Greenhouse and laboratory studies were conducted to determine the degree of dominance of the monogenic sulfonylurea herbicide resistance trait in diploid sugarbeet by comparing the response of homozygous and heterozygous resistant sugarbeet to primisulfuron, thifensulfuron, and chlorimuron on the whole plant and acetolactate synthase (ALS) enzyme level. Progeny tests suggested that the monogenic sulfonylurea herbicide resistance was semidominant. Subsequently, heterozygous resistant (R-1) and homozygous resistant (R-2) sugarbeet lines were sprayed with increasing rates of primisulfuron, thifensulfuron, and chlorimuron, and herbicide rates required for 50% growth reduction (GR50) were determined. GR50 values were also determined for homozygous susceptible sugarbeet lines (S-1 and S-2). The GR50 values indicated that the R-2 sugarbeet was 377, 269, and 144 times more resistant to primisulfuron, thifensulfuron, and chlorimuron, respectively, than susceptible S-2 sugarbeet. In contrast, R-1 sugarbeet was only 107, 76, and 57 times more resistant to primisulfuron, thifensulfuron, and chlorimuron, respectively, than S-1 sugarbeet, indicating at least a twofold difference in the magnitude of resistance between homozygous resistant and heterozygous resistant sugarbeet lines. ALS enzyme activity analysis were consistent with whole plant results. Thus, based on these two, maximum crop resistance can be obtained by developing homozygous resistant cultivars.

Greenhouse and laboratory studies were conducted to determine the effect of 22 postemergence corn broadleaf herbicide combinations on the efficacy of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. Eighteen combinations caused a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, atrazine plus bentazon, bromoxynil, primisulfuron, CGA-152005 plus primisulfuron, MON 12000, and flumetsulam plus clopyralid plus 2,4-D (NAF-73) were evaluated further on the efficacy and foliar absorption of sethoxydim applied to giant foxtail, large crabgrass, and shattercane. In timing studies, applying all herbicide combinations at 7 or 3 d before sethoxydim application eliminated significant antagonistic interactions. However, applying NAF-73, primisulfuron, or CGA-152005 plus primisulfuron 1 d prior resulted in a reduction in sethoxydim efficacy on at least one grass species. Dicamba, atrazine plus dicamba, and atrazine plus bentazon decreased 14C-sethoxydim absorption 9 to 63% across grass species. Replacing crop oil concentrate (COC) with DASH increased sethoxydim absorption when applied with these herbicides but not to the full extent of sethoxydim applied alone with DASH. Sethoxydim efficacy was retained or improved with DASH when applied with dicamba, atrazine plus dicamba, atrazine plus bentazon, or bromoxynil. When primisulfuron, CGA-152005 plus primisulfuron, MON 12000, or NAF-73 was applied with 14C-sethoxydim no effect on sethoxydim absorption was observed. DASH was less effective than COC at restoring sethoxydim efficacy when applied with these herbicides.

Greenhouse and laboratory studies were conducted to determine the effects of tank-mixing the sodium salt of dicamba (Na-dicamba) with imazethapyr on the efficacy and foliar absorption of imazethapyr, applied with non-ionic surfactant (NIS) or methylated seed oil (MSO), by shattercane, giant foxtail, and large crabgrass. The effects of various salt formulations of dicamba and the addition of ammonium sulfate on efficacy, 14C-absorption and on foliar spray retention by the same species were also evaluated. Na-dicamba antagonized imazethapyr efficacy by reducing 14C-absorption. Using MSO instead of NIS prevented antagonism when Na-dicamba was applied at 70 and 140 g/ha and reduced the severity of the antagonism at greater application rates by greatly increasing 14C-absorption compared to NIS. Reductions in 14C-absorption and spray retention were due to the salt formulations of dicamba rather than the parent acid. The addition of ammonium sulfate prevented dicamba antagonism of imazethapyr toxicity to grassy weeds by maintaining 14C foliar absorption and spray retention at normal levels.

Greenhouse and laboratory studies were conducted to determine the effects of bentazon on the crop safety, efficacy, foliar absorption, and translocation of thifensulfuron when it is applied to soybean, velvetleaf, and common lambsquarters. A metabolism study was conducted on soybean. Thifensulfuron applied at 1.1 g ai ha−-1 with 28% urea ammonium nitrate (2.5% v/v) and BAS-0904805 (Dash) adjuvant (0.63% v/v) reduced the growth of velvetleaf and common lambsquarters by an average of 91 and 84%, respectively. The addition of 420 g ai bentazon ha−-1 had no effect on thifensulfuron efficacy in the weed species. Soybean dry weights were decreased by 58% when thifensulfuron was applied at 2.2 g ha−-1 but were decreased by only 36% when bentazon, at 420 g ha−-1, was added. In the absorption study, the addition of bentazon reduced foliar absorption of 14C-thifensulfuron into velvetleaf and common lambsquarters 8 and 24 h after treatment (HAT), but absorption into soybean was not affected. Bentazon reduced the translocation of 14C from thifensulfuron out of the treated leaves of velvetleaf and common lambsquarters by at least 16 and 11%, respectively, beyond 24 HAT. Soybean translocated 18, 29, and 26% of absorbed 14C out of the treated leaflets 24, 72, and 168 HAT, respectively. These translocation values were reduced to 7, 12, and 11%, respectively, when bentazon was tank-mixed with thifensulfuron. Soybean metabolized 35% of recovered 14C-thifensulfuron by 24 HAT. Addition of bentazon did not change this level of metabolism. These studies suggest that the physiological basis for the decrease of soybean injury from thifensulfuron, when it is tank-mixed with bentazon, is decreased thifensulfuron translocation.

Greenhouse and laboratory studies were conducted to determine the extent of cross-resistance of chlorsulfuron-resistant sugarbeet (CR1-B) to other herbicides that inhibit acetolactate synthase (ALS) and to determine the physiological basis of resistance. Cross-resistance to metsulfuron, imazaquin, and imazethapyr was not evident, while only marginal cross-resistance was observed to triasulfuron, DPX-L5300, and nicosulfuron. CR1-B was moderately resistant to chlorsulfuron and chlorimuron and was highly cross-resistant to thifensulfuron and primisulfuron. Further greenhouse studies demonstrated that CR1-B was not significantly injured by thifensulfuron and primisulfuron applied at or exceeding the field use rate. Studies with 14C-primisulfuron showed that differential absorption or metabolism of primisulfuron could not account for the observed resistance. ALS enzyme assays showed that the CR1-B ALS enzyme activity was 66, 26, and 13 times less sensitive to chlorsulfuron, thifensulfuron, and primisulfuron inhibition, respectively, compared to ALS enzyme extracted from sensitive sugarbeets. An altered ALS enzyme, which is less sensitive to sulfonylurea herbicide inhibition, appears to be the physiological basis of resistance.

Field studies were conducted in 1995 and 1996 at three locations in Illinois to determine soybean response to combinations of thifensulfuron and bentazon. Thifensulfuron was applied at 2.2 to 8.8 g ai/ha alone or in combination with 280 to 560 g/ha of bentazon. Soybean injury 30 d after treatment ranged from 0 to 22% when thifensulfuron was applied alone at 2.2 g/ha. Increasing thifensulfuron rate to 8.8 g/ha increased soybean injury to a range of 12 to 44%. Soybean grain yield was significantly reduced compared to the yield of untreated soybean when thifensulfuron was applied at 4.4 and 8.8 g/ha in two of five and four of five experiments, respectively. The addition of bentazon to thifensulfuron consistently reduced soybean injury and stunting. In many cases, increasing the bentazon rate to 420 g/ha decreased soybean injury from thifensulfuron to a greater extent than 280 g/ha. In cases where thifensulfuron decreased soybean yield, the addition of 420 or 560 g/ha of bentazon restored yields to levels that were not lower than untreated soybeans. These studies demonstrate that thifensulfuron at 2.2 to 8.8 g/ha in combination with bentazon at 420 g/ha may be safely applied to soybean for broadleaf weed control.

The effect of methylated seed oil (MSO), the organosilicone adjuvant DC-X2-5394, and ammonium sulfate on the efficacy, absorption, and spray retention of primisulfuron applied alone or with atrazine, dicamba, and bentazon to shattercane and giant foxtail was evaluated. Primisulfuron efficacy on both species was reduced by the three tank-mix combinations. Atrazine antagonism was not explained by decreases in foliar absorption and/or spray retention. Reductions in primisulfuron absorption and/or foliar spray retention appeared to cause bentazon antagonism on both weeds and dicamba antagonism on shattercane. MSO, DC-X2-5394, and ammonium sulfate completely reversed dicamba and bentazon antagonism on shattercane and partially reversed bentazon antagonism on giant foxtail by increasing foliar absorption and/or spray retention. Compared with non-ionic surfactant, MSO and DC-X2-5394 consistently increased giant foxtail control with primisulfuron by increasing foliar absorption and/or spray retention.

Field studies were conducted in 1994 and 1995 at Dekalb and Urbana, IL, to evaluate preemergence broadleaf weed control and crop tolerance in imidazolinone resistant (IR) and susceptible (non-IR) corn using atrazine, imazethapyr, AC 263,222, CGA-152005, MON 12000 with and without MON 13900 (a safener), and flumetsulam + clopyralid. When sufficient rainfall occurred within 28 d of application to insure herbicide absorption, the IR corn variety was more tolerant than the susceptible variety to imazethapyr, AC 263,222, CGA-152005 at 40 and 80 g/ha, and MON 12000 with and without MON 13900. Overall crop tolerance of IR corn was equal to that of corn treated with atrazine for all herbicide treatments except CGA-152005, which injured IR corn. Control of velvetleaf, common lambsquarters, Pennsylvania smartweed, tall morningglory, and jimsonweed for all herbicide treatments was equal or superior to that of atrazine at 1.7 kg/ha. However, control of common cocklebur was significantly greater with atrazine compared to imazethapyr and the low rate of CGA-152005.

Field experiments were conducted at Dekalb, IL, in 1996 and 1997 to determine the optimum application timing and rate of cloransulam for giant ragweed (Ambrosia trifida) control in soybean (Glycine max). Cloransulam treatments included preplant incorporated (PPI) and preemergence (PRE) applications of 35 g ai/ha and early postemergence (EPOST), postemergence (POST), and late postemergence (LPOST) applications of 18 or 27 g ai/ha. Cloransulam applied at 18 g/ha was also combined with lactofen at 70 g ai/ha at each POST application timing. At 60 d after LPOST, cloransulam applied PPI provided 68% giant ragweed control in 1996 and 1997 compared to PRE applications, which provided 95 and 25% giant ragweed control, respectively. The reduction in giant ragweed control with PRE applications of cloransulam in 1997 was likely due to insufficient rainfall for activation. Cloransulam applied at 18 g/ha EPOST provided 87 and 88% giant ragweed control, respectively, in 1996 and 1997. Cloransulam applied POST provided 97 and 82% giant ragweed control, respectively, in successive years. Delaying cloransulam application until LPOST reduced giant ragweed control to 53 and 47%, respectively, in 1996 and 1997 compared to EPOST and POST. At EPOST and POST application timings, increasing the rate of cloransulam to 27 g/ha or adding lactofen did not improve giant ragweed control. However, giant ragweed control was improved by at least 20% by increasing the rate of cloransulam to 27 g/ha at LPOST. Similarly, applying cloransulam in combination with lactofen improved giant ragweed control by at least 15% at LPOST.

Research was conducted in 1995 and 1996 to determine the potential for commonly used volunteer corn herbicides to control volunteer sethoxydim-resistant (SR) corn in soybean. Greenhouse studies showed that the SR corn hybrid tolerated 181 times more sethoxydim than the susceptible sister hybrid. SR corn also tolerated other acetyl CoA carboxylase (ACCase) inhibitors including fluazifop-P, quizalofop-P, and clethodim with 30 X, 27 X, and 7 × magnitudes of tolerance, respectively, compared with the susceptible hybrid. SR corn exhibited the least tolerance to clethodim, with a control rating of 50% (CR50) predicted at 28 g ai/ha. Field studies at Dekalb and Urbana, IL, showed that quizalofop-P, fluazifop-P, and fluazifop-P plus fenoxaprop at 62, 140, and 140 + 47 g ai/ha, respectively, controlled 22% or less of volunteer F2 SR corn at 30 days after treatment (DAT). Clethodim at 105, 140, and 210 g/ha consistently suppressed 23 to 70% of the volunteer SR corn. Dry weight reductions at 60 DAT showed the same general trend as the visual estimates of control. The field results confirmed the greenhouse data, which suggested SR corn had the least amount of cross-resistance to clethodim compared to other ACCase-inhibiting herbicides. In 1996, only AC 299,263 and imazethapyr plus imazaquin suppressed volunteer SR corn and prevented soybean yield loss at both locations. However, no system completely controlled volunteer SR corn.

Greenhouse, laboratory, and field studies were conducted to evaluate the potential of nonionic surfactant (NIS), crop oil concentrate (COC), methylated seed oil (MSO), and 28% urea ammonium nitrate (UAN) to enhance whole plant efficacy, absorption, and spray retention of foliar applications of isoxaflutole to giant foxtail. In greenhouse studies, isoxaflutole at 10 g ai ha−1 reduced giant foxtail growth 5%, whereas the addition of a spray adjuvant reduced giant foxtail growth at least 75%. The addition of UAN improved giant foxtail growth reduction when used in combination with isoxaflutole plus NIS. Isoxaflutole spray retention on the leaf surface was increased with an adjuvant and a further increase was observed with the addition of UAN. Isoxaflutole applied with NIS, COC, and MSO resulted in 42, 60, and 91% 14C absorption, respectively, compared to 21% absorption from isoxaflutole applied alone 24 h after treatment (HAT). Increased 14C absorption and entry into the cuticle when an adjuvant was utilized with isoxaflutole resulted in greater translocation of 14C from isoxaflutole out of the treated leaf. Significant basipetal movement from foliar applications of 14C-isoxaflutole suggests phloem mobility. In field studies, isoxaflutole applied with MSO provided greater giant foxtail growth reduction compared to isoxaflutole applied with NIS and in some cases COC. The addition of UAN to isoxaflutole did not increase whole plant efficacy in field studies. These studies indicate isoxaflutole has excellent potential to be used for control of existing giant foxtail present at the time of corn planting if an adequate adjuvant is utilized.

Greenhouse and laboratory studies were conducted to determine the effects of dicamba, atrazine, and bentazon on efficacy, foliar absorption, and translocation of MON 12000 or CGA-152005 applied to velvetleaf. The efficacy of MON 12000, CGA-152005, and a combination of CGA-152005 plus primisulfuron applied at 4.5 g ai ha−1 was similar when applied alone or with 140 g ha−1 of dicamba. However, applying these herbicides in combination with 840 or 560 g ha−1 of atrazine or bentazon, respectively, reduced velvetleaf control. Increasing the rate of MON 12000, CGA-152005, or the combination of CGA-152005 plus primisulfuron to 9 g ai ha−1 or replacing crop oil concentrate (COC) with methylated seed oil (MSO) increased velvetleaf control of the atrazine and bentazon combinations but not to levels equal to these herbicides applied alone. Dicamba had no effect on the foliar absorption and translocation of 14C from MON 12000 or CGA-152005. Atrazine had little effect on foliar absorption of 14C from MON 12000 or CGA-152005, but bentazon reduced the foliar absorption of 14C from MON 12000. Replacing COC with MSO increased the foliar absorption of 14C from MON 12000 or CGA-152005 applied alone or with dicamba or atrazine, but not with bentazon. Translocation of 14C from MON 12000 or CGA-152005 out of the treated leaves was 11 and 12%, respectively, averaged across adjuvants and sampling times. These values were reduced to an average of 3 to 4% for both MON 12000 and CGA-152005 when applied in combination with atrazine or bentazon. The majority of 14C from MON 12000 or CGA-152005 was translocated acropetally. Atrazine and bentazon significantly reduced the acropetal translocation of 14C from MON 12000 at 24 and 72 h and for CGA-152005 at 12, 24, and 72 h. The physiological basis for the observed antagonism of MON 12000 and CGA-152005 by atrazine and bentazon appears to be due to reductions in acropetal translocation of MON 12000 and CGA-152005 to velvetleaf meristems.

Field experiments were conducted in 1995 and 1996 at DeKalb and Urbana, IL, to evaluate weed management systems in glyphosate-resistant soybean planted in rows 76 cm wide. These experiments compared weed control using preemergence (PRE) herbicides followed by glyphosate or postemergence (POST) tank-mix combinations of glyphosate and acetolactate-synthase-inhibiting herbicides with glyphosate applied alone at 0.63 kg ae/ha in single or sequential applications. Overall, the use of a tank-mix partner or a PRE herbicide followed by glyphosate improved weed control compared to a single application of glyphosate. However, weed control with these treatments was not better than with sequential applications of glyphosate. Control of giant foxtail exceeded 90% for single applications of glyphosate except at DeKalb in 1995 when late emergence of giant foxtail occurred after POST applications had been made. A PRE grass herbicide or a late postemergence (LPOST) application of glyphosate was necessary for season-long control of late-emerging giant foxtail. Tank-mixing glyphosate with imazethapyr, cloransulammethyl, and CGA-277476 or applying glyphosate LPOST following these herbicides improved giant foxtail control compared with these herbicides applied alone. A single application of glyphosate controlled common lambsquarters 88% or greater in two of three trials. At Urbana in 1995, a single application of glyphosate controlled common lambsquarters 78% compared to 88 to 96% control with PRE herbicides followed by glyphosate or sequential applications of glyphosate. Velvetleaf control with a single application of glyphosate ranged from 55 to 78%. A PRE application of chlorimuron + metribuzin, cloransulammethyl, or sulfentrazone followed by glyphosate POST, as well as sequential applications of glyphosate, consistently improved velvetleaf control compared to a single application of glyphosate. In some cases, adding glyphosate to a POST application of imazethapyr or CGA-277476 improved control of velvetleaf but decreased velvetleaf control when added to cloransulammethyl.

Field studies were conducted at Dekalb, Urbana, and Brownstown, IL, in 1996 and 1997 to evaluate corn (Zea mays) injury and weed control from preemergence applications of RPA 201772 alone and tank-mixed with metolachlor, atrazine, or both. No significant corn injury from RPA 201772 was observed at any time for all experiments. Giant foxtail (Setaria faberi) control at 60 days after treatment (DAT) was variable and ranged from 47 to 93% for RPA 201772 applied alone at 105 g ai/ ha. Giant foxtail control of at least 90% was observed by applying metolachlor at 1,120 g ai/ha with 105 g/ha RPA 201772. The addition of atrazine at either 1,120 or 1,680 g ai/ha improved control of giant foxtail compared with RPA 201772 applied alone at 105 g/ha in two of the six studies. RPA 201772 applied at 105 g/ha controlled at least 88% of velvetleaf (Abutilon theophrasti), Pennsylvania smartweed (Polygonum pensylvanicum), and smooth pigweed (Amaranthus hybridus). RPA 201772 controlled 88% or less of common waterhemp (Amaranthus rudis), common ragweed (Ambrosia artemisiifolia), and common cocklebur (Xanthium strumarium). Control of these three species was 92% or greater with RPA 201772 plus atrazine. Control of common lambsquarters (Chenopodium album) was at least 96% with RPA 201772 applied alone at any rate in four of the six studies. However, common lambsquarters control was 68 and 77% for RPA 201772 applied alone at 105 g/ha at Urbana and Brownstown in 1997, respectively, where high common lambsquarters densities were prevalent. Under these conditions, the addition of atrazine to RPA 201772 at 105 g/ha improved control of common lambsquarters. RPA 201772 has excellent potential to provide consistent control of velvetleaf compared with atrazine. In contrast, these studies indicate RPA 201772 may provide inconsistent control of certain weed species in different environments. In order to achieve consistent control of a broad spectrum of weed species, RPA 201772 must be combined with other herbicides.

Greenhouse and laboratory experiments were conducted to evaluate foliar absorption, translocation, and efficacy of glufosinate on four weed species. The rate of glufosinate required to reduce shoot dry weight by 50% (GR50) varied between weed species. GR50 values for giant foxtail, barnyardgrass, velvetleaf, and common lambsquarters were 69, 186, 199, and 235 g ai ha−1, respectively. Absorption of 14C-glufosinate increased with time and reached a plateau 24 hours after treatment (HAT). Absorption of 14C-glufosinate was 67, 53, 42, and 16% for giant foxtail, barnyardgrass, velvetleaf, and common lambsquarters, respectively. Translocation of absorbed 14C-glufosinate from the treated leaf was greatest for giant foxtail and barnyardgrass (15 and 14% 24 HAT of absorbed 14C-glufosinate, respectively). This compared to 5 and < 1% for translocation of absorbed 14C-glufosinate from the treated leaves of velvetleaf and common lambsquarters. The majority of 14C-glufosinate translocated by giant foxtail and barnyardgrass was found below the treated leaf and in the roots, indicating phloem mobility of the herbicide. Differential absorption and translocation of 14C-glufosinate may be contributing factors to the differential sensitivity observed between weed species.

Field studies were conducted at Dekalb and Urbana, IL, in 1995 and 1996 to evaluate the effectiveness of sethoxydim for giant foxtail control in sethoxydim-resistant (SR) corn. Experiments studied sequential and total postemergence applications of grass herbicide standards compared to sethoxydim. Additional studies evaluated the compatibility of sethoxydim with postemergence broadleaf herbicides. Metolachlor plus atrazine and metolachlor followed by dicamba plus atrazine gave at least 88% control of giant foxtail at both locations in both years. Metolachlor plus flumetsulam plus clopyralid provided 90% or greater grass control over all experiments, with the exception of only 75% control at Dekalb in 1995 due to a heavy giant foxtail infestation. In comparison, flumetsulam plus clopyralid followed by postemergence applications of sethoxydim or nicosulfuron provided the same level of grass control as preemergence metolachlor, except at Dekalb in 1995 where control was 72% for both sethoxydim and nicosulfuron. Sequential applications of sethoxydim increased control of giant foxtail compared to a single sethoxydim application in 1995. Sethoxydim applied alone controlled giant foxtail 8% better than nicosulfuron at Urbana in 1996. Postemergence sethoxydim applied alone provided 87% or better control of giant foxtail. Sethoxydim performance was consistent when applied with flumetsulam plus clopyralid plus 2,4-D (NAF-73), halosulfuron plus dicamba, and bromoxynil. The efficacy of sethoxydim was reduced in combination with dicamba plus atrazine in three of the four trials, and bentazon plus atrazine as well as primisulfuron plus prosulfuron in all trials. Sethoxydim outperformed nicosulfuron in combinations with bromoxynil at Urbana. These studies indicate sethoxydim has excellent potential to be used in corn for postemergence control of giant foxtail.

Greenhouse and laboratory studies were conducted to determine the effect of atrazine on efficacy, absorption, translocation, and metabolism of primisulfuron applied to velvetleaf and giant foxtail. Efficacy of primisulfuron was reduced by 18 and 22% when applied at 20 and 40 g ai ha−1, respectively, in combination with 1.7 kg ai ha−1 atrazine to velvetleaf. Efficacy of primisulfuron was reduced by 15 and 16% when applied at 30 or 60 g ai ha−1, respectively, in combination with 1.7 kg ai ha−1 atrazine to giant foxtail. Foliar absorption of 14C-primisulfuron by either weed species was not affected by addition of atrazine to the treatment solution. Atrazine had no effect on metabolism of 14C-primisulfuron by either weed species. In the absence of atrazine, translocation of absorbed 14C from primisulfuron out of treated leaves of velvetleaf and giant foxtail averaged 19 and 29%, respectively, across sampling times. These values were reduced to an average of 9 and 16% in velvetleaf and giant foxtail, respectively, when 14C-primisulfuron was applied in combination with atrazine. The majority of translocated 14C from primisulfuron was transported acropetally in velvetleaf and basipetally in giant foxtail. Atrazine significantly reduced 14C translocation from primisulfuron to these meristematic sinks in both weed species. Reduced translocation was positively correlated with reduced control of these weeds when primisulfuron was tank mixed with atrazine.

Studies were conducted in New Jersey and Virginia to evaluate the response of ‘Aurora Gold’ hard fescue, which had undergone five cycles of phenotypic recurrent selection for increased glyphosate tolerance, to direct applications of glyphosate. ‘Discovery’ hard fescue, which had not undergone recurrent selection, was also included in the study. Glyphosate treatments were initiated in early/mid-May and applied once, twice, or three times at 4- to 5-wk intervals at rates ranging from 0.1 to 1.6 kg ae/ha. Aurora Gold was more tolerant to glyphosate than Discovery in all experiments, indicating that recurrent selection was successful in increasing glyphosate tolerance in hard fescue. Single applications of glyphosate at rates ranging from 0.6 to 0.8 kg/ha could be applied to Aurora Gold with minimal injury or stand thinning (<20%), whereas multiple applications of glyphosate could be applied at rates ranging from 0.4 to 0.6 kg/ha. The use of Aurora Gold in areas planted to hard fescue, such as golf course roughs, vineyards, orchards, and landscapes, would allow the integration of direct glyphosate applications into an overall weed management program providing potential economic and environmental benefits.

Field experiments were conducted over 3 yr at three locations in Illinois to evaluate the efficacy of glyphosate in glyphosate-resistant soybean planted in rows spaced 19, 38, and 76 cm. Minimal soybean injury (less than 10%) was observed from any glyphosate treatment. Glyphosate treatments controlled 82 to 99% of giant foxtail. Common waterhemp control was increased as soybean row spacing was decreased. Applying sequential glyphosate applications or increasing the glyphosate rate from 420 g ae/ha to 840 g/ha frequently increased common waterhemp control in 76-cm rows. Velvetleaf control with glyphosate was variable, ranging from 48 to 99%. Decreasing soybean row spacing, utilizing sequential glyphosate applications, or increasing the glyphosate rate improved velvetleaf control in at least four of eight site-years. Glyphosate treatments generally resulted in weed control and soybean yield equal to or greater than the standard herbicide treatments. However, glyphosate treatments yielded less than the hand-weeded control in four of eight site-years, suggesting that weed control from glyphosate treatments was sometimes inadequate.