6
:5 5
«a 4-
3 3
2
1
O

44 54 61 69 77 85 111

Days After Planting

Figure 4b. Soybean canopy development at Clarksville in 2002. Leaf area index (LAI)
was obtained by a non-destructive measurement using the SunScan Canopy Analysis
System (Delta-T Devices Ltd, Cambridge, England).

1+ 76-185 + 76-308 + 76-432_ + 19—308 + 19-432 + 19—556

 

 

 

 

LS D-
NS 1.27 1.48 1.24 NS 0.81

 

Leaf Area Index
0 —8 N 00 h 01 O) \1 on (D O

40 49 69 78 99 106
Days After Planting

45

Table 1. Monthly precipitation recorded at the Michigan State University Department of
Horticulture Teaching and Research Center, East Lansing, MI, and at the Clarksville

Horticulture Experiment Station in Clarksville, MI.

 

Precipitation (cm)

 

 

 

East Lansing Clarksville
2001 2002 30 yr. 2002 30 yr
May 14.5 12.1 6.9 10.4 7.4
June 8.5 5.4 8.9 6.6 4.7
July 2.4 9.5 7.6 4.7 6.0
Aug. 4.1 3.6 7.9 7.1 9.2
Total 25.4 30.6 31.3 28.8 32.2

 

46

Table 2. Eastern black nightshade density and dry weight per plant in October 2001 at

East Lansing as affected by soybean row spacing and plant population.“1

 

Soybean Plant Eastern Black Nightshade Eastern Black Nightshade

 

Population Density Dry Weight per Plant
(seed/ha) (plants/m2) (g)
19 cm
308 000 38 a 1.39 a
432000 30a 1.11 a
76 cm
308 000 33 a 1.92 a
432 000 35 a 1.09 a

 

aWithin column values followed by different lower case letters are statistically different

at or = 0.05.

47

Table 3. Eastern black nightshade density and dry weight per plant at Clarksville and East

Lansing as affected by soybean row spacing and plant population in October 2002.a

 

 

 

 

Eastern Black Nightshade Eastern Black Nightshade
Density Dry Weight Per Plant
East Lansing Clarksville East Lansing Clarksville
(plants per m2) (g)
19 cm
308 000 0 b 4 ab 0 b 0.86 b
432 000 0 b 4 ab 0 b 0.69 b
556 000 O b 2 b 0 b 0.45 b
76 cm
185000 4a 7a 1933 2.21 a
308 000 4 a 4 ab 1.04 ab 1.87 ab
432 000 5 a 3 b 0.61 ab 1.24 b

 

aWithin columns values followed by different lower case letters are significantly different

at or = 0.05.

48

Table 43. Eastern black nightshade density in microplots at East Lansing in 2002.a

 

Eastern Black Nightshade Density

 

 

Soybean Plant
Population (seed/ha) July 9 August 6 October 1
Plants per m2

19 cm
308 000 20 ab 15 b 2 b
432 000 15 b 15 b 2 b
556 000 16 b 14 b 0 b

76 cm
185 000 22 ab 24 a 13 a
308 000 25 a 22 a 13 a
432 000 21 ab 23 a 10 a

 

aWithin columns values followed by different lower case letters are significantly

different at a = 0.05.

49

Table 4b. Eastern black nightshade density in microplots at Clarksville in 2002.a

 

Eastern Black Nightshade Density

 

 

Soybean Plant
Population (seed/ha) July 9 August 6 October 1
Plants per m2

19 cm
308 000 12 ab 3 b 12 ab
432 000 5 ab 3 b 5 b
556 000 4 b 7 ab 9 ab

76 cm
185000 153 11ab 13 ab
308000 153 lOab 17a
432000 13 ab 14a 11 ab

 

aWithin columns values followed by different lower case letters are significantly

different at a = 0.10.

50

Table 5. 2002 eastern black nightshade dry weight per plant in microplots as affected by

soybean row spacings of 19- and 76-cm.a

 

 

 

 

 

Total dry weight
July 9 August 6 October 1
g

East Lansing

19 cm 0.07 b 0.15 b 0.01 a

76 cm 0.19 a 0.69 a 0.51 a
Clarksville

19 cm 0.09 b 0.17 b 0.40 b

76 cm 0.47a 1.14a 1.45 a

 

aWithin columns values followed by different lower case letters are significantly

different at or = 0.10.

51

Table 6. 2002 eastern black nightshade berry dry weight in microplots as affected by

soybean row spacings of 19- and 76-cm. 8

 

 

 

Berry Dry Weight
August 6 October 1
g

East Lansing

19 cm 0.00 a 0.00 a

76 cm 0.20 a 0.29 a
Clarksville

19cm 0.01 a 0.12b

76 cm 1.48 a 0.99 a

 

aWithin columns values followed by different lower case letters are significantly

different at 0. = 0.05.

52

Table 7a. Effect of soybean row Spacing, plant population, and eastern black nightshade

on microplot soybean yield at East Lansing in 2002.3 b

 

 

Soybean Yield (kg/ha)

Soybean Population

(seeds/ha) Untreated Glyphosate
19 cm

308 000 2441 AB(a) 2760 A(a)

432 000 2547 AB(a) 2547 A(a)

556 000 2208 B(a) 2356 A(a)
76 cm

185 000 2675 AB(a) 2654 A(a)

308 000 2314 AB(a) 2632 A(a)

432 000 2866 A(a) 2484 A(a)

 

aMean separation (LSDoos) between herbicide treatments within soybean row spacing
and population are denoted by lower case letters within parentheses.

bMean separation (LSDoos) within herbicide treatment are denoted by capital letters.

53

Table 7b. Effect of soybean row spacing, plant population and eastern black nightshade

on microplot soybean yield at Clarksville in 2002. a b

 

 

Soybean Yield (kg/ha)

Soybean Population

(seeds/ha) Untreated Glyphosate
19 cm

308 000 3267 A(a) 3028 B(a)

432 000 3249 A(a) 3285 AB(a)

556 000 3010 A(a) 3579 A(a)
76 cm

185 000 3341 A(a) 3348 AB(a)

308 000 3029 A(a) 3568 AB(a)

432 000 3194 A(a) 2980 B(a)

 

aMean separation (LSDoos) between herbicide treatments within soybean row spacing

and population are denoted by lower case letters within parentheses.

bMean separation (LSDoos) within herbicide treatment are denoted by capital letters.

54

Table 8. Effect of soybean row spacing, population and herbicide treatment on soybean

yields at East Lansing in 2001. a b

 

 

 

Soybean Yield (kg/ha)

Soybean Plant Glyphosate
Population (seeds/ha) Untreated Glyphosate + Irnazethapyr
19 cm

308 000 3030 A(a) 3426 A(a) 3174 A(a)

432 000 3215 A(a) 3263 A(a) 3618 A(a)
76 cm

308 000 3284 A(a) 3231 A(a) 3092 A(a)

432 000 3027 A(b) 3769 A(a) 3125 A(b)

 

aMean separation (LSDOJ) between herbicide treatments within soybean row spacing and

population are denoted by lower case letters within parentheses.

bMean separation (LSD0_1) within herbicide treatment are denoted by capital letters.

55

Table 93. Effect of soybean row spacing, population, and herbicide treatment on soybean

main plot yield at East Lansing in 2002. a b

 

 

 

Soybean Yield (kg/ha)
Soybean Population Glyphosate
(seeds/ha) Untreated Glyphosate + Imazethapyr
19 cm
308 000 3490 A(a) 3544 A(a) 3526 A(a)
432 000 3524 A(a) 3652 A(a) 3319 A(a)
556 000 3396 AB(a) 3517 A(a) 3601 A(a)
76 cm
185 000 3040 B(a) 3376 A(a) 3245 A(a)
308 000 3295 AB(a) 3416 A(a) 3547 A(a)
432 000 3551 A(b) 3968 A(a) 3415 A(b)

 

aMean separation (LSDQI) between herbicide treatments within soybean row spacing and

population are denoted by lower case letters within parentheses.

bMean separation (LSDm) within herbicide treatment are denoted by capital letters.

56

Table 9b. Effect of soybean row spacing, plant population and herbicide treatment on

soybean main plot yield at Clarksville in 2002. a b

 

Soybean Yield (kg/ha)

 

Soybean Plant Glyphosate

Population (seeds/ha) Untreated Glyphosate + Imazethapyr

 

19 cm
308 000 3228 BC(b) 3773 A(a) 3411 B(b)
432 000 3558 A(a) 3403 B(a) 3440 B(a)
556 000 3537 A(b) 3753 A(a) 3626 A(ab)
76 cm
185 000 3120 B(b) 3450 B(a) 3299 B(ab)
308 000 3349 B(a) 3336 B(a) 3342 B(a)
432 000 3443 A(ab) 3618 A(a) 3386 B(b)

 

aMean separation (LSDO_|) between herbicide treatments within soybean row spacing and
population are denoted by lower case letters within parentheses.

bMean separation (LSDOJ) within herbicide treatment are denoted by capital letters.

57

CHAPTER 3

THE INFLUENCE OF LIGHT QUANTITY AND QUALITY ON THE
EMERGENCE AND GROWTH OF EASTERN BLACK NIGHTSHADE (Solanum
ptycanthum) AND HAIRY NIGHTSHADE (Solanum sarrachoides).
Abstract. Growth chamber and greenhouse experiments were conducted to determine the

effect of light quantity and quality on the germination and growth of eastern black
nightshade and hairy nightshade. The germination of eastern black nightshade was not
significantly reduced regardless of shade level. Hairy nightshade germination was
reduced by an irradiance level of 46 uE/mZ/sec compared to 146 pE/mZ/sec. Leaf,
reproductive, and total dry weight of eastern black nightshade and hairy nightshade was
reduced in light levels of 63 uE/mz/sec compared to full greenhouse light. Eastern black
nightshade and hairy nightshade had similar leaf areas in full greenhouse light, however,
eastern black nightshade leaf area did not decrease as the available irradiance decreased.
Both hairy and eastern black nightshade adapt to a shaded environment by producing
thinner leaves and increasing their leaf surface area. The leaf, reproductive and total dry
weight of both nightshade species was greater under full greenhouse light compared to
plants grown under neutral and reduced red: far red shade treatments. The specific leaf
area of eastern black nightshade and hairy nightshade was greater under the neutral
density shading compared to full greenhouse light and reduced R: FR treatments,
indicating a blue-absorbing pigment response. Eastern black and hairy nightshade grth
and reproduction were reduced when grown under irradiances of 63 and 51 uE/mz/ sec,

indicating that narrowing soybean row spacing and increasing plant population will also

reduce the growth and reproduction of these shade tolerant species.

58

KEY WORDS: Light quality, light quantity, eastern black nightshade (Solanum

ptycanthum), hairy nightshade (Solanum sarrachoides).

INTRODUCTION

Shade effectively inhibits the growth of many weeds because of the reduction in
irradiance. Crops and weeds Show varying degrees of Shade tolerance. Eastern black
nightshade, tumble pi gweed, and common cocklebur were photosynthetically efficient
under low- growth irradiance due to a combination of physiological and morphological
adaptations (Holt, 1995; Regnier et a1, 1988; Stoller and Myers, 1989). Hairy nightshade,
another nightshade species that is common in Michigan, did not persist in dense shades
(Tan and Weaver, 1997). Increased leaf area ratio (LAR) and plant height are common
responses to shade that may offset reductions in photosynthetic rate and biomass
production that commonly occur. However, seed production is generally reduced when
reductions in light are extreme (Holt, 1995). Eastern black nightshade can be a problem
in soybean fields because seedlings can emerge from sites receiving firll sunlight between
soybean rows, and they can also emerge from heavily Shaded sites beneath the soybean
canopy. Furthermore, eastern black nightshade can grow under the soybean canopy
where irradiance levels are less than 100 uE/mz/s (Stoller and Myers, 1989a). Nightshade
growth and berry production are greatly reduced once the soybean canopy begins to
close, but the ability of eastern black nightshade to survive beneath a soybean canopy
creates the potential for eastern black nightshade to be problematic throughout the

growing season.

59

Sporadic seed germination is a common trait in black nightshade, which enables
nightshade seedlings to emerge throughout the growing season (Keely and Thullen,
1983). Nightshade began to germinate in the spring and emergence continued throughout
the summer when adequate moisture was available in Washington, Canada, and England
(Ogg and Dawson, 1984; Roberts and Boddrell, 1983; Basset and Munro, 1985; Roberts
and Lockett, 1978). Roberts and Lockett reported that black nightshade seeds failed to
germinate at constant temperatures in the range of 4-30°C; however, with alternating
temperatures of 10/25, 10/30, 15/25 and 15/30 the percent germination was high (Roberts
and Lockett, 1978). The most rapid and complete germination occurred when the upper
temperature was 25 to 30°C. Hairy and eastern black nightshade seeds germinated in the
field when soil temperatures were between 20° and 46° C. The optimum temperature for
germination of eastern black nightshade and hairy nightshade was 30° C (Bugert et a1,

1 973).

The presence of a leaf canopy alters the quantity as well as the spectral
distribution, or quality, of light underneath it. Leaves absorb light in the blue and red
regions and reflect or transmit in the green and far red regions of the spectrum. With
increasing depth in a plant canopy, light is enriched in the far red wavelengths and has a
lower red:far red ratio (Smith, 1994). The morphological responses seen by plants in
response to reduced irradiance, such as increased leaf area ratio (LAR), are triggered by
phytochrome in response to the low red: far red ratios under plant canopies (Taiz and
Zieger,2002). These morphological responses include stem elongation, flowering, and

changes in stomatal conductance or plant anatomy. Leaf thinning in shaded conditions

60

has also been attributed to an increase in the ratio of R: FR light, but may also result from
a decrease of blue light.

Weed success depends on survival and some level of reproduction to continue the
species. Knowledge of the responses of hairy nightshade and eastern black nightshade to
different levels of light quantity and quality will allow for the development of
management techniques to enhance control of these two weed species. The objectives of
this experiment were to determine the effect of light quantity and quality on the
germination and grth of eastern black nightshade and hairy nightshade. We
hypothesize that shading will have no effect on the germination of either nightshade
species. Secondly, we hypothesize that eastern black nightshade will have greater
biomass and leaf area compared to hairy nightshade when grown under neutral shade
levels of 30%, 60%, and 90%; however both species of nightshade will have optimum
biomass and leaf area when light interception is not reduced. Furthermore, we
hypothesize that reduced red: far red light will result in greater leaf area of nightshade

species compared to leaf area neutral light.

61

MATERIALS AND METHODS

The effect of neutral density shading on germination of eastern black nightshade
and hairy nightshade.

Seed was collected in the fall of 2000 from a population of hairy nightshade and
eastern black nightshade growing in farmer’s fields in Michigan. Hairy nightshade was
collected in Presque Isle Country and eastern black nightshade berries were collected in
Ingham County. Berries were air dried and seed removed by crushing the berries. Seed
was then separated from the inert matter by sieving. The seeds were washed with water to
remove any seed inhibitors and air dried on aluminum foil. Preliminary germination
studies were conducted. Twenty-five seeds of eastern black nightshade and hairy
nightshade were placed in a seed gerrninator at varying alternating temperatures of 20:10,
25:15, 25:25, 30:20, and 35:25 degrees C. It was shown that the optimum temperature for
germination of both species was 30:20 C with a 14 hr photoperiod. These results are
similar to that found previously in the literature (Bugert et al. 1973, Givelberg and
Horowitz 1984, Roberts and Lockett 1978, and Thomson and Witt 1987). Sixteen pots
were seeded with each Species of nightshade. Twenty nightshade seeds were placed at a 1
cm depth in the soil in each pot. The soil used was a Spinks loamy sand (sandy mixed,
mesic Psarnmentic Hapludalfs) with a pH of 6.8 and 2.4% organic matter. The seed was
evenly distributed throughout the pot and the pots were placed in the growth chamber
under 30°: 20°C with 14 hour daylight. Dark shade cloth rated for solar radiation
interception of approximately 30%, 60%, and 90% was placed over four pots of each
species at planting. Irradiance levels beneath this cloth was of 146, 46 and 32 uE/mZ/sec,
denoting an actual 42%, 82%, and 87% reduction in light quantity. The other four pots of

each species were the control with no shade cloth with an irradiance level of 255

62

uE/mz/sec. Photosynthetic photon flux density G’PF D) was measured for each light level
using a recently calibrated LI-COR LI-185B1 quantum sensor. Shade structures were
arranged to rrrininrize any shading of one particular treatment by another. Pots were
watered each day as needed and pots were evaluated every three days for nightshade
emergence. Nightshade was clipped at the soil line at the cotyledon stage to prohibit
potential shading of the soil. Pots were rotated within shade level weekly. The
experiment was terminated after 3 weeks and repeated. The experiment was a two factor
factorial with nightshade species as one factor and light level as the second factor and
was arranged in a completely randomized design with four replications. An analysis of
variance was conducted using PROC GLM in SAS and experiments were combined over
time. Means were separated with Fisher’s LSD at the 5% level.

The effect of light quality and quantity on the growth of eastern black nightshade
and hairy nightshade.

Thirty pots were seeded with pro-germinated eastern black nightshade and hairy
nightshade seed. Five pro-germinated seeds were placed at a 1 cm depth in the soil in
each pot. Pots were placed in the greenhouse under 27 i 5 degrees Celsius and 14 hr of
natural daylight supplemented by sodium vapor lighting with a PPFD of 120 (E m'2 - 5".
Dark shade cloth rated for solar radiation interception of approximately 30%, 60%, and
90%, and shade cloth with reduced red:far red light with a radiation interception Similar
to the 60% dark shade was placed over six pots of each species at planting. The other six
pots of each species were the control with no shade cloth. Irradiance levels corresponded
to 195, 63 and 51 pE/mz/sec for the dark shade cloth, 68 uE/mz/sec for the reduced red:

far red shade, and 292 uE/mZ/sec for the control, denoting a 33%, 78%, 82%, and 77%

 

' Ll-COR, 4421 Superior Street, PO. Box 4425, Lincoln, NE 68504.

63

actual reduction in light quantity. PPFD was measured at approximately solar noon on a
clear day within each shade level using a recently calibrated LI-COR LI-185B1 quantum
sensor. Spectral emission beneath each shade level over the range of 300 to 1100 nm was
determined using a LI-COR 1800l portable spectral radiometer. The amount of red: far
red light was then calculated by the following formula as described by Kendrick and
Kronenberg (1994) :

R: FR: Photon irradiance between 655 and 665 nm

 

Photon irradiance between 725 and 735 nm
Shade structures were 2.5 feet tall and 1.5 feet wide and arranged to minimize any
shading of one particular treatment by another. Pots were watered each day as needed
and fertilized with 3 g of water soluble fertilizer (20% N, 20% P202, and 20% K20) per
gallon of water and pots were re-randomized on a weekly basis under each shade
treatment. Nightshade was thinned to one plant per pot when the plants were at the six
leaf stage. The plants were evaluated bi-weekly beginning 14 d after planting by
recording the growth stage of each plant in each pot. Leaf area, fresh weight and dry
weight of leaves and total biomass were measured destructively 8 weeks after planting.
Specific leaf area (SLA) was calculated by dividing leaf area by leaf dry weight (Kvert et
al. 1971). Leaf area was measured using a LI-COR LI 3000l portable area meter. The
experiment was a two-factor factorial with nightshade species as one factor and light
level as the second factor arranged in a completely randomized design with four
replications and repeated. An analysis of variance was conducted using PROC GLM in

SAS and experiments were combined over time. Means were separated with Fisher’s

LSD at the 5% level.

64

RESULTS AND DISCUSSION

The effect of neutral density shading on germination of eastern black nightshade
and hairy nightshade.

The maximum emergence of eastern black nightshade and hairy nightshade was
20% and 34%, respectively (Table 1). Thompson and Witt (1987) reported 72%
germination of eastern black nightshade under similar conditions. It has been reported
that germination of dry stored nightshade seeds is promoted by gibberellic acid (Basset
and Munro 1985, Givelberg and Horowitz 1984, and Roberts and Lockett 1978).
Dormant seeds of hairy nightshade germinated 50% or more after soaking for 12 h in 2.8
x 10*3 M gibberellic acid and incubating for several days at 20/30 C (Givelberg and
Horowitz 1984). The nightshade seed in this study was not treated with gibberellic acid,
which may account for the low percentage of germination.

The germination of eastern black nightshade was not significantly reduced,
regardless of shade level (Table 1). However, hairy nightshade germination was reduced
by an irradiance level of 46 uE/mz/sec compared to the 146 pE/mz/sec (p = 0.0018).
When both species were compared within a shade treatment, hairy nightshade had
significantly greater emergence in 146 uE/mz/sec (p = .0032) and 46 uE/mZ/sec (p =
0.0430) shade treatments compared to eastern black nightshade. These results imply that
our seed source of hairy nightshade had greater germination at two of four shade levels
compared to eastern black nightshade, and that our dry storage conditions were not
conducive for germination. Furtherore, this seed source of hairy nightshade had
decreased seed germination under conditions of low irradiance. Seed germination can be

influenced by the environment at the time of seed formation by seed position on the plant

65

and by post harvest seed handling (Rogers and Ogg 1989). It would be of interest to
compare seeds from the same field to determine if hairy nightshade germination is
reduced in low irradiance.
The effect of light quality and quantity on the growth of eastern black nightshade
and hairy nightshade.
Light Quantity
Leaf (p = <.0001), reproductive (p =<.0001) and total dry weight (p =<.0001) of eastern
black nightshade and hairy nightshade was significantly reduced in light levels of 63
uE/mz/sec and 5 l uE/mZ/sec compared to full greenhouse light (Table 2). Hairy
nightshade reproductive dry weight was also reduced (p=.007) by an irradiance of 195
uE/mz/sec compared to full greenhouse light. The leaf area of eastern black nightshade
was greater than the leaf area of hairy nightshade at all reduced irradiance levels, but not
under full greenhouse light. Furthermore, the leaf area of hairy nightshade, but not
eastern black nightshade, was reduced at an irradiance of 51 uE/mZ/sec (p = .0042)
compared to full greenhouse light. These results indicate that eastern black nightshade
and hairy nightshade have similar leaf areas at 292 uE/mz/sec and that eastern black
nightshade leaf area did not decrease as the available irradiance decreased. Stoller and
Myers (1989a) reported that eastern black nightshade had the highest leaf area ratio
(LAR) compared to three other weed species tested in shaded conditions.

Eastern black nightshade and hairy nightshade had greater specific leaf area
(SLA) under irradiances of 63 and 51 uE/mZ/sec when compared to plants grown in full
greenhouse light or beneath an irradiance of 195 uE/mz/sec. The greater SLA of plants

grown under Shade shows a common adaptation of shade-avoiding plants, namely thinner

66

leaves. Other research supports greater SLA for shade-intolerant weeds grown under
neutrally filtered radiation (Regnier and Harrison 1993; Crotser and Witt 2003),
indicating that the thinner leaves optimize leaf surface area and chlorophyll exposure to
light. Blackshaw (1991) reported that hairy nightshade does not persist in dense shade,
although it is able to compete for light in widely spaced row crops. Our data suggest that
hairy nightshade is also able to adapt to a shaded environment by producing thinner
leaves and increasing the leaf surface area to optimize the available light.
Light Quality

The leaf, reproductive, and total dry weight of both nightshade species was
greater in the no shade treatment compared to plants grown under both neutral and
reduced R: FR shade treatments. Additionally, the leaf and total dry weight of both
nightshade species grown under reduced red: far red (R: FR) shade with a light quantity
of 68 uE/mZ/sec was greater than the leaf dry weight of plants grown under neutral
density shade with a light quantity of 63 uE/mz/sec (Table 3). Although the plant weights
were greater in the no shade treatment, the leaf area of eastern black nightshade was
greater beneath the reduced R: FR shade compared to neutral density shade and full sun.
The leaf area of hairy nightshade was greater in the no shade compared to the neutral
density treatment. When the SLA was calculated, the SLA of eastern black nightshade
and hairy nightshade was greater under the neutral density shading. A possible
explanation for this could be that the response of thinner leaves seen in nightshade plants
grown under neutral density shade was caused by blue-absorbing pigments instead of
phytochrome. Brits and Sager (1990), reported that at equal PPF D, soybean and sorghum

(Sorghum bicolor L.) leaves were thinner when plants were grown under blue deficient

67

lamps (low pressure sodium) when compared with broad-spectrum daylight fluorescent
lamps. This suggests that reduced irradiance, specifically blue light, inhibited the
development of thick leaves in eastern black nightshade and hairy nightshade, since
thinner leaves occurred only at neutral shade density and not in the reduced R: FR shade
treatment.

Red to far red ratios were measured as 1.11, 1.07, and 0.98 for plants grown under
full sun, neutral, and reduced R: FR shade, respectively. In full sunlight, there is a R: FR
ratio of approximately 1.10 and a soybean canopy will typically have a R: FR ratio of
0.14 (Smith, 1994). Therefore, although the red to far red ratio was reduced somewhat
with the green shade cloth, the reduction in R: FR light was minimal for our study.
Consequently, the differences in growth between the two shade treatments may be
explained by differences in the microclimate beneath the two shade treatments. Although
both the neutral density cloth and the reduced R: FR cloth were rated for 60% shade, the
reduced R: FR cloth allowed 1.7% more light (68 uE/mZ/sec) to be available for plant
growth compared to the neutral density cloth (63 uE/mz/sec). Therefore, irradiance was
increased very slightly under the green compared to the black shade cloth treatment. Of
more importance was the daily maximum temperature beneath the shade structures. The
daily temperature maximums beneath the reduced R: FR shade cloth was approximately
5° C warmer than that of the neutral density shading on days with firll sun (Figure 1). On
cloudy days, the temperature was similar between both shade treatments, although still
slightly elevated under the reduced R: FR compared to the neutral shade. The increase in
temperature in the green shade cloth allowed the nightshade plants under the reduced R:

FR cloth to produce more biomass than those growing beneath the neutral density shade.

68

In conclusion, the leaf, reproductive, and total dry weight of eastern black
nightshade and hairy nightshade decreased as light quantity and the ratio of red to far-red
light decreased. Under natural conditions, full sunlight would have an irradiance level of
approximately 2000 uE/mZ/sec. Full light in the greenhouse conditions in this study
measured 292 uE/mz/sec. This is a shaded environment in comparison to field conditions;
therefore, plants grown in the full greenhouse light treatment may have also shown some
effects due to shading.

The leaf area of eastern black nightshade was only reduced under neutral density
Shading at an irradiance of 32 uE/mZ/sec. The leaf area of hairy nightshade was reduced
under both neutral and reduced R: FR light with irradiances of 63 and 68 uE/mz/sec,
respectively. Reproductive dry weight for eastern black nightshade and hairy nightshade
was reduced by 89% when light quantity was reduced by 82% compared to full
greenhouse light. The SLA of eastern black nightshade and hairy nightshade was greatest
under irradiances of 63 and 51 uE/mz/sec beneath neutral density shade compared to that
of reduced R: FR shade and full greenhouse light, indicating a blue pigment response.

The grth and reproduction of both hairy nightshade and eastern black
nightshade decreased when grown in shade. The compensatory responses of eastern black
nightshade to shade, by maximizing interception of available light, allows eastern black
nightshade to maintain growth under shaded conditions. However, eastern black
nightshade grth and reproduction were reduced when grown under irradiances of 63
and 51 uE/mZ/sec, indicating that narrowing soybean row spacing and increasing plant
population will also reduce the growth and reproduction of this shade tolerant species.

Hairy nightshade is also able to adapt to a shaded environment by producing thinner

69

leaves and increasing the leaf surface area to optimize the available light, allowing it to
be more competitive in wide spaced crops. However, at high levels of Shade, hairy
nightshade growth and reproduction is also reduced, indicating that narrowing crop rows
and increasing plant population will also reduced the growth and reproduction of hairy

nightshade.

7O

Table 1. Effect of neutral shading on the cumulative emergence of eastern black

nightshade and hairy nightshade.a

 

 

 

 

Light Eastern Black Nightshade Hairy Nightshade
Quantity

uE/mZ/sec — Number Emerged out of 20 seeds —

32 3.2 c 4.4 Do

46 3.8 c 6.3 ab

146 4.7 be 8.4 a

255 5.0 be 6.7 ab

 

aTreatment means within a column followed by the same letter are not statistically

different at the 5% level.

bTreatment means within a row followed by the same letter are not statistically different

at the 5% level.

71

Table 2. Effects of neutral shading on the reproductive, stern, leaf, and total dry weight,

leaf area, and specific leaf area of eastern black nightshade and hairy nightshade“.

 

 

 

 

Light
Quantity Leaf Dry Reproductive Total Dry Leaf Specific
pE/mz/sec Weight Dry Weight Weight Area Leaf Area*
g —cm2_ _ cm g’I_
Eastern Black
Nightshade
51 0.60 cd 0.03 c 0.93 b 690.08 bc 1190.60 a
63 1.15 c 0.09 c 1.65 b 867.75 ab 937.62 a
195 2.75 ab 0.71 ab 4.88 a 1001.75 a 394.54 b
292 2.96 a 1.04 a 5.63 a 821.67 ab 309.04 b
Hairy
Nightshade
51 0.27 d 0.00 c 0.44 b 248.00 (1 943.77 a
63 0.62 cd 0.01 c 0.97 b 459.33 cd 921.32 a
195 2.23 b 0.43 b 4.26 a 775.25 bc 367.52 b
292 2.52 ab 0.90 a 5.46 a 713.5 bc 305.28 b

 

aTreatment means within a column and followed by the same letter are not significantly

different at the 5% level.

*Specific leaf area was calculated by dividing leaf area by leaf dry weight.

72

Table 3. Comparison of radiation quality on the reproductive, stem, leaf, total dry weight,

leaf area and specific leaf area of eastern black nightshade and hairy nightshade.

 

 

 

 

Shade Leaf Dry Reproductive Total Dry Leaf Specific
Treatment Weight“l Dry Weight“ Weight“ Area“ Leaf Area*
3 — cm2_ _ cm g'l _

Eastern Black
Nightshade
No Shade 1.70 a 0.46 a 4.23 a 962.27 b 709.48 bc
Neutral density 0.17 c 0.01 b 0.60 c 393.38 (1 2364.59 a
Reduced R: FR 1.09 b 0.11 b 3.13 a 1254.89 a 1191.98 bc
Hairy
Nightshade
No Shade 1.78 a 0.18 a 3.92 a 794.36 bc 509.16 c
Neutral Density 0.11 c 0.01 b 0.32 c 145.23 (1 1371.31 b
Reduced R: FR 0.76 b 0.01 b 1.80 b 677.65 c 893.09 bc

 

“Treatment means within a column and followed by the same letter are not significantly

different at the 5% level.

*Specific leaf area was calculated by dividing leaf area by leaf dry weight.

73

Figure 1. Temperature differences in greenhouse due to shade treatment. Daily maximum

(max) and minimum (min) temperatures for no shade (NS), neutral density (BL) and

reduced red: far red (GR) shade.

 

 

+ NS-max + NS-min f- BL-max JBL-min—o— GR—max —4— 63-min?

(flak->01
OU‘IOO'IO

Temperature (C)
N N
o 01

 

4.x
OUTCC’I

17-Apr 18-Apr 19-Apr 20-Apr 21-Apr 22-Apr 23-Apr
Date

74

10.

ll.

12.

LITERATURE CITED

. Bassett, I.J., and DB. Munro. 1985. The biology of Canadian Weeds. 67.

Solanum ptycanthum Dun., S. nigrum L., and S. sarrachoides Sendt. Can. J. Plant
Sci. 65: 401-414.

Brits, SJ and J .C. Sager. 1990. Photomorphogenic and photoassimilation in
soybean and sorghum under broad spectrum or blue-deficient light sources. Plant
Physiol. 94: 448-454.

Bugert, KL. and 0C. Burnside. 1972. Optimum temperature for germination and
seedling development of black nightshade. Res. Rep., North Cent. Weed Control
Conf. 29: 56-57.

Crotser, MP. and W.W. Witt. 2003. Neutral density shading and far-red radiation
influence black nightshade (Solanum nigrum) and eastern black nightshade
(Solanum ptycanthum) growth. Weed Sci. 51: 208-213.

Givelberg, A. and M. Horowitz. 1984. Germination behavior of Solanum nigrum
seeds. J. Exp. Bot. 35: 588-598.

Holt, J .S. 1995. Plant responses to light: A potential tool for weed management.
Weed Sci. 43: 474—482.

Keely, PE. and R.J. Thullen. 1983. Influence of planting date on the growth of
black nightshade. Weed Sci. 31: 180-184.

Kvet, J ., R. Ondok, J. Necas, and PG. Jarvis. 1971. Methods of growth analysis.
Pages 347-356 in J. Catsky and PC. Jarvis, eds. Plant Photosynthetic Production.
Manuels and Methods. The Hague, The Netherlands: W. Junk.

Ogg, A.G., Jr., and J .A. Dawson. 1984. Time of emergence of eight weed species.
Weed Sci. 32: 327-335.

Regnier, BE. and K. Harrison. 1993. Compensatory response of common
cocklebur (Xanthium strumarium) and velvetleaf (Abutilon theophrasti) to partial
shading. Weed Sci. 41: 541-547.

Regnier, BE, ME. Salvucci, and E.W. Stoller. 1988. Photosynthesis and growth
response to irradiance in soybean (Glycine max) and three broadleaf weeds. Weed
Sci. 36: 487-496.

Roberts, HA, and J .E. Boddrell. 1983. Field experiments and temperature

requirements for germination in Solanum sarrachoides Sendt. Weed Res. 23: 247-
252.

75

13.

14.

15.

l6.

l7.

l8.

19.

Roberts, HA, and RM. Lockett. 1978. Seed dormancy and field emergence in
Solanum nigrum L. Weed Res. 18: 231-241.

Rogers, BS. and AG. Ogg, Jr. 1989. Taxonomy, Distribution, Biology, and
Control of Black Nightshade (Solanum nigrum) and related species in the United
States and Canada. Rev. Weed Sci. 4: 25-58.

Smith, Harry. 1994. Sensing the Light Environment. p. 377 - 416 in R. E.
Kendrick & G. H. M. Kronenberg (eds), Photomorphogenesis in Plants- 2nd

Edition. Kluwer Academic Publishers, Printed in the Netherlands.

Stoller, E.W. and RA. Myers. 1989a. Response of soybeans (Glycine max) and
four broadleaf weeds to reduced irradiance. Weed Sci. 37: 570-574.

Stoller, E.W. and RA. Myers. 1989b. Effects of shading and soybean interference
on eastern black nightshade grth and development. Weed Res. 29: 307-316.

Tan, CS, and SE. Weaver. 1997. Water use patterns of eastern black nightshade
(Solanum ptycanthum) and hairy nightshade (Solanum sarrachoides) in response

to shading and water stress. Can. J. Plant Sci. 77: 261-265.

Taiz, L. and E. Zieger. 2002. Plant Physiology, Third Edition. p.376-417.

76

APPENDICES

CHAPTER TWO ANOVA TABLES

Figure 1. Cumulative emergence of eastern black nightshade at East Lansing 2001.

Effect Num DF Den DF F Value P Value
Blk 3 3 0.95 0.5149
Row 1 3 0.02 0.9005
Pop 1 6 0.35 0.5774
Row*Pop 1 6 0.25 0.6360

Figure 2. Cumulative emergence of eastern black nightshade at East Lansing in 2002.

Effect Num DF Den DF F Value P Value
Blk 1 3 0.22 0.6692
Row 2 12 1.38 0.2889
Pop 3 3 1.16 0.4517
Row*Pop 2 12 3.0 0.0879

Figure 2b. Cumulative emergence eastern black nightshade at Clarksville 2002.

Effect Num DF Den DF F Value P Value
Row 1 3 0.51 0.5261
Pop 2 12 0.1 1 0.8966
Blk 3 3 2.40 0.2457

Row*Pop 2 12 0.33 0.7249

77

Figure 3. Soybean Canopy Development at East Lansing 2001.

52 DAP
Effect
Blk
Row
Pop
Row*Pop
60 DAP
Effect
Blk
Row
Pop
Row*Pop
67 DAP
Effect
Blk
Row
Pop
Row*Pop
81 DAP
Effect
Blk

Row

Num DF

Num DF

Num DF

Num DF

Den DF

20

20

Den DF

54

54

Den DF

11

11

Den DF

78

F Value

0.01

10.71

6.26

.39

F Value

2.25

13.80

5.87

0.65

F Value

0.28

0.02

7.11

1.09

F Value

1.29

0.22

P Value

0.9980

0.0467

0.0211

0.5370

P Value

0.2611

0.0339

0.0188

0.4230

P Value

0.8372

0.9082

0.0219

0.3188

P Value

0.4651

0.6857

Pop
Row*Pop
91 DAP
Effect
Blk
Row
Pop
Row*Pop
105 DAP
Effect
Blk
Row
Pop
Row*Pop
112 DAP
Effect
Blk
Row
Pop
Row*Pop
119 DAP
Effect

Blk

Num DF

Num DF

Num DF

Num DF

Den DF

54

54

Den DF

54

54

Den DF

54

54

Den DF

79

4.03

0.27

F Value

0.59

0.87

1.26

0.01

F Value

2.88

15.87

0.29

0.09

F Value

0.69

0.70

0.45

0.13

F Value

0.66

0.1011

0.6235

P Value

0.6617

0.4206

0.2657

0.9298

P Value

0.2042

0.0283

0.5923

0.7630

P Value

0.6148

0.4648

0.5064

0.7227

P Value

0.6281

Row
Pop

Row*Pop

139 DAP
Effect
Blk
Row
Pop

Row*Pop

Num DF

3

1

l

1

54

54

Den DF

3

3

54

54

3.57

0.43

1.65

F Value

0.76

1.97

0.47

0.20

Figure 4a. Soybean Canopy Development at East Lansing 2002.

44 DAP
Effect
Blk
Row
Pop
Row*Pop
54 DAP
Effect
Blk
Row
Pop

Row*Pop

Num DF

Num DF

Den DF

15

15

15

15

Den DF

80

F Value

0.01

0.04

4.54

1.57

F Value

0.57

0.68

3.0

1.82

0.1554

0.5150

0.2038

P Value

0.5872

0.2551

0.4982

0.6554

P Value

0.9986

0.8372

0.0186

0.2290

P Value

0.6576

0.4400

0.1172

0.2261

61 DAP
Effect
Blk
Row
Pop
Row*Pop
69 DAP
Effect
Blk
Row
Pop
Row*Pop
77 DAP
Effect
Blk
Row
Pop
Row*P0p
85 DAP
Effect
Blk
Row

Pop

Num DF

3

1

Num DF

3

l

Num DF

3

l

Num DF

3

l

3

Den DF

15

15

15

15

Den DF

15

15

15

15

Den DF

15

15

15

15

Den DF

15

15

15

81

F Value

0.43

3.0

4.11

0.12

F Value

0.07

22.43

2.41

0.15

F Value

1.49

11.56

1.75

0.24

F Value

0.90

0.30

1.60

P Value

0.7337

0.1037

0.0259

0.7338

P Value

0.9752

0.0003

0.1076

0.7002

P Value

0.2564

0.0040

0.1998

0.6342

P Value

0.4653

0.5890

0.2320

Row*P0p
l l 1 DAP
Effect
Blk
Row
Pop

Row*Pop

Num DF

3

1

3

1

15

Den DF

14

14

14

14

0.01

F Value

2.33

1.17

5.22

0.18

Figure 4b. Soybean Canopy Development at Clarksville 2002.

40 DAP
Effect
Blk
Row
Pop
Row*Pop
49 DAP
Effect
Blk
Row
Pop
Row*Pop
69 DAP
Effect

Blk

Num DF

Num DF

Num DF

Den DF

14

14

14

14

Den DF

Den DF

15

82

F Value

0.63

1.34

1.51

0.09

F Value

0.56

10.28

0.75

0.16

F Value

0.81

0.9189

P Value

0.1181

0.2973

0.0126

0.6742

P Value

0.6072

0.2661

0.2547

0.7651

P Value

0.6097

0.0327

0.5748

0.7069

P Value

0.5083

Row
Pop
Row*Pop
78 DAP
Effect
Blk
Row
Pop
Row*Pop
99 DAP
Effect
Blk
Row
Pop
Row*Pop
106 DAP
Effect
Blk
Row
Pop

Row*Pop

Num DF

Num DF

Num DF

15

15

15

Den DF

15

15

15

15

Den DF

15

15

15

15

Den DF

15

15

15

15

83

28.15

2.02

0.23

F Value

1.96

5.02

4.90

0.01

F Value

1.11

0.59

0.40

0.05

F Value

2.13

0.26

1.76

0.18

<0.0001

0.1537

0.6365

P Value

0.1638

0.0406

0.0143

0.9052

P Value

0.3771

0.4535

0.7581

0.8289

P Value

0.1394

0.6163

0.1973

0.6814

Table 2. Eastern black nightshade density and dry weight per plant at East Lansing in

October 2001.
Density
Effect Num DF Den DF F Value P Value
Blk 3 3 1.32 0.1394
Row 1 3 0.00 1.000
Pop 1 6 0.26 0.6265
Row*Pop 1 6 0.67 0.4435
Dry Weight Per Plant
Effect Num DF Den DF F Value P Value
Blk 3 3 1.52 0.3701
Row 1 3 0.00 0.9534
Pop 1 6 1 .86 0.2218
Row*Pop 1 6 0.00 0.9869

Table 3. Eastern black nightshade density and dry weight per plant at East Lansing and

Clarksville in October 2002.

East Lansing Density
Effect Num DF Den DF F Value P Value
Blk 3 3 1.00 0.5000
Row 1 3 12.45 0.0387
Pop 2 12 0.38 0.6907
Row*Pop 2 12 0.38 0.6907

84

East Lansing Dry Weight Per Plant

Effect
Blk
Row
Pop
Row*Pop
Clarksville Density
Effect
Blk
Row
Pop

Row*Pop

Num DF

3

l

Num DF

3

1

2

2

Clarksville Dry Weight Per Plant

Effect
Blk
Row
Pop

Row*Pop

Num DF

3

1

2

2

Den DF

12

12

Den DF

12

12

Den DF

3

3

12

12

F Value

1.00

6.55

2.09

2.09

F Value

0.36

2.58

3.14

0.91

F Value

1.32

10.64

9.06

1.51

P Value

0.5000

0.0833

0.1659

0.1659

P Value

0.7905

0.2064

0.0800

0.4283

P Value

0.4130

0.0471

0.0040

0.2600

Table 4a. Eastern black nightshade density in microplots at East Lansing in 2002.

July Density
Effect
Blk

Row

Num DF

3

l

Den DF

3

3

85

F Value

0.52

2.80

P Value

0.6954

0.1931

Pop
Row*Pop
August Density
Effect
Blk
Row
Pop
Row*Pop
October Density
Effect
Blk
Row
Pop

Row*Pop

Num DF

Num DF

2

Den DF

Den DF

3

3

12

12

2.14

0.04

F Value

1.27

5.14

0.00

0.19

F Value

2.38

22.15

1.68

0.09

0.1938

0.8413

P Value

0.4235

0.1081

1 .0000

0.6754

P Value

0.2470

0.0181

0.2280

0.9161

Table 4b. Eastern black nightshade density in Microplots at Clarksville in 2002.

July Density
Effect
Blk
Row
Pop

Row*Pop

Num DF

Den DF

3

3

86

F Value

1.27

1.22

0.93

0.17

P Value

0.4255

0.3508

0.3720

0.6937

August Density

Effect Num DF
Blk 3
Row 1
Pop 1
Row*Pop 1

October Density

Effect Num DF
Blk 3
Row 1
Pop 2
Row*Pop 2

Table 5. 2002 eastern black nightshade dry weight per plant in Microplots as affected by

soybean row spacings of 19- and 76-cm.

July at East Lansing
Effect Num DF
Blk 3
Row 1
Pop 2
Row*Pop 2
August at East Lansing
Effect Num DF
Blk 3

Den DF

Den DF

3

3

12

12

Den DF

3

3

12

12

Den DF

3

87

F Value

0.12

5.57

1.17

1.17

F Value

0.42

1.88

0.53

2.03

F Value

0.29

7.43

0.28

2.64

F Value

0.69

P Value

0.9419

0.0994

0.3202

0.3202

P Value

0.7520

0.2636

0.6013

0.1739

P Value

0.8332

0.0722

0.7574

0.1123

P Value

0.6155

Row
Pop
Row*Pop
October at East Lansing
Effect
Blk
Row
Pop
Row*Pop
July at Clarksville
Effect
Blk
Row
Pop
Row*Pop
August at Clarksville
Effect
Blk
Row
Pop

Row*Pop

2

Num DF

3

Num DF

Num DF

12

12

Den DF

12

12

Den DF

12

12

Den DF

12

12

88

5.88

0.33

0.03

F Value

0.94

5.37

1.53

1.97

F Value

0.74

10.11

1.69

0.15

F Value

1.06

14.91

0.17

0.14

0.0938

0.7220

0.9742

P Value

0.5201

0.1033

0.2552

0.1823

P Value

0.5952

0.0501

0.2254

0.8656

P Value

0.4821

0.0307

0.8452

0.8726

October at Clarksville
Effect
Blk
Row
Pop

Row*Pop

Table 6. 2002 eastern black nightshade berry dry weight in Microplots as affected by

soybean row spacings of 19- and 76-cm.

East Lansing in August
Effect
Blk
Row
Pop
Row*Pop
East Lansing in October
Effect
Blk
Row
Pop
Row*Pop
Clarksville in August
Effect

Blk

Num DF

2

Num DF

3

Num DF

3

Num DF

3

Den DF

3

3

12

12

Den DF

3

3

12

12

Den DF

12

12

Den DF

3

89

F Value

1.83

24.44

0.39

0.94

F Value

1.00

2.05

0.37

0.37

F Value

0.99

1.93

0.89

0.88

F Value

1.00

P Value

0.3157

0.0159

0.6884

0.4171

P Value

0.5000

0.2472

0.6967

0.6967

P Value

0.5023

0.2593

0.4343

0.4381

P Value

0.4989

Row 1 3 1.81 0.2711

Pop 2 12 0.92 0.4245

Row*Pop 2 12 0.90 0.4311

Clarksville in October

Effect Num DF Den DF F Value P Value

Blk 3 3 0.85 0.5508

Row 1 3 14.91 0.0307

Pop 2 12 1.58 0.2453

Row*Pop 2 12 1.56 0.2499

Table 7a. Effect of soybean row spacing, plant population, and eastern black nightshade

on microplot soybean yield at East Lansing in 2002.

Effect Num DF Den DF F Value P Value
Row 1 3 1.06 0.3791
Pop 2 12 0.37 0.6955
Row*Pop 2 12 1.56 0.2509
Herb 1 18 0.33 0.5738
Row*Herb l 18 0.68 0.4190
Pop*Herb 2 18 1.39 0.2745
Row*Pop*Herb 2 18 0.61 0.5545

Table 7b. Effect of soybean row spacing, plant population, and eastern black nightshade
on microplot soybean yield at Clarksville in 2002.
Effect Num DF Den DF

F Value P Value

Row 1 3 0.00 0.9534

90

Pop 2 12 0.22 0.8011

Row*Pop 2 12 1.08 0.3532
Herb 1 18 1.05 0.3139
Row*Herb 1 18 0.00 0.9610
Pop*Herb 2 18 1.14 0.3335
Row*Pop*Herb 2 18 3 .02 0.0639

Table 8. Effect of soybean row spacing, population, and herbicide treatment on soybean

yields at East Lansing in 2001.

Effect Num DF Den DF F Value P Value
Row 1 3 0.67 0.4738
Pop 1 6 27.30 0.0020
Row*Pop 1 6 0.00 0.9820
Herb 3 36 2.60 0.0674
Row*Herb 3 36 4.58 0.0081
Pop*Herb 3 36 0.28 0.8360
Row*Pop*Herb 3 36 1.76 0.1730

Table 9a. Effect of soybean row spacing, population, and herbicide treatment on soybean

main plot yield at East Lansing in 2002.

Effect Num DF Den DF F Value P Value
Rep 3 3 4.26 0.1325
Row 1 3 0.05 0.8369
Pop 2 12 2.45 0.1281

Row*Pop 2 12 2.17 0.1570

91

Herb 3 54 2.26 0.0920

Row*Herb 3 54 1.36 0.2658
Pop*Herb 6 54 0.51 0.7963
Row*Pop*Herb 6 54 1.94 0.0907

Table 9b. Effect of soybean row spacing, population, and herbicide treatment on soybean

main plot yield at Clarksville in 2002.

Effect Num DF Den DF F Value P Value
Rep 3 3 10.60 0.0005
Row 1 3 30.79 <0.0001
Pop 2 12 11.97 0.0008
Row*Pop 2 12 0.36 0.7031
Herb 3 54 8.18 0.0001
Row*Herb 3 54 0.53 0.6652
Pop*Herb 6 54 6.04 <0.0001
Row*Pop*Herb 6 54 1.61 0.1617

92

CHAPTER 3 ANOVA TABLES

Table 1. Effect of neutral density Shading on the cumulative emergence of eastern black

nightshade and hairy nightshade.

Source
Rep
Species
Shade

Species*Shade

DF

4

1

3

3

F Value

0.15

13.74

3.70

0.79

P Value

0.9608

0.0004

0.0159

0.5041

Table 2. Effects of neutral shading on reproductive, leaf, total dry weights, leaf area, and

specific leaf area of eastern black nightshade and hairy nightshade.

Reproductive Dry Weight

Source
Rep
Species
Shade
Species*Shade
Leaf Dry Weight
Source
Rep
Species
Shade

Species*Shade

DF

DF

F Value

0.33

2.40

28.92

0.42

F Value

0.12

7.08

47.85

0.12

93

P Value

0.8060

0.1251

<0.0001

0.7381

P Value

0.9487

0.0093

<0.0001

0.9477

Total Dry Weight
Source
Rep
Species
Shade
Species*Shade
Leaf Area
Source
Rep
Species
Shade
Species*Shade
Specific Leaf Area
Source
Rep
Species
Shade

Species*Shade

DF

DF

DF

P Value

0.14

1.82

43.19

0.09

F Value

0.16

14.30

6.56

0.89

F Value

1.48

1.09

29.52

0.66

94

P Value

0.9329

0.1809

<0.0001

0.9628

P Value

0.9256

0.0003

0.0005

0.4481

P Value

0.2268

0.2992

<0.0001

0.5764

Table 3. Comparison of radiation quality on the reproductive, leaf, total dry weights, leaf

area, and specific leaf area of eastern black nightshade and hairy nightshade.

Reproductive Dry Weight
Source DF F Value P Value
Rep 3 0.33 0.8060
Species 1 2.40 0.1251
Shade 3 28.92 <0.0001
Species*Shade 3 0.42 0.7381
Leaf Dry Weight
Source DF F Value P Value
Rep 3 0.12 0.9487
Species 1 7.08 0.0093
Shade 3 47 .85 <0.0001
Species*Shade 3 0.12 0.9477
Total Dry Weight
Source DF F Value P Value
Rep 4 0.15 0.9329
Species 1 13 .74 0.1809
Shade 3 3.70 <0.0001
Species*Shade 3 0.79 0.9628

95

Leaf Area
Source
Rep
Species
Shade
Species*Shade
Specific Leaf Area
Source
Rep
Species
Shade

Species*Shade

DF

DF

F Value

0.16

14.30

6.56

0.89

F Value

0.34

4.62

9.93

1.14

96

P Value

0.9256

0.0003

0.0005

0.4481

P Value

0.7941

0.0382

0.0004

0.3304

    

      

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