Corn Gluten Meal as an Alternative Weed Control Option for Spring-Transplanted Onions

Abstract

Successful screening of suitable onion (Allium cepa L.) varieties, viable production areas, and potential marketing options suggest that onions are a potential alternative crop for Oklahoma and northeast Texas. Unfortunately, onion's slow growth rate, short height, non-branching plant structure, low leaf area, and shallow root system can result in a total loss of marketable yields as a result of weed competition. Field research was conducted in 2002 and 2003 in southeast Oklahoma (Lane, OK) to determine the weed control efficacy of selected preemergent synthetic herbicides and corn gluten meal (CGM) for use in spring-transplanted onion cv. Hybrid Yellow Granex PRR, production. There were 21 treatments [12 synthetic herbicide treatments, 5 CGM application rates, a full-season weed-free (hand-weeded) treatment, a full-season weedy-check, a partial-season weed-free (weed-free for the first half of the growing season), and a weedy-check without onions]. Weed cover and weed control ratings were collected at 46 days after planting (DAP) and at harvest. The synthetic herbicide treatments resulted in significantly greater weed control at 46 DAP and harvest compared to all CGM application rates. The highest CGM rate (4,000 kg·ha) did maintain fair, 72.1%, total weed control and good, 82.7%, broadleaf weed control until 46 DAP. Among the synthetic herbicides, pendimethalin provided the best early and full season weed control.

Full text

Corn Gluten Meal
as an Alternative Weed Control Option
for Spring-Transplanted Onions
Charles L. Webber III
James W. Shrefler
Merritt J. Taylor
ABSTRACT. Successful screening of suitable onion
(Allium cepa
L.)
varieties, viable production areas, and potential marketing options sug-
gest that onions are a potential alternative crop for Oklahoma and north-
east Texas. Unfortunately, onion's slow growth rate, short height,
non-branching plant structure, low leaf area, and shallow root system
can result in a total loss of marketable yields as a result of weed competi-
tion. Field research was conducted in 2002 and 2003 in southeast
Oklahoma (Lane, OK) to determine the weed control efficacy of Se-
Charles L. Webber III (E-mail; cwebber-usda@lane-ag.org
) is affiliated with the
United States Department of Agriculture, Agricultural Research Service, South Cen-
tral Agricultural Research Laboratory, P.O. Box 159, Lane, OK 74555.
James W. Shrefler (E-mail: jshreflerokstate@lane-ag.Org)
is affiliated with the
Department of Horticulture and Landscape Architecture and Merritt J. Taylor (E-mail:
mtaylor-okstate@
lane- ag.org
) is affiliated with Department of Agricultural Econom-
ics, Oklahoma State University, P.O. Box 128, Lane, OK
74555.
Address correspondence to: Charles L. Webber HI at the above address.
The authors thank Buddy L. Faulkenberry HI for maintaining the field experiments
and data collection. Mention of a trademark, vendor, or proprietary product does not
constitute a guarantee or warranty of the product by the USDA and does not imply its
appro'al to the exclusion of other products that may also be suitable.
The article was prepared by a USDA employee as part of his official duties. Copy-
right protection under US copyright law is not available for such works, and there is no
copyright to transfer. The fact that the private publication in which the article appears is
itself copyrighted does not affect the material that is a work product of the US Govern-
ment, which can be freely reproduced by the public.
International Journal of Vegetable Science, Vol. 13(3) 2007
Available online at http://ijvs.haworthpress.com
© 2007 by The Haworth Press. All rights reserved.
doi:10.l300/J5l2vl3fl03_03

17

18

INTERNATIONAL JOURNAL OF VEGETABLE SCIENCE
lected preemergent synthetic herbicides and corn gluten meal (CGM) for
use in spring-transplanted onion cv. Hybrid Yellow Granex PRR, pro-
duction. There were 21 treatments 112 synthetic herbicide treatments,
5
CGM application rates, a full-season weed-free (hand-weeded) treat-
ment, a full-season weedy-check, a partial-season weed-free (weed-free
for the first half of the growing season), and a weedy-check without on-
ions]. Weed cover and weed control ratings were collected at 46 days af
-
ter planting (DAP) and at harvest; The synthetic herbicide treatments
resulted in significantly greater weed control at 46 DAP and harvest
compared to all CGM application rates. The highest CGM rate (4,000
kg-ha
-1
) did maintain fair, 72.1%, total weed control and good,
82.7%, broadleaf weed control until 46 DAP. Among the synthetic her-
bicides, pendimethalin provided the best early and full season weed
control.
doi:lO.1300/J512v13n03
03
[Article copies available for afeefroin
The Haworth Document Delivery Service: 1-800-HA WORTH. E-mail address:
<docdeliveiy@haworthpress. coin> %Vebsire: <http://www.Haworth
Press corn>
© 2007
by The Haworth Press. All rights reserved. /
KEYWORDS.
A Ilium cepa,
corn gluten meal, onion, oxyfluorfen,
pendimethalin, weed competition
INTRODUCTION
Oklahoma producers are interested in sweet onion
(A
ilium cepa L.)
as an alternative crop for farm diversification (McCraw, 1990; Shrefler,
2004). Screening for suitable onion cultivars for Oklahoma production
continues for both fall direct-seeded (McCraw, 1990; Shrefler, 2001,
2004) and spring transplanted onions (Shrefler, 2002, 2004). Further re-
search has demonstrated the feasibility of producing onion transplants
for spring production by fall direct-seeding in hoop-houses (Shrefler et
al., 2004). However, the lack of weed control can result in the total loss
of marketable onions (Wicks et al., 1973). Onions do not compete well
with weeds due to their slow growth rate (Wicks et al., 1973; Umeda et
al., 1998; Bell and Boutwell, 2001), short height (Singh et al., 1992),
non-branching plant structure (Singh et al., 1992), low leaf area (Dunan
et al., 1996; Bell and Boutwell, 2001), and shallow root system (Singh
et al., 1992).
Although mechanical weed control through cultivation is useful for
controlling weeds between rows, it is ineffective for controlling weeds
between plants within rows. Chemical weed control is an alternative to

Webber, Shrefler, and Taylor

19
hoeing or hand removal of weeds from within the crop row. Potential
chemical weed control options include conventional synthetic herbi-
cides such as pendimethalin
[N-(
l-ethyl propyl)-3,4-dimethYl-2,6dini
trobenzenamine] and oxyfluorfen [2-chloro- I -(3-ethoxy-4-nitrophen-
oxy)-4-(trifluoromethyl)benZefle], but also include alternative organic
herbicides such as corn gluten meal (CGM). Pendimethalin is a
dinitroaniline herbicide (Ahrens, 1994) used as a preemergence or early
postemergence herbicide registered for use in many crops including
transplanted dry onion bulbs at rates of 0.55-1.66 kg-ha
-
' ai) [Prowl 3.3
EC, American Cyanamid Co., Wayne,
NJ
)],
and
0.56-1.68
kg-ha-
1
ai
(Sharp, 2002) for control of annual grass and broadleaf weeds (Ahrens,
1994). Oxyfluorfen is a diphenyleth
,
er herbicide used as a preemergence
or over-the-top postemergence herbicide for control of small-seeded
broadleaf weeds and suppression of annual grass weeds in many crops
(Ahrens, 1994), including transplanted onions (0.56 kg aiha' maxi-
mum per season) [Goal 2XL, Dow AgroSciences LLC, Indianapolis,
IN)] and 0.13 - 0.28 kg-ha-
1
ai (Sharp, 2002). Research by Westra et al.
\(1990) using 0.34 kg-ha
-1
ai oxyfluorfen and Singh etal. (1992) using
\pendimethalin at 1.0 and 1.5 kg-ha-
1
ai, oxyfluorfen at 0.10 and 0.15
kg-ha-
1
ai, and tank mixes of pendimethalin with either 0.75 or 1.0
kgha' ai with oxyfuorfen 0.1 kg-ha-
1
ai did not result in injury to on-
ion transplants.
When a crop such as onion lacks a competitive advantage, it often re-
quires an increase in the amount, duration, and diversity of herbicides
needed to control the weeds, resulting in a greater environmental con-
cern (Dunan et al., 1996). Weed control systems usually benefit from
inclusion of alternative weed control methods rather than sole reliance
on conventional synthetic herbicides. Alternative weed control methods
include crop rotations, cover crops, planting systems, mechanical meth-
ods, and organic herbicides. In addition, a combination of several weed
species usually infest a given production area or field. It is also impor-
tant to develop integrated weed control systems to address a wide range
of weed control and production scenarios.
CGM is a certified organic material for organic crop production.
Christians (1993) was the first to determine that soil-incorporated corn
meal was phytotoxic, reducing creeping bentgrass
(Agrostis palustris
Huds.) establishment. It was also determined that it was the CGM frac-
tion that produced the greatest inhibitory effect and reduced root forma-
tion in several weed species, including creeping bentgrass
(Agrostis
palustris Huds.) and crabgrass
(Digitaria
spp.). CGM is the by-product
of the wet-milling process of corn (Quarles, 1999; Bingaman and Chris-

20

INTERNATIONAL JOURNAL OF VEGETABLE SCIENCE
tians, 1995). The powder (McDade, 1999) has been used as a compo-
nent in dog, fish, and livestock feed (Quarles, 1999; Christians 1991,
1995).
In greenhouse studies, Bingaman and Christians (1995) determined
that CGM applied at 3,240 kg-ha-
1
reduced plant survival, shoot length,
and root development for 22 weed species tested, whether the CGM was
applied to the soil surface as a preemergence herbicide or mixed into the
top 2.54 cm as a preplant-incorporated herbicide. Although plant devel-
opment was reduced for all weeds tested, the extent of susceptibility dif-
fered across species. Plant survival and root development was reduced
by at least 70% and shoot length by at least
50%
for black nightshade
(Solanurn nigrurn L.),
common lambsquarters
(Chenopendium album
L.),
creeping bentgrass, curly dock
(Rumex crispus L.),
purslane
(Por-
tulaca oleracea L.),
and redroot pigweed
(Amaranthus retroflexus L.).
When CGM was applied as a preplant incorporated herbicide, the fol-
lowing weeds had at least a
50%
reduction in plant survival and shoot
length and at least an 80% reduction in root development: catchweed
bedstraw
(Galium aparine L.),
dandelion
(Taraxacum officinale
Weber),
giant foxtail
(Setariafaberi
Herrm.), and smooth crabgrass
[Digitaria
ischaemum
(Schreb.) Schreb. ex Muhl]. Plant survival was less than
31 %for barnyardgrass
[Echinochloa crus-galli (L.)
Beauv.] and vel-
vetleaf
(Abutilon theophrasti
Medic.). Field research was conducted in
southeast Oklahoma (Lane, OK) to determine the weed control efficacy
of selected preemergent synthetic herbicides and CGM for use in
spring-transplanted onion production.
MATERIALS AND METHODS
There were 21 weed control treatments with 4 replications applied to
spring-transplanted onions in 2002 and 2003. Certified onion seeds
(cv. Hybrid Yellow Granex PRR) were planted into Speedling (r)
(Speedling, Inc., Sun City, FL) trays on II Dec. 2001 and 2002 and
grown in the greenhouse until just prior to transplanting, when they
were hardened off outside and prepared for transplanting to the field.
Prior to transplanting, the Bernow fine-loamy, siliceous, thermic
Glossic Paleudalf soil was plowed to incorporate the winter wheat cover
crop. Fertilizer was applied according to recommendations (Motes and
Roberts, 1994) and incorporated prior to preparing raised beds (1.4 m
wide). The beds were on 1.8 m centers and oriented east to west with a
1.5-m alley between the 3.0-rn long plots.

Webber, Shrefler, and Taylor

21
On 14 March 2002 and 26 March 2003, onion seedlings were trans-
planted in two rows on the raised beds with 91 cm between rows. In 2002,
onion transplants were thinned in all plots to uniform stands of I plant/
15.2 cm within rows (20 plants/3m) with a total of 40 plants per 3-rn plot
(71,758 plantsha'). In 2003, due to transplanting conditions, the onions
were transplanted and thinnedto a uniform I plant/20.3 cm (15 plants/
3m) with a total of 30 plants per 3-rn plot (53,818 plantsha').
Herbicide applications included synthetic [Prowl 3.3 EC (pendi-
methalin), American Cyanamid Company, and Goal 2XL (oxyfluorfen)
Dow AgroSciences LLC] and organic (CGM) herbicides. Although
there are other preemergence herbicides registered for use for trans-
planted onions, these herbicides provide consistently high weed control
and crop safety in our production area. The 21 weed control treatments
included 12 synthetic herbicide treatments,
5
CGM application rates, a
full-season weed-free (WF) (hand-weeded) treatment, a full-season
weedy-check, a partial-season weed-free (weed-free for the first half of
the growing season, 46 days after planting (DAP)), and a weedy-check
\without onions. A weedy-check without onions was included to isolate
the competitive impacts of the onions and the weed control treatments.
Within 24 hrs of transplanting, the synthetic herbicides (pendimethalin
and oxyfluorfen) were applied at 187 Lha', 276 kPa, with a CO2
backpack sprayer equipped with XR8002VS (Spraying Systems Co.,
Wheaton, IL) nozzles on 51-cm spacing. Synthetic herbicides were ap-
plied at three rates. The herbicide treatments included pendimethalin
applications at 0.5 kg-ha-
1
ai (ai = active ingredients of the herbicide
applied), 1.0 kg-ha
-
' ai and 1.5 kg-ha
-
ai, oxyfluorfen at 0. 1, 0.2, and
0.3 kg-ha-
1
ai, and tank-mixed at these three levels. In addition, the
highest rate of each herbicide treatment, pendirnethalin at
1.5
kg -ha-
ai, oxyfluotfen at 0.3 kg-ha-
1
ai, and the tank mix of pendimethalin at
1.5
kg-ha-
1
ai with oxyfluorfen at 0.3 kgha' ai were applied and kept
weed-free by hand-weeding.
CGM was applied by hand to the soil surface and not- incorporated,
spreading the dry powdered material (Alliance Milling Company,
Denton, Texas) at 4 rates (1,000, 2,000, 3,000, and 4,000 kg-ha-
1
) to
determine weed control efficacy. A weed-free (hand-weeded) treatment
was also combined with the highest CGM rate (4,000 kg-ha
-1
). The
other weed control treatments included a full-season weedy-check
(weeds allowed to grow), a full-season WF hand-weeded treatment, a
partial-season weed-free (weed-free for the first half of the season), and
an onion-free weedy-check (no onions and no weed control). The on-

22

INTERNATIONAL JOURNAL OF VEGETABLE SCIENCE
ion-free treatment was included to determine the effect of onion
competition on weed growth.
Weed cover and weed control ratings were made at midseason 46
DAP and at harvest for total, broadleaf, and grass weeds. The weed
cover ratings represent the percentage weed cover within a treatment
plot area that is covered by weeds where 0 is no weed cover and 100 is
100% of the plot area is covered by weeds. The weed control ratings
represent the percentage weed control for an experimental treatment
compared to the weedy-check with 0 for no weed control and 100 for
complete control. Weed cover and weed control ratings were used
rather than weed counts and biomass collections as a result of the large
number of plots, 84 plots per year, and the destructive nature of the bio-
mass samples. The onions were harvested on 17 June 2002
(95
DAP)
and 17 June 2003 (83 DAP). Onion yields resulting from the weed con-
trol treatments will be discussed in detail in a manuscript devoted to that
subject.
Rainfall during the growing season, from transplanting to harvest, for
2002 was
53.8
cm (16.3 cm during the first week alone) compared to
19.8 cmfor 2003. In 2003, an additional 6.4 cm of supplemental water
was added through sprinkler irrigation to provide a seasonal total of
26.2 cm. The 30 year average rainfall for the location from 15 March to
15 June is 36.0 cm.
The experiment was RCBD with four replications and conducted in
2002 and 2003. All data were subjected to ANOVA and mean separa-
tion using LSD with P = 0.05 (SAS Inc., SAS, Cary, NC). The percent-
age weed cover and weed rating data were prepared for analyses using a
square root arcsine transformation to normalize the data. Mean differ-
ences were determined using the transformed data and the non-trans-
formed data values are reported using the mean differences determined
with the transformed data.
RESULTS AND DISCUSSION
Crop injury.
No injury was observed on the onion leaves or the visual
portion of the bulbs as a result of any of the weed control treatments for
either year (data not shown). These results are consistent with research
with onion transplants by Westra et al. (1990) using a higher rate of
oxyfluorfen (0.34 kg-ha' ai) and Singh et al. (1992) using pendi-
methalin at 1.0 and
1.5
kg-ha- ' ai, oxyfluorfen at 0.10 and 0.15 kg-ha-
1

Webber, Shrefler, and Taylor

23
ai, and tank mixes of pendimethalin with either 0.75 or 1.0 kg-ha
-
' ai
with oxyfuorfen 0.1 kg-ha
-
' ai.
Others have reported herbicide injury to onions with applications of
CGM (McDade and Christians, 2000), pendimethalin (Umeda et al,
1998), and oxyfluorfen (Sieczka et al., 1982), although in these cases
phytotoxicity was present on direct-seeded onions rather than trans-
plants. Research has shown that pendimethalin and oxyfluorfen can be
safely applied to direct-seeded onions (Cudney and Orloff, 1988; Umeda
et al., 1998), but greater care is required with the application rates, ap-
plication timing, and the irrigation methods when pendimethalin is used
for direct-seeded onions (Umeda et al.; 1998).
Mid-season weed cover (46 DAP).
There were no significant year-
y-treatment interactions for the weed ratings at 46 DAP (Table 1), and
the weed cover and weed control data for 46 DAP is averaged across
treatments (Table 2) and years (Table 3). There were no significant dif-
ferences between years at 46 DAP for any of the weed cover and weed
control data (Table 2).
Total, broadleaf and grass weed cover remained low, less than 29%,
for all weed control treatments at 46 DAP (Table 3). The weedy-check
treatments, with and without onions, had the highest weed presence for
total, broadleaf, and grass weeds, 28.8%,
22.5,
and 6.3%, respectively
(Table 3). The lack of differences between weeds in onion-free weedy-
check and weedy-check onion treatment is an indication of the low
competitive impact of onions on weeds as reported elsewhere (Wicks et
al., 1973; Singh et al., 1992; Dunan et al., 1996; Umeda et al.
-
,'I 998; Bell
and Boutwell, 2001). At 46 DAP the weedy-check had 78% broadleaf
and 22% grass weeds (Table 3). The primary broadleaf weeds within
the weedy-check included spiny amaranth
(Amaranthus spinosus L.),
50-60%,
and tumble pigweed
(Amaranthus albus L.),
10-20%, cutleaf
groundcherry
(Physalis angulata L.),
15-20%, and less than I % of
Pennsylvania smartweed
(Polygonurn pensylvanicum L.).
The primary
grass weeds in the weedy-checks included a mix of smooth
(Digitaria
ischaemum
(Schreb.) Schreb. ex Muhl.) and hairy crabgrass
(Digitaria
sanguinalis (L.)
Scop.), 75-85%, goosegrass
(Eleusine indica (L.)
Gaertn.), 15-20%, and less that
2.5%
of either Bermudagrass
(Cynodon
dactylon (L.)
Pers.) or barnyardgrass
[Echinochloa crus-galli (L.)
Beauv.].
All treatments receiving any weed control method had significantly
less weed cover than the weedy-check and the onion-free weedy check,
and the two weedy checks were not significantly different (Table 3). All

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26

Webber, Shrefler, and Taylor

27
treatments receiving conventional herbicides resulted in significantly
less weed cover than the four CGM only treatments (Table 3).
Mid-season weed control (46 DAP).
All synthetic herbicide weed
control treatments resulted in fair (70% to 80%) to good (80% to 90%)
total and broadleaf weed control at 46 DAP (Table 3). Grass weed con-
trol was less than 70% for the lowest two rates of oxyfluorfen, com-
pared to over 70% control for any herbicide treatment containing
pendimethalin (Table 3). These results indicate that pendimethalin pro-
vided the best early season weed control.
Even with the very low weed pressure during the first half of the sea-
son, the three lowest CGM rates had very low weed control, less than
50% for total, broadleaf, and grass control (Table 3). The highest CGM
rate (4,000 kg-ha-
1
) maintained fair, 72.1%, total weed control and
good (82.7%), broadleaf weed control until 46 DAP. Although CGM
did provide initial weed control for onion, and more so for broadleaf
than grass weeds, additional weed control may be required.
Harvest weed cover.
At harvest there was a significant year
X
treat-
ment interaction for the broadleaf and grass weed cover and weed con-
trol data (Table 1); so these results will be discussed by year (Tables 4
and
5).
There was a 100% weed cover in the weedy-check treatments at har-
vest (Table 6). CGM treatments exhibited less than 1% total weed con-
trol at harvest, essentially no different from the weedy-checks. Even the
partial-season (weed free until 46 DAP) treatment had 99.3% weed
cover and less than 1% control at harvest (Table 6). This result indicates
the intense weed establishment and aggressive weed growth through the
crop cycle, even when onions are kept weed-free for the first 46 DAP.
The best residual weed control, although still very low, was in treat-
ments containing pendimethalin at 1.0 or 1
.5
kg-ha- ' ai, with'a slight in-
crease in weed control when tank-mixed with oxyfluorfen (Table 6).
Although the relative weed control advantages and disadvantages
continue across (Table 6) and within years (Tables 4 and 5) for total
weed control at harvest, the weed pressure differences for broadleaf and
grass weeds between years were involved in the significant year-
by-treatment interaction (Tables 4 and
5).
When comparing weed cover
at harvest between years, there is a general reversal between which
weed type, broadleaf or grass weeds, was predominant (Tables 4, 5)
even though there were no significant differences in weed cover at 46
DAP (Table 2). In both, years there was 100% weed cover in the
weedy-check at harvest, the distribution between broadleaf and grass
weeds was different between years (Tables 4, 5). In 2002, the broadleaf

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Webber, Shrefler, and Taylor

31
weed cover,
62.5%,
and grass weed cover, 37.5%, were reversed com-
pared to broadleaf and grass weed cover in 2003, 17.5% and 82.5%, re-
spectively. Not only were there no significant differences in weed cover
between years at 46 DAP for the weedy-check; but the weed cover de-
velopment from 46 DAP to harvest, as seen in the partial-season
weed-free treatment, was similar when comparing years for the broad-
leaf (29.8% vs. 28.3%) and grass cover (68.8% vs. 71.8%), 2002 and
2003, respectively (Tables 4, 5).
The primary environmental difference between years was higher pre-
cipitation in 2002, and the later planting date in 2003. It is unlikely that
delaying planting by 12 days in 2003 would result in such a reversal in
weed composition between years, especially when the differences were
not measurable at 46 DAP. It is more likely that differences in soil mois-
ture due to rainfall and irrigation between years, 2002
(53.8
cm rainfall)
and 2003 (19.8 cm rainfall or 26.2 cm with irrigation added) were re-
sponsible for seasonal differences in weed growth.
Even with the very low weed pressure during the first half of the sea-
son, the three lowest CGM rates had very low weed control-less than
50%
for total, broadleaf, and grass control. The highest CGM rate
(4,000 kg-ha- ) did maintain fair, 72.1%, total weed control and good,
82.7%, broadleaf weed control until 46 DAP. The synthetic herbicide
treatments resulted in significantly better weed control than the highest
and best CGM rate. When comparing the synthetic herbicides, pendi-
methalin provided the best early-season weed control.
The early effects of CGM were short-lived and essentially no differ-
ent from the weedy-check at harvest. The CGM material was no longer
visual on the soil surface at 46 DAP. The best residual weed control, al-
though still very low, was in treatments containing pendimethalin at 1.0
and 1.5 kg-ha-
1
ai, with a slight increase in weed control when tank-
mixed with oxyfluorfen. These results illustrate the importance of sea-
son-long weed control and the importance of additional mid-season
measures to provide season-long weed control. The post emergence
application of a synthetic graminicide such as sethoxydim (
2
-[
l
-
1-one) and fluazifop ((R)-2- { 4[5(trifluoromethyl)-2-pyridylOXy]phen-
oxy}propionic acid) would certainly provide significantly greater grass
control. In an organic production system, the post-directed of applica-
tion of organically certified contact herbicides have the potential to en-
hance the season long weed control in transplanted onions.

32

INTERNATIQURNAL OF VEGETABLE SCIENCE
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
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doi: 10.1 3005512v I 3n03_03
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