Greenhouse studies were conducted to determine the responses of ripgut brome and foxtail brome to MON 37500 applied at rates up to 80 g/ha. At 30 d after treatment MON 37500 at 20 g/ha reduced fresh weight of ripgut brome by 89% when applied at the three-leaf stage and 57% when applied at the tillering stage. MON 37500 at 10 g/ha reduced fresh weight of foxtail brome by 80% when applied at the three-leaf stage and 61% when applied at the tillering stage. Rates above 20 g/ha did not increase control of either species. In field experiments during 1998 to 1999 and 1999 to 2000 in Settat, Morocco, bread wheat tolerated MON 37500 at 67 g/ha. Ripgut brome control in the field was 78% in the first growing season and 90% in the second season when MON 37500 was applied at 27 g/ha to brome plants at the one- to four-leaf stage. A similar rate controlled tillering ripgut brome by 69% during 1998 to 1999 and 62% during 1999 to 2000. MON 37500 at 20 to 30 and 10 to 20 g/ha applied before tillering controlled ripgut brome and foxtail brome, respectively, ≥ 70%.

Field experiments were conducted from 1997 to 1999 at Ejea and at Valdegon (Spain) to study weed control and tolerance of direct-seeded pepper ‘Agridulce SIA’ to clomazone alone or with linuron, napropamide, or pendimethalin. The main weeds at Ejea were redroot pigweed, Diplotaxis erucoides, common purslane, and ivyleaf speedwell, while at Valdegon they were Solanum physalifolium and common purslane. Pepper was tolerant to clomazone applied at 0.18 kg ai/ha, but weed control was less than 77%. Increasing the rate of clomazone to 0.36 kg/ha controlled weeds at least 85% and did not injure pepper. Clomazone at 0.54 and 0.72 kg/ha injured pepper 6 wk after planting (WAP), but plants recovered and the dry weight and yield of paprika were not affected. Napropamide at 2.03 kg ai/ha applied with clomazone improved the control of D. erucoides. Addition of pendimethalin at 0.17 to 0.25 kg ai/ha to clomazone did not improve weed control and increased pepper injury 6 WAP in 1 of 2 yr, but yield was not affected. Linuron at rates ranging from 0.08 to 0.13 kg ai/ha used in combination with clomazone provided complete weed control but injured pepper the most (34 to 88%) and reduced pepper stand by 50% in 1 yr.

A 3-yr study was conducted to assess cranberry bean susceptibility to mechanical weeding using a rotary hoe at preemergence, hook, cotyledon, unifoliate, and first to fourth trifoliate stages of bean development and at different combinations of stages. The experiment was conducted in a weed-free environment. Cultivation with the rotary hoe reduced bean yield only for the treatment that received four cultivations at four different bean growth stages. Three cultivations improved yield compared with no cultivation. Single cultivation done at any of the eight crop growth stages did not affect yield. Crop density at harvest was decreased 6% in the treatments receiving two cultivations and 9% in the treatments receiving four cultivations compared to no cultivation. The effects of the cultivations on grain moisture were not consistent and differed from year to year. Seed weight did not differ among treatments in either year. Because this study was conducted under weed-free conditions, the beneficial effects of cultivating with the rotary hoe are probably mostly related to breaking the soil crust, improving soil aeration, preserving soil moisture, or promoting mineralization of the nutrients required by the crop.

Field experiments were conducted in 1996 and 1997 to evaluate weed control and dry bean response to mechanical tillage and herbicide treatments. Herbicide treatments were EPTC plus ethalfluralin, dimethenamid, and imazethapyr plus bentazon. Herbicides were applied alone or combined with rotary hoeing and in-row cultivation. Differences in dry bean yields between years were due to differences in weed density. Weed species included redroot pigweed, common lambsquarters, hairy nightshade, wild proso millet, and green foxtail. Weed density in the untreated check plots at the end of the growing season was 35 plants/m2 in 1996 and 134 plants/m2 in 1997. Dry bean stands were not reduced by rotary hoeing, in-row cultivation, and herbicides in 1996, but in-row cultivation reduced dry bean populations 27% compared to the hand-weeded check in 1997. In-row cultivation and rotary hoeing provided similar weed control in both years. At low weed densities, either mechanical tillage or herbicides alone were effective in suppressing weeds, whereas at higher densities, herbicides combined with mechanical tillage were required for effective control.

An experiment was conducted in 1998 and 1999 in southeastern Pennsylvania to examine the effect of tillage and soybean row spacing on burcucumber emergence and growth. A second experiment evaluated postemergence (POST) soybean herbicides on burcucumber control. In the tillage and row spacing study, a glyphosate-resistant soybean variety was planted in no-till and reduced-tillage systems in 38- and 76-cm row spacings. In the POST herbicide experiment, chlorimuron, glyphosate, CGA-277476, thifensulfuron, and several combinations of these herbicides were applied at two different POST application timings in 38-cm row soybean planted in a reduced-tillage system. In the tillage and row spacing study, burcucumber emergence was greatest starting in late May through mid-June and mostly ceased by early July, regardless of tillage system or row spacing. Although there was no difference in germination period in either tillage system, preplant tillage increased the number of emerged plants by 110% in 1997 and 70% in 1998 compared to the no-till system. Row spacing had no effect on burcucumber emergence or biomass production. In general, most POST herbicide programs controlled burcucumber, and there was no difference between early POST and mid-POST application timings. Chlorimuron at 13 g ai/ha, chlorimuron plus thifensulfuron, glyphosate, glyphosate plus chlorimuron, and glyphosate plus CGA-277476 provided 87% or greater control of burcucumber 12 wk after planting. These herbicides reduced burcucumber density and biomass by more than 56% in 1997 and 96% in 1998.

Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec, Canada, and in 1996 at Ottawa, Ontario, Canada, to quantify the impact of corn hybrids, differing in canopy architecture and plant spacing (plant population density and row spacing), on biomass production by transplanted and naturally occurring weeds. The treatments consisted of a factorial combination of corn type (leafy reduced stature [LRS], late-maturing big leaf [LMBL], a conventional Pioneer 3979 [P3979], and, as a control, a corn-free condition [weed monoculture]), two weed levels (low density [transplanted weeds: common lambsquarters and redroot pigweed] and high density [weedy: plots with naturally occurring weeds]), two corn population densities (normal and high), and row spacings (38 and 76 cm). At all site-years under both weed levels, the decrease in biomass production by both transplanted and naturally occurring weeds was greater due to the narrow row spacing than due to the high plant population density. The combination of narrower rows and higher population densities increased corn canopy light interception by 3 to 5%. Biomass produced by both transplanted and naturally occurring weeds was five to eight times less under the corn canopy than in the weed monoculture treatment. Generally, weed biomass production was reduced more by early-maturing hybrids (LRS and P3979) than by LMBL. Thus, hybrid selection and plant spacing could be used as important components of integrated pest management (weed control) for sustainable agriculture.

The potential of Colletotrichum dematium f.sp. epilobii (ATCC 20981) to control fireweed (Epilobium angustifolium) was investigated. Under controlled environment conditions, plant age, inoculum density, length of the dew period, and temperature during the dew period affected the efficacy of C. dematium f.sp. epilobii. Seedlings sprayed with 1 × 109 conidia/m2 sustained the most damage. Susceptibility decreased with increasing plant age, and 10-wk-old plants were slightly affected by the fungus. Satisfactory levels of control were achieved when the dew period was >20 h and temperature during the dew period was 30 C. Control of fireweed increased when the C. dematium f.sp. epilobii conidia were suspended in a 25% v/v canola oil/water emulsion. Using this formulation, control of 4-wk-old seedlings was obtained with a 10-fold reduction in inoculum concentration (1 × 108 conidia/m2), the required dew period was reduced to 12 h, and the effect of the temperature during the dew period was minimized. In the field, C. dematium f.sp. epilobii alone or when amended with an oil emulsion failed to control fireweed growth. When the oil formulation of C. dematium f.sp. epilobii was tank mixed with a low rate of glyphosate, high levels of control were consistently achieved. Growth reduction achieved with this formulation was more than additive, suggesting a synergistic interaction. The effectiveness of the formulated conidial suspension of C. dematium f.sp. epilobii decreased with plant maturity, and 15-wk-old plants were not controlled. C. dematium f.sp. epilobii alone has limited potential as a candidate bioherbicide, but when formulated in an oil/water emulsion and combined with low rates of glyphosate, suppression of fireweed can be attained in the field.

The efficacy of preemergence (PRE) applications of ethalfluralin or pendimethalin incorporated with irrigation was compared with mechanical preplant incorporated (PPI) applications at equivalent rates in peanut. PRE applications of herbicides followed by irrigation were as effective as PPI applications in controlling Texas panicum, southern crabgrass, and crowfootgrass. Split PPI/PRE applications of ethalfluralin were more effective than PPI applications in controlling Texas panicum in 2 of 3 yr. Sequential postemergence applications of clethodim or sethoxydim increased the control of Texas panicum when ethalfluralin or pendimethalin controlled Texas panicum less than 82%. No differences in peanut yield were observed between PPI or PRE applications of either ethalfluralin or pendimethalin.

Field experiments were conducted in 1997 and 1998 at the Prattville Experiment Field in Prattville, AL and the Wiregrass Substation in Headland, AL to determine if ammonium thiosulfate (ATS) additions to monosodium methanearsonate (MSMA) affects weed control, reduces MSMA-induced cotton injury, lessens the fruiting and maturity delay on cotton caused by MSMA, and lessens MSMA-induced yield reductions in cotton. Treatments were applied before cotton was at the pinhead square stage and the weeds were 5 cm tall. Weeds evaluated were sicklepod, morningglory species, yellow nutsedge, and Texas panicum. ATS additions to MSMA occasionally enhanced control of all weeds 5 to 20%. However, the addition of ATS did not reduce crop injury caused by MSMA, the effects of MSMA on cotton maturity, or yield reductions caused by MSMA.

Field studies were conducted near Painter, VA, in 1995 and 1996 to investigate the effects of herbicides and cultivation on weed control, yield, and net returns in potato. Potato injury from herbicides and/or cultivation was not observed in 1995 and was less than 12% in 1996. Metribuzin plus metolachlor preemergence controlled yellow nutsedge by at least 81% regardless of the number of cultivations in 1995 and 1996. Yellow nutsedge control with metribuzin plus rimsulfuron postemergence (POST) plus three cultivations was as high as 70% in 1995 and 88% in 1996. Metribuzin plus rimsulfuron POST controlled common lambsquarters by at least 95% and common ragweed by at least 83% regardless of the number of cultivations in 1995 and 1996. A-size tuber production and net returns from potato receiving herbicides were not improved with two or three cultivations in 1995 or 1996. However, when averaged over all weed control systems (herbicide and cultivation-only systems) multiple cultivations significantly increased control of all weed species, A-size tuber production, and net returns.

Sulfonylurea herbicide residues in soil can affect rotational crops even at low concentrations. Although analytical methods are efficient enough to measure them, the lack of an efficient herbicide extraction technique makes bioassays useful for determining the presence of phytotoxic levels of sulfonylurea residues in soil. A growth chamber bioassay using sunflower was developed to detect MON-37500 and triasulfuron residues in two different soils. Root length was measured 15 d after the treatment. A sigmoid equation described plant root length response as a function of herbicide concentration. The nonlinear regression established a range of I50 values from 0.9 to 2.9 ppb ai for both sulfonylureas.

MON 37500 was registered in 1999 for weed control in wheat and has the potential to injure following crops. Therefore, growth chamber experiments were conducted to determine the effect of soil properties on the phytotoxicity of MON 37500 residues, the relative tolerance of several potential rotational crops, and the joint effect of MON 37500 residues plus other herbicide residues on a susceptible crop. In 13 Alberta soils, the concentrations of MON 37500 and triasulfuron that reduced canola and barley dry matter by 50% (GR50) were correlated with soil organic matter (OM) and pH. The relationship that best described the effect of soil organic matter on GR50 for each herbicide–crop combination was GR50 = a + b(OM)2. There was no significant improvement in r 2 when pH and clay content were included in the equation. For soils with 2 and 10% OM content, predicted GR50 values for canola in MON 37500–treated soil are 2 and 26 ηg/g soil, respectively. Little injury to following canola is predicted in soils with OM contents > 4.5%. At similar concentrations, following crops such as canola, flax, lentil, and oriental mustard are predicted to be injured less by MON 37500 than by triasulfuron. The effect of combined residues of MON 37500 with triasulfuron, imazethapyr, or metsulfuron should be additive.

A random survey of 264 cropping fields in the Western Australian wheat belt was conducted to determine the extent of rigid ryegrass resistance to commonly used acetolactate synthase- and acetyl-CoA carboxylase-inhibiting herbicides. Rigid ryegrass infestation density was assessed and seed samples collected and subsequently tested for resistance to diclofop-methyl, clethodim, chlorsulfuron, and sulfometuron. Of these randomly collected populations, 46% exhibited resistance to diclofop-methyl and 64% to chlorsulfuron, with 37% exhibiting multiple resistance to both herbicides. Only 28% of tested populations were classified as susceptible to both diclofop-methyl and chlorsulfuron, although all but one population were susceptible to clethodim. Large differences in the proportion of fields containing resistant populations were found between agronomic areas, reflecting different cropping and, therefore, herbicide use history. There was no significant association between resistance status and the density at which rigid ryegrass was present. Herbicide-resistant rigid ryegrass populations are now more common than susceptible populations across much of the Western Australian wheat belt.

MKH 6562 is a new acetolactate synthase inhibitor herbicide that would provide an alternative to control wild oat. Three experiments were conducted at Scott, SK, Canada, from 1996 to 1999 to evaluate MKH 6562 rates (20 and 30 g ai/ha), carrier volumes (30, 50, and 100 L/ha), time of applications (two- to three-leaf and three- to four-leaf stages of wild oat), and broadleaf weed herbicide tank mixtures. Reduced wild oat control (lower visual rating of percent control and higher fresh weight) often occurred when MKH 6562 was applied at a rate of 20 vs. 30 g/ha, with carrier volumes of 30 vs. 50 and 100 L/ha, and at the three- to four-leaf vs. two- to three-leaf stages of wild oat. Wild oat control generally was lower for MKH 6562 tank mixed with dicamba + mecoprop + MCPA 1:1:4.4 and bromoxynil + MCPA 1:1 compared with MKH 6562 applied alone or tank mixed with other broadleaf herbicides. MKH 6562 tank mixed with MCPA, and to a lesser extent 2,4-D, resulted in decreased wild oat control when applied at the three- to four-leaf stage of wild oat, but not at the two- to three-leaf stage. Wheat grain yield usually was not affected by MKH 6562 rate and carrier volume. Yield was 7% lower when MKH 6562 was tank mixed with dicamba + mecoprop + MCPA or fluroxypyr + 2,4-D and was 8% lower when MKH 6562 was applied in a mixture with 2,4-D formulations or bromoxynil + MCPA at the three- to four-leaf stage compared with the two- to three-leaf stage. Similar yields were achieved when MKH 6562 was applied alone at both leaf stages of wild oat. Wild oat control and wheat yield with MKH 6562 were as good as or better than with ICIA 0604 and imazamethabenz and were as good as or poorer than with CGA 184927. MKH 6562 provides adequate control of wild oat in wheat when applied early with the recommended carrier volume. Satisfactory control may be achieved with reduced rates if wild oat infestations are light.

Herbicide efficacy, coverage, and retention were evaluated for spray applied through Drift Guard, Turbo TeeJet, AI TeeJet, and TurboDrop drift-reducing nozzles compared to a conventional flat-fan nozzle. Percentage spray coverage detected on water-sensitive cards was greater for conventional and Drift Guard nozzles than for Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. Spray without adjuvants was retained better by redroot pigweed for treatments applied with conventional and Drift Guard nozzles than Turbo TeeJet, AI TeeJet, and TurboDrop nozzles. However, spray with adjuvants was retained similarly for all nozzle types when averaged over spray adjuvant and two weed species. The efficiency of spray retention was greater for spray applied in 47 than in 190 L/ha spray volume for all nozzles. Paraquat and glyphosate, representing contact and translocated herbicides, respectively, provided similar grass species control for all nozzle types, regardless of spray volume. Paraquat and glyphosate were also equally or more effective in 47 compared to 190 L/ha spray volume.

A 2-yr field study was conducted during 1998 and 1999 at Stoneville, MS, on a Dundee silt loam to determine weed control, yield, and net return associated with winter cover crops in soybean. Cover crop systems included Italian ryegrass, oat, rye, wheat, hairy vetch, crimson clover, subterranean clover, no-cover crop conventional tillage (CT), and no-cover crop no-tillage (NT), all with standard preemergence (PRE), postemergence (POST), PRE + POST, and no-herbicide weed management. Oat (11.1 Mg/ha) had highest dry biomass compared to all other cover crops (6.0 to 7.6 Mg/ha) at soybean planting. Biomass decreased 9 wk after planting (WAP) compared to the respective biomass at soybean planting in all cover crops. Italian ryegrass and rye biomass decay was slow and about two-thirds of plant residue persisted at 9 WAP. Cover crops had no effect on densities of barnyardgrass, prickly sida, and yellow nutsedge, but altered the density of browntop millet. Total weed biomass was higher in rye, wheat, and subterranean clover than in Italian ryegrass cover crop systems, and higher with the PRE-only vs. POST-only or PRE + POST programs at 10 WAP soybean. Soybean yield decreased in the order of no-cover crop NT ≥ no-cover crop CT ≥ hairy vetch ≥ crimson clover ≥ rye ≥ oat ≥ wheat ≥ subterranean clover > Italian ryegrass. None of the cover crop systems gave soybean yield higher than the no-cover crop CT system in the absence of herbicides. Under a PRE-only program, all cover crop systems had lower yield compared to the no-cover crop CT system. When late-emerged weeds were controlled with POST applications (POST-only or PRE + POST programs), all cover crops, except Italian ryegrass, had no detrimental effect on soybean yields, which were not different from no-cover crop CT plots. In cover crops, input costs were high due to additional cost of seeds, planting, and desiccation. Net return was highest in no-cover crop NT ($105/ha) followed by no-cover crop CT ($76/ha) system. Net returns were negative for all cover crops and losses were highest in crimson clover (−$62/ha) and subterranean clover (−$161/ha).

Glyphosate effectively controls most weeds in glyphosate-resistant soybean. However, it is sometimes only marginally effective on Ipomoea spp. A field experiment was conducted at five locations in North Carolina to determine the effects of mixing 2,4-DB with glyphosate on Ipomoea spp. control and on soybean injury and yield. The isopropylamine salt of glyphosate at 560, 840, and 1,120 g ai/ha controlled mixtures of tall morningglory, entireleaf morningglory, and red morningglory at least 96% at two locations. Mixing the dimethylamine salt of 2,4-DB at 35 g ae/ha with glyphosate did not increase control but reduced soybean yield 6%. At two other locations, 2,4-DB increased control of tall morningglory and a mixture of entireleaf morningglory and ivyleaf morningglory 13 to 22% when mixed with glyphosate at 560 g/ha, but not when mixed with glyphosate at 840 or 1,120 g/ha. Soybean yield was reduced 31% at one location and was unaffected at the other. At the fifth location, 2,4-DB increased control of tall morningglory 25, 11, and 7% when mixed with glyphosate at 560, 840, and 1,120 g/ha, respectively. Soybean yield was increased 15%. In separate field experiments, glyphosate at 560, 840, and 1,120 g/ha controlled large crabgrass at least 99%. Mixing 2,4-DB at 35 g/ha with glyphosate did not affect control. In the greenhouse, mixing 2,4-DB at 35, 70, 140, or 280 g/ha with glyphosate at 70 to 560 g/ha did not affect large crabgrass control by glyphosate.

Research was conducted to compare the results of an enzyme-linked immunosorbent assay (ELISA) to high-performance liquid chromatography (HPLC) for detecting fluometuron in the environment. A linear relationship for HPLC (R2 > 0.90) and ELISA (R2 > 0.66) analysis was observed between the natural logarithm of the detected fluometuron concentrations regressed against time in soil collected from a cropped area, a grass filter strip, and a riparian forest. Both methods detected the same initial fluometuron concentration (y-intercept) for two of the three soils evaluated. The ELISA and HPLC measurements of fluometuron concentrations compared favorably with r values from 0.83 to 0.98. Predicted fluometuron half-lives determined from HPLC and ELISA measurements were: 110 and 112 d in the cropped watershed, 28 and 29 d in the riparian area, and 11 and 11 d in the grass filter strip, respectively. Results from both techniques indicated shorter half-lives in soil from the grass filter strip and riparian area than in cropped area soil. There was an inverse correlation between predicted half-lives and soil organic matter, pH, clay, and cation exchange capacity.

The premix atrazine + S-metolachlor is commonly used to control a wide range of weeds in corn, but it is weak on velvetleaf and several other broadleaf species. RPA 201772, used at reduced rates in combination with atrazine + S-metolachlor, may improve the weed control spectrum. In field studies at Urbana and Dekalb in 1998 and 1999, RPA 201772 was combined with a premix of atrazine at 1,820 g ai/ha and S-metolachlor at 1,408 g ai/ha to compare RPA 201772 rate effects on corn injury, weed control, and yield. RPA 201772 was applied at 0, 26, 53, 78, 105, and 132 g ai/ha early preplant (EPP), preplant incorporated (PPI), and preemergence (PRE). Compared with atrazine + S-metolachlor alone, RPA 201772 combinations did not improve giant foxtail control. However, RPA 201772 at 26 or 53 g/ha increased control of redroot pigweed, common lambsquarters, ivyleaf morningglory, common ragweed, giant ragweed, and velvetleaf in some environments. At Urbana in both years, RPA 201772 at 26 g/ha in combination with atrazine + S-metolachlor increased velvetleaf control 15% compared with the premix alone. RPA 201722 at 26 to 78 g/ha decreased velvetleaf densities with all application methods. Greater weed control and higher corn yield occurred in treatments applied PRE or PPI compared with EPP applications, except where conditions were dry after PRE applications. This research demonstrates the benefit of RPA 201772 at low rates for broadleaf weed control with less potential for crop injury compared with high RPA 201772 rates.

Volunteer potato plants are difficult to control in rotational crops, and they harbor harmful diseases, nematodes, and insects. Five herbicide treatments were evaluated for control of volunteer potato in field corn grown under no-till and conventional tillage in 1994 and 1995. In mid-June, potato control was greater in conventionally tilled corn than no-till corn primarily due to the reservoir tillage that followed postemergence (POST) herbicide applications in the conventional system. Final potato tuber weight was not different between tillage levels in 1994 or 1995. Herbicide treatments reduced potato tuber weight 64 to 96% in no-till corn and 85 to 99% in conventionally tilled corn compared to nontreated checks. Atrazine applied preemergence at 1.1 kg ai/ha followed by dicamba plus 2,4-D applied POST at 0.28 plus 1.1 kg ae/ha, respectively, reduced potato tuber weight greater than 95% in both years and both tillage systems. Corn yield was not affected by tillage level or herbicide treatments in 1994 or 1995 and averaged 10.5 MT/ha in 1994 and 15.1 MT/ha in 1995. In a separate experiment, glyphosate, dicamba plus 2,4-D, or fluroxypyr applied at the eight-leaf stage to potato grown without a corn crop, and followed by cultivation 10 d later, reduced the number of potato tubers produced 79 to 95% compared to nontreated potato.