Broadleaf weed control with postemergence applications of CGA-248757 and flumiclorac applied alone and in tank mixtures was evaluated in greenhouse and field studies. In greenhouse studies velvetleaf, common lambsquarters, redroot pigweed, common ragweed, common cocklebur, eastern black nightshade, and wild mustard shoot weight were reduced by 50% from 0.1, 2.9, 0.9, 1.1, 0.8, 0.4, and 1.2 g/ha of CGA-248757 and 0.7, 3.0, 2.4, 3.3, 3.0, 3.4, and 74.1 g/ha of flumiclorac, respectively. Under greenhouse conditions, tank mixtures of CGA-248757 or flumiclorac with atrazine, bentazon, bromoxynil, dicamba, halosulfuron, imazethapyr, lactofen, primisulfuron plus prosulfuron, or 2,4-D increased velvetleaf, common lambsquarters, redroot pigweed, or common ragweed control 14 d after treatment (DAT) when compared with the control provided by atrazine, bentazon, bromoxynil, dicamba, halosulfuron, imazethapyr, lactofen, primisulfuron plus prosulfuron, or 2,4-D applied alone. In field studies, adding CGA-248757 or flumiclorac to atrazine, bentazon, bromoxynil, dicamba, halosulfuron, imazethapyr, lactofen, CGA-277476, primisulfuron plus prosulfuron, or 2,4-D increased crop injury 3 DAT, but there was no reduction in corn or soybean yields as a result. In corn, tank mixtures of CGA-248757 or flumiclorac plus atrazine, dicamba, or 2,4-D increased velvetleaf control compared with treatments without CGA-248757 or flumiclorac. Tank mixtures of CGA-248757 or flumiclorac with primisulfuron plus prosulfuron increased common lambsquarters control compared with primisulfuron plus prosulfuron alone. Similarly, in soybean CGA-248757 or flumiclorac tank mixtures with bentazon or CGA-277476 increased control of redroot pigweed, and tank mixtures with lactofen increased common lambsquarters control. However, season-long broadleaf control in soybean with bentazon, lactofen, and CGA-277476 tank mixtures with CGA-248757 or flumiclorac did not provide acceptable weed control. Compared with imazethapyr alone the addition of CGA-248757 and flumiclorac improved soybean yield and provided season-long eastern black nightshade, common lambsquarters, redroot pigweed, and common ragweed control.

A full-season field study was conducted near College Station, TX to determine the competitive interference of Palmer amaranth on cotton development, yield, and fiber properties and to measure Palmer amaranth development as influenced by intraspecific competition. Palmer amaranth densities ranged from 0 to 10 plants/9.1 m of row. Palmer amaranth decreased cotton canopy volume by 45% at 10 wk after cotton emergence (WAE) and cotton biomass by greater than 50% at 8 WAE at the highest density. Cotton yields decreased linearly from 13 to 54% for 1 to 10 Palmer amaranth plants/9.1 m of row. Cotton lint properties were not influenced by Palmer amaranth density. Palmer amaranth volume and individual biomass were not affected by intraspecific competition at any of the densities.

Management of corn (Zea mays) row spacings and populations has been used for many years to increase corn productivity. In 1998 and 1999, nonirrigated corn was grown in 38-, 56-, and 76-cm row spacings at populations averaging 59,300, 72,900, and 83,900 plants/ha in Michigan. Glufosinate at 0.29 kg/ha was applied to common lambsquarters (Chenopodium album L.) averaging 5 cm in height in each plot. Corn population and row spacing did not influence weed emergence following application of glufosinate. Common lambsquarters biomass and seed production were reduced when grown under canopies of corn planted in populations exceeding 72,900 plants/ha. Common lambsquarters biomass was reduced as corn row spacings were reduced from 76 to 38 cm. Early-season interception of photosynthetic active radiation (PAR) by corn canopies increased as row spacings decreased, but differences were not apparent later in the season. Interception of PAR was similar throughout the season when corn populations exceeded 72,900 plants/ha. Corn yields were not affected by row spacing, but they were increased with corn populations of 72,900 plants/ha or higher.

Field studies were conducted near Archer, FL, and Vienna, GA, in 1995 and 1996 to investigate the effects of pyridate formulation and adjuvants on broadleaf weed control in peanut (Arachis hypogaea). Pyridate formulations SAN 319H 450EC 361LZ, SAN 319H 450EC 216LZ, and SAN 319H 600EC 418LZ were evaluated at two rates, 1.07 and 2.14 kg/ha. Pyridate at 1.07 kg/ha plus 2,4-DB at 0.23 kg/ha were evaluated alone and with five adjuvants. The adjuvants included a crop oil concentrate, a nonionic surfactant, a nonionic surfactant with organosilicone blend, urea ammonium nitrate plus a nonionic surfactant, and chlorothalonil (a fungicide) plus a nonionic surfactant. No pyridate treatment injured peanut. Pyridate formulation did not affect broadleaf weed control. Increasing pyridate rate increased weed control and yield. Mixing 2,4-DB with pyridate generally enhanced sicklepod (Senna obtusifolia) and common cocklebur (Xanthium strumarium) control. Florida beggarweed (Desmodium tortuosum), smallflower morningglory (Jacquemontia tamnifolia), hairy indigo (Indigofera hirsuta), sicklepod, and common cocklebur control with pyridate was not enhanced by adjuvants. Adding chlorothalonil to pyridate plus 2,4-DB did not affect weed control or peanut injury.

Field experiments were conducted during 1998, 1999, and 2000 in Santa Fe, Argentina, to evaluate chlorimuron, clethodim, flumetsulam, 2,4-DB, glyphosate, and haloxyfop for control of broadleaf and grass weeds in established alfalfa. Herbicides were applied to alfalfa, 6 to 10 cm in height, after first or second cuttings. Clethodim and haloxyfop were highly effective against bermudagrass, barnyardgrass, and knotroot foxtail, and alfalfa yields were increased. 2,4-DB was effective against Scotch thistle, swinecress, turnipweed, and birdsrape mustard, but no effects were observed on alfalfa yields. Chlorimuron, flumetsulam, and glyphosate were effective against burning nettle, common chickweed, common lambsquarters, spiny cocklebur, and Persian speedwell, but they injured alfalfa and decreased yields.

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.

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.

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.

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.

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.

Field trials were conducted in 1998 and 1999 to determine the effect of delayed burndown timings on weed control and yield of no-tillage glyphosate-resistant corn planted into soybean residue and into a wheat cover crop. Burndown treatments containing glyphosate were applied to both trials when the corn was planted (PRE), when the corn began to emerge (SPIKE), or when the corn had three visible leaves (3-LEAF). As burndown timing was delayed, velvetleaf control increased in corn planted into soybean residue. Glyphosate applied at 0.84 kg ae/ha at the SPIKE or 3-LEAF timing followed by a sequential application of glyphosate at 0.84 kg/ha controlled velvetleaf 91% and corn yields were similar to the weed-free plots. Corn yields among the burndown treatments were directly related to velvetleaf control. In the wheat cover crop trial, wheat treated at the PRE timing was completely controlled and corn yields were similar to the weed-free plots. As burndown timings were delayed, corn emergence and yields were severely reduced. Glyphosate applied at 0.84 kg/ha to 25-cm-wide strips over the corn row at planting and followed with delayed burndown timings increased corn emergence and yield.

Greenhouse and field experiments were conducted in North Dakota to determine the effect of adjuvants applied with imazapic on the control of leafy spurge and production of various grass species and to determine the most effective fall-application timing of imazapic for optimum leafy spurge control with minimal effect on herbage. Imazapic applied with a methylated seed oil (MSO) adjuvant tended to provide greater leafy spurge control than when applied with other types of adjuvants. Imazapic applied alone or with adjuvants reduced production of some grass species in the greenhouse, but it did not decrease herbage production in the field. Imazapic at 140 g/ha applied with MSO or with 28% N plus MSO averaged 72% leafy spurge control 12 mo after treatment, compared to 33% control from imazapic alone and 40% control from picloram plus 2,4-D. Imazapic at 140 g/ha applied with MSO in mid-September provided greater leafy spurge control compared to August or October applications.

Field studies were conducted from 1995 through 1998 to evaluate citronmelon control with postemergence (POST) herbicides. Imazapic at any application timing and late postemergence (LPOST) applications of 2,4-DB were the only herbicides that provided >80% control of citronmelon late season. Other herbicides such as acifluorfen, imazethapyr, lactofen, and pyridate provided acceptable (>75%) early-season control of citronmelon, but control was inadequate at harvest.

Field experiments were conducted to determine the influence of nozzle type, spray volume, and adjuvants on herbicide efficacy. Carfentrazone and imazamox, representing contact and translocated herbicides, respectively, were equally or more effective when applied with drift-reducing TurboDrop or Drift Guard nozzles than the conventional flat-fan nozzle in 95% of the comparisons. Imazamox was equally effective when applied in 47, 94, or 190 L/ha spray volume, regardless of nozzle type or adjuvant. Carfentrazone applied in 47 L/ha spray volume controlled flax and sunflower as well as in 94 or 190 L/ha, provided urea ammonium nitrate fertilizer and either nonionic surfactant or methylated vegetable oil were included in the spray mixture. Conversely, carfentrazone with only urea ammonium nitrate was less effective when applied in 47 than in 94 or 190 L/ha spray volume. Carfentrazone and imazamox applied in low spray volumes (47 L/ha) gave consistent control when an effective adjuvant was included in the spray mixture.

Field research was conducted at three locations in Iowa to determine the effectiveness of glyphosate for velvetleaf control in glyphosate-resistant soybean. Velvetleaf survival ranged from 46 to 81% when treated with 420 g ae/ha glyphosate, whereas survival ranged from 13 to 37% at the 840 g/ha rate. At two locations, velvetleaf survival was greater when treated at the 12- to 17-cm height compared with application to either 8- to 10- or 20- to 30-cm-tall plants. Growth of plants surviving glyphosate application was greatly reduced, with the high glyphosate rate reducing velvetleaf aboveground biomass by over 90% compared to untreated plants. A linear relationship between biomass and capsule number was observed for both control plants and plants surviving glyphosate, both having slopes of approximately one. Velvetleaf surviving glyphosate treatment should have minimal impact on soybean yield due to reduced growth; however, surviving plants may replenish the seed bank, leading to future management problems.

A field experiment was conducted over 2 yr to study efficacy of bromoxynil mixtures with pyrithiobac or MSMA applied postemergence (POST) with and without fluometuron or fluometuron plus pendimethalin preemergence (PRE) for control of broadleaf weeds in ultra narrow row bromoxynil-resistant cotton in the Mississippi Delta. Bromoxynil applied POST (single or sequential) provided variable control of common purslane (<9%), sicklepod (<35%), Palmer amaranth (<46%), prickly sida (>75%), hyssop spurge (>79%), hemp sesbania (>96%), and pitted morningglory (100%) at 4 wk after early POST (WAT). Broadleaf weed control increased when PRE herbicides were followed by bromoxynil or bromoxynil plus pyrithiobac or MSMA POST. Weed control generally decreased at harvest compared to 4 WAT, and the decrease was greater in bromoxynil POST-only programs compared to bromoxynil POST following PRE programs. Seed cotton yield with bromoxynil POST-only programs was lower (400 to 2,810 kg/ha) compared to bromoxynil POST programs following PRE herbicides (2,150 to 3,720 kg/ha). Early-season weed interference and variable control of weeds in bromoxynil POST-only programs resulted in greater cotton stand reduction and lower open bolls per plant compared to bromoxynil POST programs following PRE herbicides.

Desiccants are used in potato production to remove vines before harvest to make harvest easier. We evaluated the new herbicide glufosinate-ammonium for potential as a vine desiccant, for its effect on seed tuber sprouting, and plant growth the following season. Glufosinate-ammonium was applied at 0, 0.3, 0.45, 0.6, and 0.75 kg ai/ha and compared with diquat at 0.84 kg ai/ha when applied as desiccants in mid-September in 1997 and 1998. Potato leaf and vine desiccation were rated 3, 7, and 14 d after treatment (DAT). Yields were obtained at maturity and tubers retained and stored over winter at 3 C and 95% relative humidity for determination of stem end discoloration (SED), tuber sprouting in March, and plant growth of daughter tubers planted the following year. Application of glufosinate-ammonium resulted in slower leaf and stem desiccation at 3 and 7 DAT than did diquat. By 14 DAT leaf desiccation was the same but stem desiccation was slightly less than with diquat. Tuber SED and marketable tuber yield were no different with either desiccant. At higher rates of application, glufosinate-ammonium reduced daughter tuber sprout weight but had no effect on number of sprouts in growth room sprouting tests when compared with untreated controls. Daughter tubers from glufosinate-ammonium-treated plants planted the next growing season had markedly slower emergence and established full emergence 7 to 14 d later than diquat-desiccated tubers.

Field studies were conducted with fresh market spinach to examine crop tolerance and weed control with S-metolachlor. S-metolachlor was applied preemergence (PRE) at rates of 0.56, 0.72, 1.06, and 1.41 kg/ha and compared with the commercial standard cycloate at 3.4 and 4.5 kg/ha. Spinach was generally tolerant of S-metolachlor at rates up to 1.06 kg/ha on all soil types. S-Metolachlor at 0.56 to 0.72 kg/ha and cycloate at 3.4 kg/ha provided >88% control of common purslane, nettleleaf goosefoot, and shepherd's purse. Control of common chickweed with S-metolachlor at ≥0.56 kg/ha was >80%, whereas cycloate at 3.4 to 4.5 kg/ha was ineffective. Hand-weeding times in plots treated with S-metolachlor at 0.56 and 0.72 kg/ha were similar or lower than hand-weeding times in plots treated with cycloate at 3.4 kg/ha. Greenhouse studies were conducted to compare the relative tolerance of fresh market spinach to S-metolachlor and metolachlor. The GR10 values for S-metolachlor and metolachlor were 1.57 and 2.03 kg/ha, respectively. At rates above 2.2 kg/ha S-metolachlor is less selective in spinach than metolachlor. S-metolachlor is safe for PRE use in fresh market spinach at rates up to 1.06 kg/ha.

Early canopy closure and manipulation of crop row spacing or density can reduce the amount and frequency of herbicide use in corn. Field studies were conducted at Woodstock, ON from 1996 to 1999 to evaluate the effect of corn row spacing, plant density, and frequency of glufosinate application on weed biomass and corn yield in glufosinate-resistant corn. Treatments included row width, corn density, and herbicide. The effect of row width and corn density on weed biomass was variable among years. In a wet year (1996), narrow (38 cm) rows provided greater weed suppression than wide (76 cm) rows regardless of crop density. In a dry year (1998), narrow-row high-density (100,000 plants/ha) corn had the lowest weed biomass. In other years, either narrow row or high density was equally successful in suppressing weeds. Effectiveness of herbicides in reducing weed biomass was not influenced by row width or corn density. Corn yield was influenced by row width or corn density. Although weed biomass was lowered by two applications of glufosinate in comparison with a single application, corn grain yields were similar between the two treatments. Planting corn at higher densities may help in reducing early-season weed competition, whereas narrow rows may help in controlling later-emerging species.

Dicamba is a herbicide used for the control of broadleaf weeds in wheat. Dicamba, applied within the recommended growth stage interval, reduced the grain yield of Wakefield winter wheat by 95% in a herbicide sensitivity study at Michigan State University. Growers have also reported yield loss when using dicamba on Wakefield. Field and greenhouse experiments were conducted to characterize the response of Wakefield winter wheat to dicamba and to compare this response to that of ‘Harus’ winter wheat, a cultivar that is not considered sensitive to dicamba. This research was conducted to characterize the sensitivity of Wakefield to dicamba and to develop visual methods for detecting sensitivity of wheat cultivars to dicamba. Field experiments confirmed that dicamba affects the number of spikelets and the seed weight of Harus and Wakefield similarly. However, dicamba, applied within the recommended application interval, caused small, shriveled (underdeveloped) seeds to occur in Wakefield in the field and greenhouse. These seeds weighed very little, did not contribute to grain yield, and could not be harvested mechanically. Dicamba reduced the number of fully developed seeds of Wakefield by as much as 62% in the field and 92% in the greenhouse when applied within the recommended application interval. The number of fully developed seeds of Harus was reduced in the field only when dicamba was applied later than the recommended application interval. Decreases in grain yield due to dicamba were caused primarily by decreases in the number of fully developed seeds. Greenhouse experiments indicated that pollen abnormalities were only a minor cause of the development of underdeveloped seeds.