The effects of ammonium sulfate and pelargonic acid on weed control with glufosinate and glyphosate and safety to glufosinate-resistant and glyphosate-resistant soybean were investigated in the greenhouse and field. Annual and perennial weeds varied in their sensitivity to the herbicides. Based on fresh weight reduction 10 d after treatment (DAT), common milkweed was more tolerant to glufosinate, and horsenettle was more tolerant to glyphosate. Giant foxtail was highly sensitive to both herbicides. The activity of glufosinate on common milkweed and of glyphosate on horsenettle was enhanced with the addition of 5% (wt/v) ammonium sulfate. The addition of pelargonic acid at 3% (v/v) did not enhance the activity of glufosinate or glyphosate on any weed, and it antagonized common lambsquarters and giant foxtail control with glufosinate and with glyphosate. Glyphosate was more effective than glufosinate in suppressing the regrowth of the perennial weeds horsenettle and common milkweed, but addition of ammonium sulfate and pelargonic acid was not beneficial with either herbicide. Under field conditions, the addition of ammonium sulfate or pelargonic acid to glufosinate or glyphosate did not improve efficacy on annual weeds. The addition of pelargonic acid improved yellow nutsedge control with glufosinate, but only at 6 DAT. Glufosinate and glyphosate applied alone or in combination with ammonium sulfate were safe to transgenic soybeans resistant to the respective herbicide. The addition of pelargonic acid to glufosinate or glyphosate in the greenhouse caused a rate-dependent reduction in soybean fresh weight. In the field, slight soybean injury with the addition of pelargonic acid was evident 6 DAT, but not 23 DAT. Addition of ammonium sulfate can increase the efficacy of glufosinate and glyphosate on perennial weeds without negatively affecting soybean yield.

An isolate of the fungus Dactylaria higginsii obtained from purple nutsedge in Florida was highly pathogenic to Cyperus spp. The potential of this isolate as a bioherbicide was field tested in natural populations of purple nutsedge in Gainesville and Jay, FL. The fungus was applied in 0.5% Metamucil® as a carrier, and the treatments were: carrier only, 105 conidia/ml + carrier, and 106 conidia/ml + carrier. Treatments were applied as single, double, or triple postemergence (POST) sprays at biweekly intervals. The disease and secondary infections developed in about 5 and 15 d after inoculation, respectively, killing most of the infected leaves. All weed growth parameters and disease progress rates were affected by inoculum dosage and inoculation frequencies. Three inoculations, each at 106 conidia/ml, provided effective control of purple nutsedge compared to a single inoculation, as measured by shoot dry weight, tuber numbers, and tuber dry weight. Higher rates of disease progress and disease levels, defined by the area under the disease progress curve (AUDPC), occurred with three inoculations at 106 conidia/ml. Disease progress was slower and the level of weed control was lower at 105 conidia/ml compared to the higher inoculum level. Three applications of 106 conidia/ml provided >90% nutsedge control. Dactylaria higginsii appears to be an effective bioherbicide candidate deserving further development for commercial use.

Greenhouse and growth chamber experiments were conducted to study glyphosate efficacy, rainfastness, absorption, and translocation in redvine. Glyphosate at 0, 0.56, 1.12, 2.24, and 4.48 kg ai/ha was applied to redvine plants raised from rootstocks at the five- to seven-leaf stage (about 25 cm tall). Redvine control ranged from 55% at 0.56 kg/ha glyphosate to 98% at 4.48 kg/ha. Glyphosate at rates above 1.12 kg/ha, greatly reduced regrowth from rootstocks of treated plants. A simulated rainfall of 2.5 cm (7.5 cm/h intensity) within 24 h of glyphosate application reduced efficacy by 23% compared with no simulated rainfall. Absorption of 14C-glyphosate in redvine increased from 1.8 to 21.9%, and translocation increased from 0.1 to 8.1% from 6 to 192 h after application, respectively. Translocation was both acropetal and basipetal, and by 96 h of exposure, the 14C radioactivity was widely distributed throughout the plant. Absorption and translocation was greatly affected by posttreatment temperature. Absorption and translocation were highest (34.9 and 10.6%, respectively) in plants maintained at 35/30 C (14/10 h, day/night), followed by 15/10 C (21.2 and 4.9%, respectively), and was lowest (7.8 and 1.6%, respectively) in plants maintained at 25/20 C. Results suggest that longer periods of leaf exposure to the herbicide and high temperatures could increase glyphosate absorption, translocation to redvine rootstocks, and subsequent control. These data also suggest that effective control of redvine in the field will require glyphosate rates higher than those recommended for use in glyphosate-resistant crops.

Studies were conducted in 1996 and 1997 to determine the effect of irrigation systems used to produce transplants on subsequent tolerance of banana and bell pepper (Capsicum annuum) transplants to field-applied herbicides. The irrigation systems were overhead (OH), ebb and flood (EF), and float (F). At 2 and 4 wk, banana and bell pepper injury was greatest from clomazone (1.1 kg/ha) treatments. Banana and bell pepper yield were not influenced by herbicide treatment. Although crop injury was greater in 1997, there was no herbicide or irrigation system interaction with year. OH and EF irrigated banana pepper and OH irrigated bell pepper produced the greatest total yield over two harvests, whereas F irrigated pepper yielded the least. F irrigated bell pepper plants had reduced early total yield and fancy fruits relative to other irrigation treatments. F irrigated plants yielded 32 and 22% less than OH irrigated plants in banana and bell pepper, respectively. Stand counts at 3 wk after planting (WAP) show that, unlike OH and EF treatments, F treatments lost 240 to 330 plants/ha. Differences in stand among treatments were greater in 1997 than 1996. Based on our study, the OH irrigated system appears to be the best system for producing bell pepper transplants with the greatest total yield. With banana pepper, both OH and EF irrigated systems appear to produce banana pepper transplants with the greatest total yield. Also, pepper transplant tolerance to herbicides is not affected by the irrigation system used to produce transplants.

Three experiments were conducted in the field using common cocklebur as a test species to identify weed growth differences due to propagation method and weed age when transplanted (with no crop and with soybean). Two experiments involved weed establishment in noncrop areas using four propagation methods (direct seeded–transplanted, peat tablets, peat pots, and plastic inserts) in a factorial arrangement with three transplant timings (at the cotyledon stage, at two true leaves, and at four true leaves). A direct-seeded method was also included as a check. Propagation methods and transplant timings were contrasted to the direct-seeded method because it was the “most natural” method of those tested. Based on results from the first year, the peat tablet method at the three transplant timings plus the direct-seeded method were used to establish the weed in a field experiment with soybean. In 1996 at 4 wk after emergence (WAE), 8 WAE, and senescence, weeds planted in peat tablets and transplanted at the cotyledon stage were most similar to the direct-seeded method. Peat pots and plastic inserts displayed an intermediate number of differences, whereas direct-seeded–transplanted weeds exhibited the most differences of any propagation method. Transplanting at the two-leaf stage showed more differences, with the four-leaf stage showing even more. In 1997 at 4 WAE, few propagation methods or transplant timings were different from the direct-seeded method. Results from harvests at 8 WAE and at senescence were comparable to those in the previous year. Differences between years at 4 WAE were attributed to greater heat stress and less moisture early in 1996. When common cocklebur was grown in soybean, no differences were detected at 4 WAE between peat tablets transplanted at the cotyledon stage vs. direct-seeded weeds and only one difference when transplanted at the two- and four-leaf stages. At 8 WAE, the early transplant was again the most comparable treatment to direct-seeded weeds, with many differences at the later transplant timings. At senescence, weed differences were no longer apparent. Patterns established for peat tablets with the weed growing alone largely held true when it was grown with soybean.

Suppression of grass encroachment of one warm-season grass into another species is an important management tool. Two field studies were conducted in Georgia to determine the timing, rates, and frequency of ethofumesate plus flurprimidol applications needed to suppress three bermudagrass cultivars and determine what effects these treatments have on tolerance of three seashore paspalum cultivars during 1998 and 1999. Tank-mixes of ethofumesate and flurprimidol applied at the 1× rate (1.7 + 0.8 kg/ha) on April 1 suppressed ‘TifEagle’ bermudagrass effectively (≥ 78%) by late September. However, the suppression of ‘Tifway’ bermudagrass (≤ 39%) and ‘common’ bermudagrass (≤ 67%) was not acceptable at the same rates and timing. Ethofumesate plus flurprimidol applied at the 1× rate in April severely injured all paspalum cultivars 61 to 65% within a 2- to 6-wk period, but the cultivars recovered to an acceptable level (≤ 30%) by 10 wk. In most instances, reduced ethofumesate plus flurprimidol rates (¼× and ½×) following the 1× rate in April did not injure the paspalum cultivars as severely as did the initial 1× rate. However, bermudagrass suppression was improved from the multiple treatments. When the chemicals were applied initially at the 1× rate and followed by four timely ¼× rates, bermudagrass suppression by late September was ≥ 72% for all bermudagrass cultivars, with the exception of common bermudagrass in 1998 (52%). Maximum injury to the paspalum cultivars during 1998 and 1999 from the four repeated ¼× rates ranged from 16 to 45% for ‘Sea Isle 1’, to 33 to 37% for ‘Sea Isle 2000’, and 21 to 52% for ‘K-3’. Ethofumesate plus flurprimidol applied initially at the 1× or 2× rate on June 30 and followed by a repeated application on July 25 did not effectively suppress (≤ 70%) common bermudagrass either year or Tifway bermudagrass in 1999. However, the suppression of common bermudagrass (≥ 83%) and Tifway bermudagrass (≥ 90%) was effective when the chemicals were applied initially at the 2× rate on June 30, followed by a 2× rate on July 25 and a 1× treatment on August 14. TifEagle bermudagrass was effectively suppressed (≥ 85%) when applied initially on June 30 and July 25 at the 1× rate. Ethofumesate plus flurprimidol applied once at the 1× rate on June 30 caused ≤ 46% injury to paspalum cultivars. The injury was generally ≥ 50% when the chemicals were applied in two or more applications.

Buried feral rye seeds were rapidly depleted in soil in the first year due to in situ germination. Less than 1% of the viable seeds persisted after 45 mo of burial. Although after 5 yr, a small number of seedlings still emerged, soil seedbank decline was rapid when seed production was prevented. A low level of induced dormancy was detected and may explain the small populations of feral rye that persisted. Seed and seedling population shifts were large over a 5-yr period and were related to environmental conditions. Tillage or chemical control of feral rye in the fallow period reduced populations compared to the untreated weedy check. Moldboard plowing provided the greatest feral rye control compared to shallow tillage and chemical fallow. Feral rye seedbank populations rebounded following a wet final year of the study. These results help explain feral rye persistence in a wheat–fallow agroecosystem by the persistence of a small portion of the seedbank and by large seed inputs into the system during environmentally favorable years. Feral rye reduced wheat yield as much as 92% and represented up to 73% contamination in harvested wheat.

Combinations of 0 to 1,120 g ae/ha 2,4-D plus 0 to 42 g ai/ha metsulfuron were evaluated in both field and greenhouse experiments. Addition of metsulfuron to 2,4-D increased Virginia buttonweed (Diodia virginiana) fresh weight reduction in the greenhouse compared with 2,4-D alone, but reduction in fresh weight was not different from 32 g/ha or more of metsulfuron applied alone. In field experiments 5 wk after treatment (WAT), combinations of metsulfuron and 2,4-D did not control Virginia buttonweed greater than 32 g/ha or more of metsulfuron alone. No synergism for the combinations was observed. Field experiments conducted from 1991 to 1993 evaluated three-way combinations of herbicides for Virginia buttonweed control. Treatments included: 2,4-D plus mecoprop plus dicamba (five herbicide premixes), 2,4-D plus dichlorprop plus dicamba, 2,4-D plus MCPA plus dichlorprop, mecoprop plus MCPA plus dichlorprop, or 2,4-D plus mecoprop plus dichlorprop. Combinations containing at least 688 g/ha 2,4-D provided the most consistent Virginia buttonweed control 2 WAT. By 7 WAT, control was no more than 60% for any treatment. A separate experiment evaluated the effects of repeated applications of two- or three-way herbicide mixtures applied at least 5 wk apart when ground cover regrowth was 25%. Treatments included: 2,4-D plus dichlorprop plus dicamba ester, 2,4-D plus mecoprop plus dicamba amine, 2,4-D plus dichlorprop amine, or 2,4-D plus dichlorprop ester. Ground cover 1 yr following application of sequential treatments was 35% or less compared to 65% in the nontreated control. Following 2 yr of herbicide application, ground cover in the treated plots was 28% or less.

Goosegrass control studies were conducted with multiple preemergence (PRE) and postemergence (POST) herbicides on bermudagrass fairways on the tropical island of Guam. Two POST applications of MSMA plus metribuzin, applied 1 wk apart were needed to control the existing goosegrass. Three applications of these herbicides showed a clear trend in goosegrass control, with control lasting 4 wk longer than two treatments. PRE herbicides provided efficacious control only when applied in sequence with a single MSMA plus metribuzin application. The control from sequential applications of PRE herbicides was generally no better than that with two applications of MSMA plus metribuzin. However, application of MSMA plus metribuzin resulted in turf discoloration lasting 5 to 8 wk. A single POST application reduced turf quality from 35 to 41% when compared to the untreated check. Two applications caused an additional 5 to 7% reduction in turf quality. Three applications caused similar discoloration as two applications. Application of PRE herbicides had no effect on turf quality, with ratings being equal to those of plots treated with POST herbicides only.

A field study evaluated the effects of green kyllinga establishment method (seed vs. stolon), two mowing heights (2.5 and 5.0 cm), and three nitrogen (N) rates (0, 24, and 49 kg/ha/mo) on green kyllinga infestation in ‘Tifway’ bermudagrass turf. The study was initiated in vigorous and newly established or “weak” bermudagrass turf in May 1997 and continued until December 1998. The green kyllinga area was measured periodically each year and plant dry weight (g/500 cm2) was calculated in December 1997 and 1998. In 1997, stolon established green kyllinga plots were twice as large as seeded plots in vigorous turf and four times larger in weak turf. Method of establishment, however, was less important in 1998 as seedling populations became more established. In weak turf, increasing N rate to 49 kg/ha/mo decreased green kyllinga spread by 50% in 1997 and by 40% in 1998 compared to no N. In vigorous turf, mowing height influenced green kyllinga infestation more than N. Low mowing height (2.5 cm) increased green kyllinga infestations nearly twofold in vigorous turf in 1997 and more than fivefold in 1998. Golf course fairways are often maintained at clipping heights shorter than 2.5 cm, and green kyllinga is a prevalent weed at these sites. Green kyllinga may gain a competitive advantage in bermudagrass turf at lower mowing heights.

Tropical soda apple (TSA) was evaluated for response to 28 herbicide treatments. Treatments containing picloram or triclopyr controlled eight-leaf, 16-leaf, and 1-yr-old TSA greater than 90% 8 wk after treatment (WAT). Control of 1-yr-old TSA did not increase 8 WAT when triclopyr was mixed in diesel fuel rather than water. In greenhouse additive interference experiments, populations of 0, 1, 2, 4, 8, 16, 32, and 64 TSA plants/700 cm2 of tall fescue had no effect on tall fescue height. TSA height was affected by TSA population, and intraspecific TSA competition was expressed as etiolation at densities greater than 4 plants/700 cm2. Averaged over five periods of competition, predicted yield losses of tall fescue were 14, 16, 29, and 31% and 1, 11, 19, and 23% for 8, 16, 32, and 64 TSA plants/700 cm2, respectively, for each experiment. Differences in tall fescue dry matter response between experiments were attributed to ambient temperature. Dry matter per individual TSA plant decreased from 1.7 to 0.3 g as TSA density increased from 1 to 64 plants/700 cm2. Percent canopy coverage of TSA relative to an area of 700-cm2 surface increased proportionally as tall fescue coverage decreased. After 10 wk of competition, TSA monopolized the canopy with coverage of 92 and 94%; tall fescue coverage was limited to only 7 and 5% in experiments I and II, respectively.

Experiments were conducted to determine whether antagonism between atrazine and glyphosate on shattercane observed in field studies could be duplicated under greenhouse conditions on ‘Rox Orange’ forage sorghum and whether it could be overcome by the addition of ammonium sulfate, other adjuvants, or additional glyphosate. Atrazine or surfactant added to glyphosate did not significantly affect sorghum dry weights compared to glyphosate alone. The Colby equation for synergism indicated that atrazine did not antagonize sorghum control with glyphosate in the greenhouse. Glyphosate at 0.43 kg ae/ha plus ammonium sulfate provided greater control of sorghum than glyphosate at 0.43 kg/ha without ammonium sulfate; however, glyphosate at 0.84 kg/ha plus ammonium sulfate did not provide greater control of sorghum than glyphosate at 0.84 kg/ha without ammonium sulfate. Reduced activity of glyphosate at 0.43 kg/ha in the absence of ammonium sulfate was likely due to an abundance of calcium cations in the carrier water that associated with glyphosate molecules and subsequently reduced herbicide uptake by plants. Thus, antagonism observed under cool conditions in field studies was not evident in controlled-temperature greenhouse studies.

A study was conducted at three locations in Saskatchewan, Canada, in 1996 and 1997 to determine if increasing the seeding rate of wheat, barley, and lentil by 50% would maintain weed control and crop yield when herbicides are applied at reduced rates or not at all. Three herbicide rates (½ of full, ¾ of full, and full recommended label rate), along with an untreated check, two crop seeding rates (normally recommended and 1.5 times normally recommended rates), and three crops were tested. Increasing seeding rate did not affect weed fresh weights, crop yield, and net return responses to herbicides applied at reduced rates or not at all when averaged across crops, years, and locations. Increased seeding rate, independent of the different herbicide applications, had infrequent and inconsistent effects among the crop by year by location combinations. More broadleaf and grass weed growth, less crop yield, and lower net returns generally occurred when herbicides were not applied or applied at reduced rates. These trends were especially prominent when herbicides were not applied to cereal crops at Saskatoon (40% yield reduction) and when herbicides were applied at ½ the full label rate rather than higher herbicide rates to wheat at the other two locations (16% yield reduction). In 1996, lentil yield and net returns did not respond to herbicide application and rate because of poor grass weed control across all herbicide rates. Lentil yield and net returns decreased by 11% (full vs. ¾), 22% (¾ vs. ½), and 46% (½ vs. none) when herbicides were applied at progressively lower rates in 1997. Reduced herbicide rates did not affect net returns for cereal crops, indicating that herbicide rates lower than the full label rate may be economically viable in certain crops.

Absorption and translocation of nicosulfuron and dicamba applied alone and combined was studied in 25-cm-high hemp dogbane originating from lateral roots that had overwintered. Absorption of 14C-nicosulfuron by hemp dogbane was not affected by applications of 70 g ai/ha unlabeled dicamba. Upward translocation of 14C-nicosulfuron in hemp dogbane was 86% greater 6 d after treatment (DAT) when dicamba was tank mixed with nicosulfuron, compared to nicosulfuron applied alone. Combinations of nicosulfuron plus dicamba increased translocation of nicosulfuron to hemp dogbane crown and roots 237 and 130%, 1 and 6 DAT, respectively, compared to nicosulfuron applied alone. Absorption of 14C-dicamba by hemp dogbane was not affected by the addition of 31 g ai/ha nicosulfuron. Upward translocation of dicamba in hemp dogbane was 42% greater 6 DAT for nicosulfuron plus dicamba compared to dicamba applied alone. Increased hemp dogbane control with nicosulfuron plus dicamba compared to either herbicide applied alone can be explained by enhanced translocation of both herbicides.

New weed management tools and growth regulators make production of ultra narrow row (UNR) cotton possible. Weed control, cotton yield, fiber quality, and net returns were compared in UNR bromoxynil-resistant, glyphosate-resistant, and nontransgenic cotton. Weeds included broadleaf signalgrass, carpetweed, common cocklebur, common lambsquarters, common ragweed, goosegrass, jimsonweed, large crabgrass, Palmer amaranth, pitted morningglory, prickly sida, sicklepod, smooth pigweed, and tall morningglory. Pendimethalin preplant incorporated (PPI) in conventional-tillage or preemergence (PRE) in no-till systems plus fluometuron PRE did not adequately control many of these weeds. Pyrithiobac plus MSMA early postemergence (POST) often was more effective than pyrithiobac alone. Pendimethalin plus fluometuron at planting followed by pyrithiobac plus MSMA early POST controlled sicklepod 82%, goosegrass 89%, Palmer amaranth 92%, and the other species at least 95% late season. Pyrithiobac at mid-POST did not improve control. Bromoxynil plus MSMA early POST was more effective than bromoxynil alone only on sicklepod. Pendimethalin plus fluometuron at planting followed by bromoxynil plus MSMA early POST controlled sicklepod 62%, Palmer amaranth 81%, goosegrass 83%, and all other species at least 95%. Glyphosate early POST did not adequately control many species due to sustained weed emergence. Glyphosate early POST followed by glyphosate late POST (after last effective bloom date) controlled all species except pitted morningglory and tall morningglory at least 93%. Pendimethalin plus fluometuron followed by glyphosate early POST was the most effective glyphosate system overall, and it controlled sicklepod 88%, pitted morningglory 90%, and other species at least 93%. Glyphosate late POST did not increase control in systems with pendimethalin plus fluometuron at planting followed by glyphosate early POST. Yields and net returns were similar with all herbicide/cultivar systems at two of five locations. At other locations, yields and net returns were similar with systems of pendimethalin plus fluometuron at planting followed by pyrithiobac plus MSMA early POST, pendimethalin plus fluometuron followed by bromoxynil plus MSMA early POST, and glyphosate early POST. Greatest yields and net returns were obtained with pendimethalin plus fluometuron at planting followed by glyphosate early POST. Herbicide systems did not affect fiber quality.

Seeds of giant foxtail (Setaria faberi, 4,000 seeds/m2) or velvetleaf (Abutilon theophrasti, 3,000 seeds/m2) were added to the seed bank to determine the effect of increases in weed density on herbicide efficacy in corn (Zea mays). A herbicide program consisting of SAN 582 applied preemergence followed by a postemergence application of dicamba plus atrazine was evaluated at four levels (0.0, 0.3, 0.7 and 1.0 times the label rates). At a site with low initial weed densities, the addition of velvetleaf or giant foxtail seed to the seed bank did not influence herbicide efficacy at the 1.0× rate at 9 wk after planting (WAP). Giant foxtail densities were greater 9 WAP in augmented areas than in the native seed bank plots at both the 0.3× and 0.7× rates, whereas with velvetleaf, higher densities in augmented plots were seen only at the 0.3× rate. In areas with high native weed densities, addition of seed of either species resulted in an increase in final weed densities at all herbicide rates.

Experiments compared the effect on weed control and potato yield of banded applications of metolachlor plus linuron with or without flex-tine, rolling, and shovel cultivation prior to hilling. Cultivation without banded herbicide resulted in greater prehilling in- and between-row weed densities and reduced late-season weed control as compared to broadcast herbicides or cultivation with banded herbicides. Although the flex-tine and rolling cultivators were expected to provide improved in-row weed control, there were few differences between these and the other cultivation implements. Despite reduced weed control with cultivation alone, potato yields were not reduced.

Kochia (Kochia scoparia) control dropped from about 90% to less than 20% after three consecutive annual applications of acetolactate synthase (ALS)-inhibiting herbicides in several northeastern South Dakota fields. Field experiments were conducted to evaluate control of kochia resistant to ALS-inhibiting herbicides using combinations of herbicides applied postemergence (POST) in wheat (Triticum aestivum) and using herbicides applied preemergence (PRE), POST, and PRE plus POST in soybean (Glycine max). Thifensulfuron plus tribenuron did not control kochia in wheat (> 600 kochia plants/m2 at harvest) and wheat yield was similar to yield of the untreated control. Dicamba plus 2,4-D (in 1996) and bromoxynil plus MCPA (in 1996 and 1997) controlled kochia and increased yields by 15% or more. Kochia was sparse (less than 1 plant/m2) in soybean plots, but grass weeds were prevalent. PRE plus POST or POST herbicide combinations that included ALS-inhibiting herbicides controlled grasses, and soybean yields were as much as 20% greater than yields with combinations that did not contain ALS-inhibiting herbicides. Adding ALS-inhibiting herbicides to wheat herbicide combinations decreased profitability because treatment costs increased while yields did not. In contrast, adding ALS-inhibiting herbicides to soybean treatments increased profitability due to better grass control, resulting in increased yield and better return.

Glyphosate is often mixed with residual herbicides to control emerged weeds in no-till crop production systems. Field studies were conducted in Ohio from 1992 to 1994 to evaluate the weed control provided by residual herbicides and reduced rates of glyphosate in full-season, no-till soybean. Herbicide treatments were applied at two timings to examine the effect of weed size. At 4 wk after treatment, greater than 85% Pennsylvania smartweed control was obtained with metribuzin plus chlorimuron and linuron plus chlorimuron applied with 280 g ai/ha glyphosate and with imazethapyr and imazaquin applied with 560 g/ha glyphosate. All residual herbicides provided at least 85% common lambsquarters control when applied with 560 g/ha glyphosate. In 1992, the early application of residual herbicides provided this level of common lambsquarters control without glyphosate due to the small weed size at the time of application. Residual herbicides applied with 280 g/ha glyphosate controlled giant foxtail 85% or greater. Higher glyphosate rates were needed to control barnyardgrass. The performance of reduced glyphosate rates was dependent on weed species and weed size.

Laboratory studies were conducted to determine if electrolyte leakage from either leaf tissue, germinating seeds, or excised roots correlated with previously established soil-applied field response of soybean cultivars and target weeds to sulfentrazone. Sulfentrazone-induced electrolyte leakage from leaf tissue of coffee senna (sensitive), sicklepod (tolerant), and soybean cultivars ‘Asgrow 6785’ and ‘Carver’ (sensitive) and ‘Stonewall’ and ‘DPL 3606’ (tolerant) was monitored over time. Electrolyte leakage from leaf tissues, caused by 25 ppm (65 μM) sulfentrazone, agreed directly with the known response of these weeds, but response of the four soybean cultivars was equivalent. Furthermore, sulfentrazone-induced electrolyte leakage from leaf tissue of Asgrow 6785 and Stonewall was not affected by sulfentrazone concentration as high as 100 ppm (258 μM) nor by light intensity (4 and 120 μmol/m2/s photosynthetically active radiation). For germinating seeds, sulfentrazone-induced electrolyte leakage was also independent of soybean cultivar. In contrast, electrolyte leakage from excised roots of germinal soybean seedlings did concur directly with the previously established cultivar sensitivity to soil-applied sulfentrazone. Results indicate that electrolyte leakage from excised roots of soybean germinal seedlings can be used to assess cultivar sensitivity to soil-applied sulfentrazone.