Studies were conducted from 1992 to 1995 to determine the effect of rimsulfuron on corn spurry, wild radish, narrowleaf goldenrod, and quackgrass and potato cultivars. Rimsulfuron alone gave 100% control of wild radish, 68 to 70% control of corn spurry, and 75 to 90% control of narrowleaf goldenrod. Rimsulfuron plus metribuzin gave 99 to 100% control of wild radish and 85 to 100% control of corn spurry. Quackgrass control varied from 51 to 90% between experiments, indicating that environmental and plant factors affected the activity of the herbicide. Tank mixes with metribuzin slightly reduced the control of quackgrass but resulted in greater foliar injury than that of rimsulfuron to potato. Slight injury to potato plants disappeared within 2 to 3 wk, and tuber yields were not reduced. Russet Burbank, Shepody, and Kennebec potato cultivars had slight (2 to 8%) injury from rimsulfuron. Injury to Shepody (14 to 20%) and Russet Burbank (11%) increased when rimsulfuron was applied with metribuzin. Rimsulfuron had no effect on the number or the fresh weight of sprouts on daughter tubers tested the next spring after application.

Field trials were conducted at two sites in both 1997 and 1998 to evaluate soybean response and weed control with glufosinate alone or combined with quizalofop, lactofen, imazethapyr, flumiclorac, or bentazon plus acifluorfen in narrow-row, glufosinate-resistant soybean. Soybean injury ranged from 0 to 21% at 2 wk after treatment (WAT) and from 0 to 5% by 4 WAT. Glufosinate alone at 0.29 and 0.4 kg ai/ha controlled velvetleaf, common waterhemp, common ragweed, morningglory species, and giant foxtail greater than 85% in all studies. Mixtures containing glufosinate and other herbicides controlled these species greater than 81% but did not improve control over glufosinate alone. Estimates of weed biomass closely reflected visual control evaluations. However, giant foxtail biomass was higher for mixtures of glufosinate plus lactofen, flumiclorac, or bentazon and acifluorfen, indicating possible antagonism of glufosinate activity. At both locations, soybean yields were similar among most treatments, but that of the glufosinate plus lactofen treatment was lower when compared with other treatments. Additional trials evaluated soybean response and weed control with a preemergence herbicide followed by glufosinate postemergence (POST), glufosinate applied once or twice POST, and mixtures of glufosinate plus imazethapyr or flumiclorac POST in wide-row soybean. Glufosinate applied twice controlled common waterhemp, morningglory species, prickly sida, common cocklebur, and giant foxtail up to 39% greater than did glufosinate applied once. The addition of imazethapyr, but not flumiclorac, to glufosinate improved weed control when compared with glufosinate alone.

Weed management strategies are needed to control weeds in corn that emerge after postemergence (POST) application of glyphosate or glufosinate. Field trials were conducted from 1996 to 1999 to determine if residual herbicides could be used with glyphosate or glufosinate to provide season-long weed control in glyphosate-resistant or glufosinate-resistant corn. Preemergence (PRE) applications of several residual herbicides followed by POST applications of glyphosate or glufosinate were compared with POST tank mixtures of glyphosate or glufosinate with residual herbicides. All residual herbicides used in combination with glyphosate, when compared with glyphosate alone, increased control of redroot pigweed and common lambsquarters by an average of 20% and resulted in a 4 to 19% increase in control of giant foxtail. Each residual herbicide tank mixture with glufosinate, when compared with glufosinate alone, increased control of common ragweed and giant foxtail. In most instances, weed control was similar for total POST and for PRE followed by POST systems. Velvetleaf control was reduced by 12% when glyphosate was tank mixed with a half rate of atrazine compared with a full rate of atrazine. Common lambsquarters control was reduced by 13% when glyphosate was tank mixed with a half vs. a full rate of acetochlor. Glufosinate tank mixed with half rates of acetochlor + atrazine, flumetsulam, or pendimethalin reduced control of velvetleaf compared with the full rate of these products. Corn yields were not affected by residual herbicide application timings or rates of residual herbicides.

Field and greenhouse studies were conducted to evaluate herbicides in pumpkin. Field experiments at three Illinois locations determined weed control and crop injury from clomazone, dimethenamid, ethalfluralin, sulfentrazone, imazamox, RPA 201772, flumiclorac, and halosulfuron applied preemergence. Clomazone plus sulfentrazone controlled redroot pigweed 78 to 99%, ivyleaf morningglory 80 to 97%, common lambsquarters 97%, common purslane 84 to 99%, and velvetleaf 55 to 99%. Imazamox plus clomazone commonly provided more consistent broadleaf weed control than did ethalfluralin plus clomazone. RPA 201772 when used on sandy soils killed the pumpkin. Sulfentrazone initially caused chlorosis and necrosis on pumpkin seedlings when soil organic matter was low (< 1%) or when soil moisture was high. However, plants recovered rapidly, and yields were not affected. In a greenhouse study pumpkin was more tolerant to clomazone plus sulfentrazone than to sulfentrazone.

Field studies were conducted at three sites in Delaware from 1997 to 1999 to evaluate fall glyphosate applications followed by postemergence (POST) field corn herbicides on horsenettle control and shoot densities. The fall treatments were either no fall treatment or 2.2 kg ai/ha glyphosate as a preharvest treatment in soybean at least 2 wk prior to frost. POST treatments were applied the following spring in no-tillage field corn 4 wk after planting (WAP) and included glyphosate, CGA 152005 plus primisulfuron plus dicamba, halosulfuron plus dicamba, atrazine plus dicamba, nicosulfuron plus rimsulfuron plus atrazine plus dicamba, or nicosulfuron plus dicamba. The fall glyphosate application delayed horsenettle shoot emergence in the spring and resulted in > 90% control at the time of POST in-crop applications. At 11 WAP, the highest horsenettle control was observed with a fall glyphosate application followed by POST in-crop treatments of CGA 152005 plus primisulfuron plus dicamba, halosulfuron plus dicamba, or nicosulfuron plus rimsulfuron plus dicamba and no fall treatment followed by CGA 152005 plus primisulfuron plus dicamba.

Two field studies evaluating horsenettle control were conducted from 1997 to 1999 to examine the efficacy of various fall-applied herbicides and rates and to evaluate the effect of the stage of horsenettle senescence on the effectiveness of fall glyphosate applications. The herbicides and rates evaluated in the fall herbicide efficacy study included 1.1, 2.2, or 3.4 kg ai/ha glyphosate, 1.7, 2.2, or 3.4 kg ai/ha glyphosate-trimesium, 0.6, 1.1, or 2.2 kg ai/ha dicamba, 0.06 plus 0.16, 0.09 plus 0.2, or 0.17 plus 0.44 kg ai/ha BAS 654 plus dicamba, respectively, or 2.2 kg ai/ha glyphosate plus 0.6 kg ai/ha dicamba. The highest horsenettle control in the following spring was observed with all rates of glyphosate or glyphosate-trimesium, the highest rate of BAS 654 plus dicamba, or glyphosate plus dicamba. In the study on the horsenettle stage of senescence, 2.2 kg ai/ha glyphosate was applied at stages of senescence in the fall. The presenescence stage reduced horsenettle shoot density from fall to spring and provided the highest level of control in June and July of the following year compared with plants that had already begun leaf color change and leaf drop.

Diminished control of goosegrass was observed in tomato fields located in Manatee County, FL, after years of repeated paraquat use. Tolerance of the Manatee biotype to paraquat was confirmed by its comparison in greenhouse studies with a susceptible biotype from the Alachua County, FL. A 30-fold increase in paraquat rate was required to reach the 50% growth reduction level of the resistant biotype over the susceptible biotype. The Manatee biotype was not tolerant to clethodim, metribuzin, or sethoxydim. These herbicides provided adequate control of all the goosegrass biotypes tested.

Crop response to carfentrazone–ethyl can be affected by environmental conditions. Field research was initiated to determine the effect of irrigation and light intensity prior to herbicide treatment on crop response to carfentrazone–ethyl. Wheat, corn, and soybean response was evaluated in 1996 and 1997, 2 yr that differed significantly in rainfall. It was difficult to distinguish differences in visible crop injury between irrigated and nonirrigated crops within the same year; however, injury was much higher in 1996 than in 1997. In 1996, the study area received timely rainfall prior to treatment of each crop, but in 1997, no precipitation was recorded during the treatment period. Overall, irrigated plants appear to be slightly more sensitive than nonirrigated plants. In contrast, crop injury was significantly higher in response to low light intensity prior to herbicide treatment. Soybean plants covered with 80% shade cloth for 5 d prior to carfentrazone–ethyl application were injured 24 to 41% more than nonshaded plants. Corn was relatively insensitive to either condition. Soybean plants were very sensitive to carfentrazone–ethyl and were highly influenced by both light intensity and irrigation. Wheat response to carfentrazone–ethyl was not influenced within 1 yr by irrigation, but injury in 1996 was four times higher than in 1997. Light intensity prior to treatment influenced wheat response to carfentrazone–ethyl, where shading before treatment increased visible injury in wheat, but by less than 10%. The risk of crop injury increases when carfentrazone–ethyl is applied to irrigated plants or to crops following several cloudy days.

Field experiments were conducted in 1998 and 1999 at two locations in Mississippi to determine weed control efficacy of postemergence soybean herbicides alone or following pendimethalin + imazaquin preemergence in glufosinate-tolerant soybean planted in 38- or 76-cm rows. Glufosinate applications controlled pitted morningglory better than conventional herbicide treatments, regardless of row spacing. Pendimethalin + imazaquin did not increase the efficacy of glufosinate on pitted morningglory. Pitted morningglory control was increased in narrow rows when compared to wide rows with all treatments. Sicklepod control ranged from 90 to 100% in narrow rows with glufosinate, regardless of rate. Residual herbicides alone controlled sicklepod 54%, regardless of row spacing. With grass species, two applications of 420 g ai/ha glufosinate controlled weeds 82 to 100%. Residual herbicides followed by 420 g/ha glufosinate controlled grass species 80% or more, regardless of row spacing. Hemp sesbania control ranged from 80 to 92% in 76- and 38-cm rows with one application of 560 g/ha glufosinate. Glufosinate at 420 g/ha used as sequential applications controlled hemp sesbania better than the conventional treatment in 76-cm rows. Residual herbicides in combination with glufosinate did not increase hemp sesbania control. There were no differences in yield due to row spacing at Stoneville in either year due to extremely dry growing conditions during pod set. At Starkville, two applications of 420 g/ha glufosinate resulted in higher yields than pendimethalin + imazaquin followed by 420 g/ha glufosinate in both years. Pendimethalin + imazaquin followed by 420 g/ha glufosinate increased yield in narrow rows compared to wide rows at Starkville in 1998.

Field studies were conducted in 1998 and 1999 to evaluate the efficacy of glufosinate on Palmer amaranth, redroot pigweed, and common waterhemp at different growth stages in soybean planted at early, normal, and late dates. At 2, 4, and 8 wk after treatment, common waterhemp control was greater than Palmer amaranth and redroot pigweed control with single glufosinate applications of 410 g ai/ha at 2- to 5-, 7- to 10-, or 15- to 18-cm Amaranthus height or with two sequential applications of 293 g/ha at 2- to 5-cm height and 2 wk later. Only the sequential applications of 410 and 293 g/ha resulted in more than 80% control of Palmer amaranth and redroot pigweed, but all five treatments controlled common waterhemp more than 80%. All glufosinate treatments reduced the dry weight of all Amaranthus species by more than 65%. However, the sequential applications resulted in the greatest dry weight reductions.

Field observations in Ohio suggested a possible interaction between soybean cyst nematode (SCN) and glyphosate in Countrymark 316 soybean, a transgenic glyphosate-resistant (R) variety that also expresses SCN resistance derived from ‘PI88788’ soybean. To investigate this possible interaction under controlled conditions, greenhouse experiments were conducted in which Countrymark 316 (R) and Corsoy 79 (S = susceptible to glyphosate and SCN) soybean root and shoot weights were measured in response to three concentrations of race 3 SCN inoculum and five glyphosate doses. Experiments were conducted in which glyphosate was applied 9, 18, or 27 d after inoculation (DAI). Data from SCN treatments in the (S) soybean experiments were regressed on glyphosate dosage and fit to a log-logistic dose–response model. SCN–glyphosate interaction in the (S) soybean variety reduced root dry weight of SCN-inoculated plants 6% compared with noninoculated plants when 1.0 kg/ha glyphosate was applied 18 DAI. The most significant interaction of SCN and glyphosate in the (S) variety occurred when glyphosate was applied 27 DAI; the glyphosate dose required to reduce shoot fresh weight 25% was 0.55 kg/ha in the noninoculated control compared with 0.32 kg/ha in plants inoculated with 1,000 SCN eggs/200 cm3 soil. Glyphosate rates of 0.84 and 1.69 kg/ha reduced root dry weights of Countrymark 316 (R) soybean 10 to 13% at the 18 DAI application timing only. Inoculation with SCN reduced shoot fresh weight of (R) soybean 8 to 29% across all experiments, but there was no interaction of glyphosate and SCN in (R) soybean.

A 2-yr field study was conducted to evaluate the response of rice to rotational crop herbicides in combination with rice herbicides in water-seeded culture. Fluometuron, imazethapyr, metolachlor, and norflurazon were applied at 0.5, 0.25, 0.125, and 0.063 times the recommended use rates preplant incorporated (PPI) to simulate herbicide carryover from previous crops. Molinate and thiobencarb at 4.5 kg ai/ha were applied PPI, and quinclorac at 0.43 kg ai/ha postemergence. No interaction between rice herbicides and rotational crop herbicides was observed for rice injury at 4 wk after planting (WAP), plant dry weight, stand, and height at 8 WAP, or rice grain yield. However, rice heading was delayed with some rotational crop herbicide and rice herbicide combinations. Fluometuron at the 0.5 and 0.25× rates injured rice 64 and 21% at 4 WAP, and reduced rice yield 96 and 20%, respectively. At 4 WAP, metolachlor at the 0.5 and 0.25× rates injured rice 93 to 29%, and reduced rice yield 85 to 20%, respectively. An 84 to 100% rice injury at 4 WAP and a 81 to 100% rice yield reduction were observed with norflurazon at the 0.5 and 0.25× rates, respectively. Imazethapyr caused 15 to 26% rice injury 4 WAT and 22 to 41% yield reduction.

Field trials were conducted during 1998 and 1999 to evaluate the effects of sequential herbicide treatment, herbicide application timing, and mowing on mugwort control. In the first field trial dicamba, triclopyr, clopyralid, picloram, metsulfuron, glufosinate, glyphosate, and the dimethylamine salt and the isooctyl ester of 2,4-D were applied to mugwort at 7-wk intervals to evaluate mugwort control after one, two, and three herbicide applications. When applied in three sequential applications, all herbicides except triclopyr, metsulfuron, and glufosinate provided at least 70% mugwort control 1 yr after treatment (YAT). At least 70% mugwort control was also achieved with just two sequential applications of dicamba, and only one application of picloram or clopyralid provided 100 and 84% mugwort control 1 YAT, respectively. In the second field trial the influence of application timing was investigated by applying herbicides to mugwort in the vegetative and the flowering stages of growth. Additionally, the effect of sequential mowing was evaluated by applying herbicides to mugwort regrowth after either one or two mowings. Generally, there was no difference in the level of mugwort control achieved with applications of these herbicides to mugwort in the flowering vs. the vegetative stage of growth. However, when averaged over all the herbicides included in these trials, two sequential mowings conducted before herbicide application enhanced the control of mugwort compared with either unmowed mugwort or mugwort that had been mowed once before herbicide application. Additionally, with the exception of picloram and glyphosate, all the herbicides evaluated in these trials provided higher mugwort control when applied to unmowed mugwort compared with mugwort that had been mowed only once. The results from these trials indicate that sequential herbicide treatment and sequential mowing are strategies that will enhance the control of mugwort when used with the majority of herbicides evaluated in these trials.

Sclerotinia stem rot is an important soybean disease. An increase in phytoalexin production with herbicide treatments may reduce the incidence of this disease in soybean. Research was conducted to determine soybean response, Sclerotinia sclerotiorum lesion development, and phytoalexin production in glyphosate-resistant and -susceptible soybean cultivars treated with protoporphyrinogen oxidase–inhibiting herbicides. Necrosis of soybean leaves 7 d after postemergence application of oxyfluorfen at 17.5 g ai/ha, carfentrazone at 1.8 g ai/ha, sulfentrazone at 9.0 g ai/ha, fomesafen at 280 g ai/ha, acifluorfen at 425 g ai/ha, flumiclorac at 30 g ai/ha, CGA-248757 at 4 g ai/ha, and oxadiazon at 280 g ai/ha was equal to or less than lactofen at 70 g ai/ha. In a detached leaf bioassay, S. sclerotiorum lesion diameter was reduced by oxyfluorfen, carfentrazone, sulfentrazone, lactofen, fomesafen, flumiclorac, and oxadiazon compared with the untreated control. Furthermore, lesion diameter on untreated leaves of soybean treated with oxyfluorfen, carfentrazone, sulfentrazone, lactofen, fomesafen, acifluorfen, flumiclorac, CGA-248757, and oxadiazon was reduced compared with the untreated control. Lactofen and sulfentrazone increased leaf phytoalexin production similarly, but neither herbicide affected stem phytoalexin production compared with the untreated control. Glyphosate-resistant and near-isogenic–susceptible cultivars responded similarly when inoculated with S. sclerotiorum in the detached leaf bioassay. Glyphosate-resistant S20-B9 and P93B01 produced more phytoalexins than glyphosate-susceptible S 19-90 and P9281. Herbicide treatments may increase phytoalexin production in leaves of treated plants, but levels in the stem do not explain protection from Sclerotinia stem rot.

Greenhouse and field research was conducted to determine the effect of glufosinate, glyphosate, and glyphosate plus additional adjuvant on yellow nutsedge control and tuber production. Glyphosate at 0.84 kg/ha reduced yellow nutsedge dry weight 64%, whereas glufosinate at 0.4 kg/ha reduced dry weight only 22% when averaged over diammonium sulfate (DAS) and spray volume. Furthermore, yellow nutsedge dry weight was reduced 53% in the presence and 34% in the absence of DAS; however, dry weights were similar when spray volumes of glufosinate or glyphosate ranged from 140 to 1038 L/ha. Yellow nutsedge control with glyphosate and glufosinate increased to 88 and 68%, respectively, when the herbicides were injected into the plant. In the field, glufosinate at 0.4 kg/ha and glyphosate at 0.84 kg/ha controlled yellow nutsedge 19 and 53%, respectively. Glyphosate reduced yellow nutsedge tuber density 51%, tuber fresh weight 59%, and tuber sprouting 17% 42 wk after treatment in the field. The addition of nonionic surfactant, methylated seed oil, or crop oil concentrate to glyphosate plus DAS did not increase yellow nutsedge control with glyphosate in the greenhouse or field.

Competition from annual grasses and yellow starthistle can severely reduce perennial grass forage production and quality in pasture and rangeland. The purpose of this study was to determine yellow starthistle and weedy annual grass control by imazapic applied alone or in combination with picloram, and smooth brome tolerance to these treatments. Sixty days after treatment (DAT) imazapic applied at 70 and 140 g ae/ha reduced annual grass (downy brome, medusahead, and annual bluegrass) plant density and biomass by 66 to 76% compared with the untreated control. Picloram applied at 280 and 420 g ae/ha reduced yellow starthistle plant density and biomass by over 93%. Imazapic applied at 70 and 140 g/ha reduced smooth brome biomass by 79 to 95% at 60 DAT. Picloram did not affect the density or the biomass of annual grasses or smooth brome, whereas imazapic did not markedly affect the density or the biomass of yellow starthistle. Downy brome control increased to a maximum of 97% with increasing imazapic dose (maximum of 280 g/ha) at 30, 60, and 90 DAT.

Field studies were conducted in 1999 and 2000 at Belleville, IL, to compare herbicide efficacy and economic return on investment (EROI) for various herbicide systems in conventional, imidazolinone-resistant, glufosinate-resistant, and glyphosate-resistant corn hybrids. Corn injury 14 d after RPA 201772 preemergence (PRE) treatments ranged from 0 to 10%. Treatments with nicosulfuron + rimsulfuron + atrazine injured corn 5 to 24% at 7 d after treatment (DAT); however, no injury was visible at 14 DAT. Corn injury by all herbicide treatments dissipated by 28 DAT. All treatments controlled giant foxtail at least 88%. Common waterhemp was controlled at least 94% with all treatments, except for imazethapyr + imazapyr postemergence (POST), which did not control common waterhemp. All treatments controlled at least 92% of common cocklebur, giant ragweed, and ivyleaf morningglory, with the exception of the total PRE herbicide system of S-metolachlor + atrazine in 2000. Average grain yield ranged from 7,290 to 9,180 kg/ha in 1999, with the yield of the glyphosate-resistant hybrid lower than that of all other hybrids. In 2000, average grain yield ranged from 8,440 to 11,520 kg/ha, with the grain yield of the glyphosate-resistant hybrid greater than that of all other hybrids. There were no differences in economic return in 1999 because of the treatment, the herbicide system, or the hybrid. In 2000 EROI was greater with the glyphosate-resistant hybrid than with the other hybrids. EROI was influenced more by the grain yield of the corn hybrid than by the associated weed control costs. It has been demonstrated by this research that effective and economical weed control can be achieved in all hybrids, with minimal injury.

Potassium azide (PA) (112 kg/ha), oxadiazon + 1,3-dichloropropene (1,3-D) (168 kg/ha + 140 L/ha), dazomet (392 kg/ha), dazomet + chloropicrin (392 + 168 kg/ha), dazomet + 1,3-D (392 kg/ha + 140 L/ha), iodomethane (IM) (336 kg/ha), metam-sodium (MS) (748 L/ha), MS + chloropicrin (748 L/ha + 168 kg/ha), and MS + 1,3-D (748 + 140 L/ha) were evaluated at Jay and Arcadia, FL, in 1998 and 1999 as alternatives to methyl bromide (MeBr) fumigation for the management of common turfgrass weeds. Potassium azide was as effective as MeBr in controlling ‘Coastal’ bermudagrass, yellow and purple nutsedges, alexandergrass, broadleaf signalgrass, tall and sharppod morningglories, and various winter annual broadleaf weeds, but it failed to provide acceptable control of redroot pigweed. 1,3-Dichloropropene + oxadiazon did not control yellow nutsedge, purple nutsedge, or Coastal bermudagrass. Similarly, this combination treatment failed to control carpetweed but did provide 83% control of the winter annual weed species, 71% control of alexandergrass and broadleaf signalgrass, and ≥ 80% control of tall morningglory, sharppod morningglory, and redroot pigweed. Dazomet + combination treatments provided control of Coastal bermudagrass at Jay; however, control of common bermudagrass, alexandergrass, and broadleaf signalgrass was not acceptable at Arcadia. Sedge species control with dazomet + combinations was poor (< 63%) at both sites. Iodomethane, a treatment not yet registered by the U.S. Environmental Protection Agency (EPA), controlled weedy grass species, sedge species, and broadleaf weeds present at the two locations under different environmental conditions. Metam-sodium alone and MS + chloropicrin, tarped and untarped, and MS + 1,3-D provided acceptable weed control; however, MS + chloropicrin covered with a plastic tarp for 48 h was the best MS treatment. Metam-sodium + chloropicrin, with plastic tarp, controlled weedy grass and broadleaf species equal to MeBr; however, unacceptable sedge species control at Jay and Arcadia was 56 and 79%, respectively. Metam-sodium applied alone failed to control redroot pigweed; however, MS + combinations provided control. These studies confirm that no EPA-registered fumigant alternative to MeBr, applied alone or in combination for preplant turf soil fumigation, exists. Consequently, until such time that an effective alternative is identified, turf managers will be forced to forego fumigation, or they will have to choose a less-effective alternative and accept the consequences of contamination.

Field studies were conducted in 1999 and 2000 at Belleville, IL, to evaluate herbicide efficacy, grain yield, and economic return on investment (EROI) from various herbicide systems in conventional, sulfonylurea-tolerant, glufosinate-resistant, and glyphosate-resistant soybean varieties. Several grower-oriented herbicide systems were developed within each soybean variety using current weed control options. These herbicide systems included herbicides with soil-residual, herbicides with different modes of action, and combinations of preemergence (PRE) followed by (fb) postemergence (POST) herbicides. Soybean injury ranged from 1 to 16% 28 d after (DA) PRE applications of sulfentrazone plus chlorimuron plus pendimethalin. Injury 7 DA POST treatments ranged from 2 to 39%, with the greatest injury occurring from the conventional herbicide combination of fomesafen plus fenoxaprop plus fluazifop-P. No injury symptoms persisted through soybean harvest. Control of giant foxtail was the most consistent (97% or greater) in the PRE broadleaf fb POST herbicide system 56 DA planting. Common waterhemp control was at least 85% for all treatments, with the exception of the single POST herbicide systems of chlorimuron plus thifensulfuron plus quizalofop-P, and glufosinate and the standard sequential herbicide system of pendimethalin fb chlorimuron plus thifensulfuron. All treatments provided at least 87% control of common ragweed and ivyleaf morningglory. Soybean grain yield was similar between varieties in the weed-free control plots in 1999. In 2000, grain yield of the glyphosate- and glufosinate-resistant soybean varieties was greater than for the conventional and sulfonylurea-tolerant varieties. Overall, soybean grain yield and EROI were less for some treatments because of poor control of common waterhemp. Weed control had a greater influence than herbicide-related costs on EROI.

Greenhouse studies verified that smooth crabgrass from a golf course tee in southern New Jersey was resistant to fenoxaprop-P, although smooth crabgrass from a nearby untreated rough was susceptible to this herbicide. Fenoxaprop-P-resistant plants were injured, however, when fenoxaprop-P was applied at levels above the maximum use rate for turf. Fenoxaprop-P applied postemergence at 0.76 kg ai/ha, four times the maximum rate, reduced shoot weight of the resistant biotype by 35%, whereas application of 1.52 kg/ha, eight times the maximum rate, reduced shoot weight by 64%. Large crabgrass and the susceptible biotype of smooth crabgrass were controlled by fenoxaprop-P applied at 0.1 kg/ha. Fenoxaprop-susceptible and -resistant biotypes of smooth crabgrass had a similar response to MSMA, dithiopyr, and quinclorac applied postemergence. The fenoxaprop-P–resistant smooth crabgrass biotype was controlled by the cyclohexanedione herbicides sethoxydim and clethodim, but the aryloxyphenoxypropionate herbicides fluazifop and quizalofop reduced shoot weight by only 15 to 66% depending on herbicide and rate.