Glyphosate-resistant Volunteer Research Articles

Control of Volunteer Glyphosate-Resistant Corn in Soybean With Clethodim Plus Adjuvants

In Ontario, volunteer glyphosate-resistant (GR) corn is one the most common annual grass escapes in GR soybean sprayed with glyphosate. Six field experiments were established in southwestern Ontario during 2021 and 2022 to determine volunteer GR corn control in soybean with glyphosate (900 g ae ha-1) + clethodim (45 g ai ha-1) plus three adjuvants. At 1, 2, and 4 WAA, there was no visible soybean injury from the herbicide treatments evaluated. At 1 WAA, glyphosate + clethodim controlled volunteer GR corn 23%; the addition of the adjuvants Amigo®, Journey HSOC®, and StrikeLock® at 0.5% v/v improved control to 45 to 49%; there was no statistical difference in volunteer corn control among the adjuvants evaluated. At 2 WAA, glyphosate + clethodim controlled volunteer GR corn 23%; the addition of the adjuvants Amigo®, Journey HSOC®, and StrikeLock® at 0.5% v/v improved the control to 73 to 79%; there was no statistical difference in volunteer corn control among the adjuvants evaluated.  At 4 WAA, glyphosate + clethodim controlled volunteer GR corn 16%; the addition of the adjuvants Amigo®, Journey HSOC®, and StrikeLock® at 0.5% v/v improved the control to 91 to 95%; there was no statistical difference in volunteer corn control among the adjuvants evaluated. Volunteer corn interference reduced soybean yield by up to 23% in this trial (highest yielding treatment compared to the non-treated control). Reduced volunteer corn interference with clethodim increased soybean yield 13%. Reduced volunteer corn interference with clethodim plus an adjuvant increased soybean yield 27 to 31%. This study concludes that the addition of Amigo®, Journey HSOC®, or StrikeLock® to clethodim improves volunteer GR corn control resulting in a concomitant increase in soybean yield.

Economic impact of glyphosate-resistant weeds on major field crops grown in Ontario

AbstractLimited information exists on the global economic impact of glyphosate-resistant (GR) weeds. The objective of this manuscript was to estimate the potential yield and economic loss from uncontrolled GR weeds in the major field crops grown in Ontario, Canada. The impact of GR weed interference on field crop yield was determined using an extensive database of field trials completed on commercial farms in southwestern Ontario between 2010 and 2021. Crop yield loss was estimated by expert opinion (weed scientists and Ontario government crop specialists) when research data were unavailable. This manuscript assumes that crop producers adjust their weed management programs to control GR weeds, which increases weed management costs but reduces crop yield loss from GR weed interference by 95%. GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed would cause an annual monetary loss of (in millions of Can$) $172, $104, $11, $3, and $0.3, respectively, for a total annual loss of $290 million if Ontario farmers did not adjust their weed management programs to control GR biotypes. The increased herbicide cost to control GR volunteer corn, horseweed, waterhemp, giant ragweed, and common ragweed in the major field crops in Ontario is estimated to be (in millions of Can$) $17, $9, $2, $0.1, and $0.02, respectively, for a total increase in herbicide expenditures of $28 million annually. Reduced GR weed interference with the adjusted weed management programs would reduce farm-gate monetary crop loss by 95% from $290 million to $15 million. This study estimates that GR weeds would reduce the farm-gate value of the major field crops produced in Ontario by Can$290 million annually if Ontario farmers did not adjust their weed management programs, but with increased herbicide costs of Can$28 million and reduced crop yield loss of 95% the actual annual monetary loss in Ontario is estimated to be Can$43 million annually.

Elk (Cervus elaphus) grazing reduces volunteer soybean density

Management of glyphosate resistant volunteer soybean can be challenging and costly in other glyphosate resistant crops. This study examined the effect of elk (Cervus elaphus) grazing on volunteer soybean (Glycine max) management. Volunteer soybean density was assessed in four fields grazed by elk and three without elk in western Manitoba, Canada. This study determined that elk grazing of soybean stubble significantly reduced soybean volunteer density in the following crop. These results demonstrate that winter elk grazing can be an effective management technique for volunteer soybeans.

Influence of 2,4-D, dicamba, and glyphosate on clethodim efficacy of volunteer glyphosate-resistant corn

AbstractManagement of volunteer glyphosate-resistant (GR) corn may be problematic in soybean resistant to glyphosate and 2,4-D or dicamba, as auxinic herbicides often antagonize graminicide efficacy. Field and greenhouse trials were conducted using mixtures of 2,4-D or dicamba in combination with glyphosate and clethodim-A (formulated without an adjuvant) or clethodim-SM (adjuvant-inclusive formulation) to determine the effect on volunteer GR corn control. Neither auxinic herbicide reduced clethodim efficacy, regardless of clethodim rate or formulation in field trials. However, the addition of glyphosate to these mixtures at the 35 g ai ha−1 clethodim dose reduced control from clethodim-A and clethodim-SM by 62% to 75% and 27% to 47%, respectively. Increasing the clethodim dose to 105 g ha−1 or greater in combination with glyphosate and either auxinic herbicide generally restored clethodim efficacy (74% to 98% control); in one site-year, the addition of glyphosate plus dicamba to clethodim-A at 140 g ha−1 still reduced control by 34%. In greenhouse experiments, clethodim-A efficacy was reduced by 17% and 28% when applied with glyphosate plus 420 and 1,680 g ae ha−1 2,4-D, respectively, in the absence of crop oil concentrate (COC). Increasing the dose of dicamba in a similar mixture had a negligible effect. Irrespective of auxinic herbicide dose, the inclusion of COC to clethodim-A mixtures with glyphosate plus 2,4-D or dicamba resulted in ≥ 90% control. These results specify an enhanced risk of reduced clethodim efficacy on volunteer GR corn when glyphosate is added to mixtures containing 2,4-D or dicamba. To optimize control from these mixtures, clethodim should be applied at ≥ 105 g ha−1 and should include an activator adjuvant in the form of COC and/or an adjuvant-inclusive clethodim formulation. This recommendation contrasts with several labels of clethodim that do not require COC when applied with adjuvant-loaded glyphosate products.

Minimizing competition between glyphosate-resistant volunteer canola (Brassica napus) and glyphosate-resistant soybean: impact of soybean planting date and rate

AbstractIn recent years, soybean acreage has increased significantly in western Canada. One of the challenges associated with growing soybean in western Canada is the control of volunteer glyphosate-resistant (GR) canola, because most soybean cultivars are also glyphosate resistant. The objective of this research was to determine the impact of soybean seeding rate and planting date on competition with volunteer canola. We also attempted to determine how high seeding rate could be raised while still being economically feasible for producers. Soybean was seeded at five different seeding rates (targeted 10, 20, 40, 80, and 160 plants m−2) and three planting dates (targeted mid-May, late May, and early June) at four sites across western Canada in 2014 and 2015. Soybean yield consistently increased with higher seeding rates, whereas volunteer canola biomass decreased. Planting date generally produced variable results across site-years. An economic analysis determined that the optimal rate was 40 to 60 plants m−2, depending on market price, and the optimal planting date range was from May 20 to June 1.

CONTROL OF GLYPHOSATE-RESISTANT VOLUNTEER MAIZE USING ACCase INHIBITING HERBICIDES

ABSTRACT Controlling volunteer plants was aggravated due to the emergence of genetically modified glyphosate-resistant cultivars, requiring new technical recommendations. This work was developed with the objective of evaluating alternatives for chemical control of glyphosate-resistant maize infesting soybean crops, using ACCase inhibiting herbicides. Two experiments were carried out, one in Santa Cruz das Palmeiras (SP) and other in Não-Me-Toque (RS), Brazil. Volunteer maize plants were simulated with seeds of the DKB 390 YGRR2 hybrids, distributed between rows of soybean crops, at the density of 6 plants m-2. Combinations of the herbicides clethodim (65 and 84 g ha-1), sethoxydim (138 and 165 g ha-1), and haloxyfop (36 and 45 g ha-1) were applied at two phenological stages of the soybean crop [three (3T) and six (6T) trifoliate leaves], corresponding to the V4/V5 and V7/V8 stages of the volunteer maize, respectively, resulting in 14 treatments. A treatment without herbicide application and a treatment with manual weeding were included as check plots. Applying graminicides on maize plants at V4/V5 stage resulted in more consistent results and general efficacy. Soybean yield was lower when applying herbicide only on maize plants at V7/V8, in both locations. Therefore, management practices for glyphosate-resistant volunteer maize should be adopted early, on maize plants at the V4/V5 stage, mainly when the maize plants are from lost grains in the harvesting process. The use of the herbicides clethodim and haloxyfop results in consistent control efficacy of volunteer maize plants.

The Effect of Duration of Corn (Zea mays) Interference on Cotton (Gossypium hirsutum) Growth and Yield

Widespread use of glyphosate-resistant (GR) corn in rotation with cotton increases the incidence of volunteer GR corn in subsequent cotton stands. Experiments were conducted in Mississippi in 2011 and 2012 to determine cotton response to volunteer corn present at 0.3, 1.6, or 3.2 plants per m of crop row allowed to persist for zero, one, two, six, eight, 10 and 12 weeks after emergence or until cotton harvest. Cotton maturity was accelerated at a density of 3.2 plants per m of crop row. Neither cotton height nor yield was affected by corn removal timing at the low corn density. Cotton height and yield decreased as the time of corn removal was delayed at the medium and high corn densities. No differences in cotton height were observed from increasing corn density at removal timings up to two weeks after cotton emergence (WACE). At each corn removal timing four WACE and beyond, increasing corn density led to reductions in cotton height. No differences in cotton yield were observed from increasing density at corn removal timings zero or one WACE; increases in corn density at removal timings beyond one WACE generally led to reductions in cotton yield. These data indicate medium to high populations of volunteer corn generally should be removed by four to six WACE to prevent height reductions and yield loss.

The Addition of Dicamba to POST Applications of Quizalofop-p-ethyl or Clethodim Antagonizes Volunteer Glyphosate-Resistant Corn Control in Dicamba-Resistant Soybean

Two studies consisting of six field experiments each were conducted at three locations in southwestern Ontario, Canada, in 2014 and 2015 to evaluate the possible antagonism when dicamba was added to quizalofop-p-ethyl or clethodim for the control of volunteer glyphosate-resistant (GR) corn. At 4 wk after application (WAA), quizalofop-p-ethyl at 24, 30, or 36 g ai ha−1provided 88, 94, and 95% control of volunteer GR corn, respectively. The addition of dicamba at 300 or 600 g ae ha−1to quizalofop-p-ethyl (24 g ha−1) reduced the activity of quizalofop-p-ethyl on volunteer GR corn by 12 and 20%. At 4 WAA, clethodim at 30, 37.5, and 45 g ai ha−1provided 85, 91, and 95% control of volunteer GR corn, respectively. The addition of dicamba at 300 or 600 g ha−1to clethodim (30 g ha−1) resulted in antagonism, causing a reduction in volunteer GR corn by 12 and 11%, respectively. In general, there was greater antagonism when the high rate of dicamba was tank-mixed with the lower rate of the graminicide. There was no antagonistic effect on soybean yield by tank-mixing dicamba with either graminicide at all rates evaluated. Based on these results, volunteer GR corn can be controlled effectively by increasing the rate of the graminicide when tankmixed with dicamba.

Impact of glyphosate-resistant volunteer corn (Zea mays L.) density, control timing, and late-season emergence on yield of glyphosate-resistant soybean (Glycine max L.)

Glyphosate-resistant (GR) volunteer corn is a troublesome weed in soybean fields in a corn-soybean rotation as well as in corn fields in a continuous corn production system. The objectives of this study were to evaluate the impact of (1) different densities of GR volunteer corn on soybean yields, present as individual plants or clumps, controlled at fourth trifoliate (V4), sixth trifoliate (V6), or full flowering (R2) soybean growth stages, and (2) late-season volunteer corn emergence on soybean yields, after being controlled at different soybean growth stages. Field experiments were conducted in 2013 and 2014 under irrigated conditions in Clay County, Nebraska, and under rain-fed conditions in Lancaster County, Nebraska, USA. To maintain the desired number of isolated volunteer corn plants (1250, 2500, 5000, and 10,000 plants ha−1) and clumps (63, 125, 250, and 500 clumps ha−1), individual seeds and/or corn ears were hand-planted in each plot based on their respective target densities. Volunteer corn was controlled with applications of clethodim at V4, V6, or R2 soybean growth stages. Late-season volunteer corn emergence had no effect on soybean yield with volunteer corn densities and control timings at both locations in 2013 and 2014. During the first year of study at Clay County, volunteer corn densities and control timings had no effect on soybean yield. When volunteer corn was left uncontrolled or controlled at the R2 soybean growth stage, yield was the lowest at highest isolated volunteer corn plants (10,000 plants ha−1) plus clump density (500 clumps ha−1) during the second year of study in Clay County (≤5068 kg ha−1) and during both years of study in Lancaster County (≤1968 kg ha−1).

Herbicide Programs for Control of Glyphosate-Resistant Volunteer Corn in Glufosinate-Resistant Soybean

Glyphosate-resistant (GR) volunteer corn is a significant problem weed in soybean grown in rotation with corn in the midwestern United States and eastern Canada. The objective of this study was to evaluate the efficacy of glufosinate applied in single or sequential applications compared with acetyl-coenzyme A carboxylase (ACCase) inhibitors applied alone or tank mixed with glufosinate for controlling GR volunteer corn in glufosinate-resistant soybean. At 15 d after early-POST (DAEP), ACCase inhibitors applied alone controlled volunteer corn 76 to 93% compared to 71 to 82% control when tank mixed with glufosinate. The expected volunteer corn control achieved by tank mixing ACCase inhibitors and glufosinate was greater than the glufosinate alone, indicating that glufosinate antagonized ACCase inhibitors at 15 DAEP, but not at later rating dates. ACCase inhibitors applied alone or tank mixed with glufosinate followed by late-POST glufosinate application controlled volunteer corn and green foxtail ≥ 97% at 30 DAEP. Single early-POST application of glufosinate controlled common waterhemp and volunteer corn 53 to 78%, and green foxtail 72 to 93% at 15 DAEP. Single as well as sequential glufosinate applications controlled green foxtail and volunteer corn greater than or equal to 90%, and common waterhemp greater than 85% at 75 d after late-POST (DALP). Contrast analysis suggested that glufosinate applied sequentially provided greater control of volunteer corn at 15 and 75 DALP compared to a single application. Similar results were reflected in volunteer corn density and biomass at 75 DALP. Volunteer corn interference did not affect soybean yield, partly because of extreme weather conditions (hail and high winds) in both years of this study.

Control of Volunteer Glyphosate-Resistant Canola in Glyphosate-Resistant Sugar Beet

Occurrence of glyphosate-resistant (GR) canola volunteers in GR sugar beet is a management concern for growers in the Northern Great Plains. Field experiments were conducted at the Southern Agricultural Research Center near Huntley, MT, in 2011 and 2012 to evaluate effective herbicide programs to control volunteer GR canola in GR sugar beet. Single POST application of triflusulfuron methyl alone at the two-leaf stage of sugar beet was more effective at 35 compared with 17.5 g ai ha−1. However, rate differences were not evident when triflusulfuron methyl was applied as a sequential POST (two-leaf followed by [fb] six-leaf stage of sugar beet) program (17.5 fb 17.5 or 35 fb 35 g ha−1). Volunteer GR canola plants in the sequential POST triflusulfuron methyl–containing treatments produced little biomass (11 to 15% of nontreated plots) but a significant amount of seeds (160 to 661 seeds m−2). Ethofumesate (4,200 g ai ha−1) PRE followed by sequential POST triflusulfuron methyl (17.5 or 35 g ha−1) provided effective control (94 to 98% at 30 d after treatment [DAT]), biomass reduction (97%), and seed prevention of volunteer GR canola. There was no additional advantage of adding either desmedipham + phenmedipham + ethofumesate premix (44.7 g ha−1) or ethofumesate (140 g ha−1) to the sequential POST triflusulfuron methyl–only treatments. The sequential POST ethofumesate-only (140 fb 140 g ha−1) treatment provided poor volunteer GR canola control at 30 DAT, and the noncontrolled plants produced 6,361 seeds m−2, which was comparable to the nontreated control (7,593 seeds m−2). Sequential POST triflusulfuron methyl–containing treatments reduced GR sugar beet root and sucrose yields to 18 and 20%, respectively. Consistent with GR canola control, sugar beet root and sucrose yields were highest (95 and 91% of hand-weeded plots, respectively) when the sequential POST triflusulfuron methyl–containing treatments were preceded by ethofumesate (4,200 g ha−1) PRE. Growers should utilize these effective herbicide programs to control volunteer GR canola in GR sugar beet. Because of high canola seed production potential, as evident from this research, control efforts should be aimed at preventing seed bank replenishment of the GR canola volunteers.

Competition of Transgenic Volunteer Corn with Soybean and the Effect on Western Corn Rootworm Emergence

Glyphosate-resistant (GR) volunteer corn has emerged as a problematic weed in corn:soybean rotational systems, partly because of the rapid increase in adoption of corn hybrids that contain traits for both glyphosate and insect resistance. Volunteer GR corn can decrease soybean yields. The objectives of this study were to quantify the impact of volunteer corn on soybean growth and yield and determine how volunteer corn densities affect western corn rootworm (WCR) emergence. Volunteer corn seed was hand-planted at targeted densities of 0.5, 2, 4, 8, 12, and 16 seeds m−2at soybean planting and 21 d after planting to evaluate both early- and late-emerging cohorts. WCR emergence was assessed with the use of field emergence traps placed over individual corn plants in the 0.5- and 16-plants-m−2plots in 2008 and 2009. In 2010, WCR emergence traps were also placed over individual and clumped volunteer corn plants at densities of two and eight plants m−2. Soybean yield reductions ranged from 10 to 41% where early-emerging volunteer corn densities ranged from 0.5 to 16 plants m−2. No soybean yield loss occurred with the late-emerging cohort of volunteer corn. Twice as many adult WCRs emerged from a single volunteer corn plant growing at densities of 8 and 16 plants m−2, compared with plots containing 0.5 and 2 plants m−2. These results demonstrate that controlling volunteer corn will not only prevent soybean yield loss, but also may reduce the risk of WCR larval survival after exposure to Bt (Bacillus thuringiensisBerliner derived) corn.

Volunteer Glyphosate-Resistant Corn Interference and Control in Glyphosate-Resistant Sugarbeet

Glyphosate-resistant (GR) sugarbeet is commonly grown in rotation with GR corn, but there is limited information relating to volunteer GR corn interference or control in GR sugarbeet. Field studies were conducted near Lingle, WY and Scottsbluff, NE in 2009 and 2010 to quantify sugarbeet yield loss in response to volunteer corn density and duration of interference, and determine appropriate control practices for use in GR sugarbeet. Hybrid corn resulted in a similar competitive effect on sugarbeet sucrose yield as clumps of F2volunteer corn. Clumps of volunteer corn were controlled 81% compared with 73% for individual plants. Linear regression indicated sucrose yield loss of 19% for each corn plant m−2up to 1.7 plants m−2at three of four experimental sites. Pearson correlation coefficients between percentage sucrose yield loss and proportion of sunlight reaching the top of the sugarbeet canopy ranged from −0.42 to −0.92. The duration of corn interference required to cause a 5% sucrose yield loss (YL5) ranged from 3.5 to 5.9 wk after sugarbeet emergence (WAE) for hand-weeding or herbicide removal, respectively, due to the length of time herbicide-treated volunteer corn continued to shade sugarbeet plants. Differences between herbicide and hand-removal methods were attributed to the time lag between when the treatments were applied and when the corn ceased to block light from the sugarbeet canopy. Sethoxydim generally provided less volunteer corn control compared with either quizalofop or clethodim, and control increased with the addition of an oil adjuvant. If a grower were to implement a volunteer corn control practice 3.5 WAE, economic sugarbeet yield loss would be avoided. In eastern Wyoming and western Nebraska, the sugarbeet crop will typically have between four to eight true leaves at 3.5 WAE, and therefore this would be an optimal time to control volunteer corn. If volunteer corn is being hand weeded, theYL5estimate will also increase, and thus the window of time to control volunteer corn would be wider.

Control of Volunteer Glyphosate-Resistant Soybean in Rice

Two field studies were conducted in 2007 and 2008 to evaluate at-planting burndown and POST herbicide applications targeting volunteer glyphosate-resistant (GR) soybean in rice. In the burndown study, paraquat, glufosinate, and a thifensulfuron plus tribenuron mixture were applied immediately after rice seeding. Paraquat controlled volunteer GR soybean at least 95% at all evaluations both years. Control with glufosinate was greater in 2007 than 2008 due to rainfall that occurred following application the second year. The thifensulfuron plus tribenuron mixture provided similar control in both years, but control never exceeded 71%. Additionally, a study was conducted evaluating POST-applied rice herbicides including propanil (4,480 and 2,240 g ai/ha), triclopyr (420 and 210 g ai/ha), bispyribac-sodium (38 and 19 g ai/ha), penoxsulam (40 and 20 g ai/ha), and halosulfuron (70 and 35 g ai/ha). Control across all POST herbicides and application rates was equivalent (> 95%) 28 and 56 d after application except for propanil, which controlled volunteer GR soybean less than other treatments. Volunteer GR soybean can be effectively managed in a rice production system with at-planting burndown or POST herbicide applications in rice.

Emergence timing of volunteer canola in spring wheat fields in Manitoba

Observational studies of weed emergence provide essential data for the creation and testing of predictive emergence models, with data ideally being collected from a wide range of sites representing a range of environments under which the seedlings of a given species emerge. The spring emergence of genetically engineered glyphosate-resistant volunteer canola was monitored in 20 farmers' commercial wheat fields over 2 yr, 2003 and 2004, in the southwestern region of Manitoba, Canada. Three different tillage systems, low-disturbance direct-seeded, high-disturbance direct-seeded, and conventionally tilled fields, were represented in this sample. Tillage system did not significantly influence the emergence periodicity of volunteer canola, but did influence total densities observed. Total volunteer canola densities in the surveyed fields were variable and ranged from 6 to 2,015 seedlings m−2. Conventionally tilled fields had the lowest densities of volunteer canola seedlings, and high-disturbance direct-seeded fields (no autumn tillage) had the highest densities. Volunteer canola is a relatively early spring emerging plant species requiring minimal accumulated growing degree days for emergence (calculated using a base temperature of 5 C). Emergence curves were steep, with a short window of volunteer canola emergence either prior to or within a spring-seeded wheat crop. To determine what proportion of autumn-broadcast canola seed (simulated harvest losses) would recruit the following spring and the influence of fall or spring tillage on this recruitment, a small plot experiment also was conducted at three sites. The following spring the percentage of canola seedlings that emerged ranged from 1.3 to 9.4% of the seed broadcast, depending upon the tillage treatment. The effect of tillage treatment on canola densities in the small plot experiment was similar to the field survey results.

Control of Volunteer Glyphosate-Resistant Corn (Zea mays) in Glyphosate-Resistant Soybean (Glycine max)

Volunteer corn in soybean can reduce yields, interfere with harvest, and cause unacceptable levels of contamination by its presence in the harvested soybean. In Ontario, soybean frequently follow corn in rotation. The use of glyphosate-resistant corn and soybean varieties has increased dramatically in Ontario. Field studies were conducted at two locations in southwestern Ontario to determine whether quizalofop-p-ethyl, clethodim, and fenoxaprop-p-ethyl can be tank mixed with glyphosate to provide effective control of volunteer glyphosate-resistant corn in glyphosate-resistant soybean. Soybean plots were overseeded with glyphosate-resistant corn and treatments consisting of glyphosate applied alone and tank mixed with full and reduced rates of each graminicide with and without a recommended surfactant. Tank mixing the graminicides and adjuvants with glyphosate did not affect glyphosate weed control or crop tolerance. Use of a recommended adjuvant significantly improved the effectiveness of the graminicides, particularly when reduced rates were applied. Quizalofop-p-ethyl was the most effective graminicide for controlling glyphosate-resistant volunteer corn, followed by clethodim and fenoxaprop-p-ethyl.