Spray droplet size of water and paraffinic oil was affected by air pressure, nozzle type, and liquid flow rate when applied with an ultralow volume (ULV), air-assist sprayer. Volume median diameters of water were generally larger than oil at constant air pressure and liquid flow rate. Droplet size decreased as air pressure increased, but increased as liquid flow rate increased. Volume median diameters of water droplets ranged from 41 to 838 μm and from 16 to 457 μm with oil when atomized at air pressures ranging from 14 to 84 kPa. Relative spans ranged from 1.2 to 18.0 and 2.0 to 7.2 for water and oil, respectively.

Four experiments (three in Macedonia, Greece and one in Holtville, CA) were conducted in 1988 and 1989 to evaluate foliar applications of picloram, glyphosate alone and with adjuvant, and triclopyr for the control of established silverleaf nightshade. Silverleaf nightshade control was determined by comparing stem population at the time of herbicide application to stem population 6 to 11 mo after application. Picloram, averaged over rate and location, controlled silverleaf nightshade consistently, restricting regrowth to less than 5%. Silverleaf nightshade control with glyphosate alone or with adjuvant varied with location, regrowth ranged from 0 to 69%. Regrowth of silverleaf nightshade treated with triclopyr approached that of the untreated control.

Fluazifop-P, sethoxydim, and quizalofop were evaluated over two years for postemergence annual grass control in sweet potatoes. All treatments controlled broadleaf signalgrass and large crabgrass, but in 1987 only rates of at least 0.14 kg/ha of fluazifop-P and quizalofop and 0.28 kg/ha of sethoxydim controlled large crabgrass. No. 1 grade and total yield were greater from plots treated with herbicides compared with the weedy check in 1986. In 1987, No. 1 grade and total yield were greater in plots treated with fluazifop-P at 0.14 kg/ha or higher and sethoxydim or quizalofop at 0.28 kg/ha or higher.

Field experiments were conducted using a stale seedbed production system to determine the effect of herbicide application time on preplant, preplant incorporated (PPI), and at-planting treatments on weed control and soybean yield. Herbicides were applied on the surface preplant (PPL) or PPI at 6 to 7, 4 to 5, and 2 to 3 wk before planting and just prior to planting. The differences in weed control and soybean yield among years were due to rainfall patterns 2 wk after herbicide application and during the growing season. Preplant treatments applied 2 to 5 wk before planting generally controlled common cocklebur and pitted morningglory better than preplant treatments applied 6 to 7 wk before planting due to persistence of herbicide activity or treatments at planting due to a greater chance of obtaining adequate rainfall for herbicide activation, more uniform seedbed at planting, and larger weeds at application. Metribuzin plus chlorimuron was less suited than imazaquin as a preplant treatment when applied more than 2 weeks before planting.

Field experiments were conducted to determine the occurrence and the extent of interaction among four soil-applied organophosphate insecticides and the sulfonylurea herbicide nicosulfuron applied POST to corn. Nicosulfuron was damaging to corn when the crop was planted with terbufos, phorate, or fonofos applied into the open furrow. Terbufos was the most damaging and also caused damage when applied as a 17-cm band prior to or after closing the furrow, with or without incorporation. Phytotoxic symptoms appeared within 3 d of application of nicosulfuron and damage increased as the rate was increased from 53 g ai/ha to 140 g ai/ha. However, despite severe damage of up to 50% recorded in some terbufos combinations, all plants had completely recovered within 4 wk and none of the treatments had any effect on grain yield or crop maturity. No damage resulted from nicosulfuron when corn was planted with the insecticide chlorpyrifos. Efficacy data of nicosulfuron on the main weeds present are also reported.

Field studies were conducted in northern Tamaulipas, Mexico in 1991 and 1992 to determine the effectiveness of POST applications of primisulfuron and nicosulfuron on shattercane control in corn. Primisulfuron at 15 g/ha and nicosulfuron at 30 g/ha were the minimal doses required for shattercane control. Both herbicides applied on 5- to 9-leaf shattercane provided excellent (> 90%) control 35 d after application. No corn injury was evident with any herbicide and rates evaluated. Untreated check plots sustained 30 to 56% of yield reduction as compared to herbicide treatment plots.

Experiments were conducted in 1991 and 1992 to evaluate annual grass and broadleaf weed control with bromoxynil applied alone and with graminicides. Bromoxynil controlled velvetleaf better than entireleaf morningglory and controlled both species better than sicklepod. Mixing bromoxynil with fluazifop-P, quizalofop-P, and sethoxydim reduced control of barnyardgrass, green foxtail, large crabgrass, and shattercane. Control of broadleaf signalgrass with quizalofop-P was reduced by bromoxynil. Annual grass control with clethodim was not affected by bromoxynil.

'Silver Xtra Sweet’, ‘How Sweet It Is', ‘Zenith’ and 'Sweetie 76’ were evaluated for response to 0, 35, and 70 g/ha nicosulfuron applied POST at the 5- to 6- or 7- to 8-leaf stages of growth. Nicosulfuron (35 g/ha) caused 60 to 80% visible injury to Silver Xtra Sweet. How Sweet It Is and Zenith were moderately tolerant (< 20% visible injury) and Sweetie 76 was the most tolerant (10% visible injury). All cultivars were less tolerant when nicosulfuron was applied at the 7- to 8-leaf than the 5- to 6-leaf stage. Plant height of Silver Xtra Sweet was reduced 51% by 35 g/ha nicosulfuron applied at the 5- to 6-leaf stage and injury increased when nicosulfuron was applied at the 7- to 8-leaf stage. Yield losses of Silver Xtra Sweet occurred as a result of the nicosulfuron treatments.

Field studies were conducted at Carbondale and Belleville, IL to evaluate weed control in corn with a total POST herbicide program. Nicosulfuron was applied at 24 and 35 g/ha alone and in combination with 2,4-D, dicamba, bromoxynil, bentazon, atrazine, and bentazon, bromoxynil, and dicamba plus atrazine. Nicosulfuron controlled 98 to 100% of giant foxtail both years at both locations. Control of giant foxtail was reduced when nicosulfuron at 24 g/ha was applied as a tank-mix with atrazine, and with bentazon, bromoxynil, or dicamba plus atrazine at Belleville in 1991. Also, bentazon plus atrazine with nicosulfuron at 35 g/ha reduced control of giant foxtail. Control of common lambsquarters, jimsonweed, and velvetleaf was dependent on nicosulfuron rate, companion herbicide, and growing conditions. Nicosulfuron alone or as a tank-mix with the companion herbicides controlled redroot pigweed 100% at both sites both years but control of yellow nutsedge was less than 50%. Corn yield was related to level of weed control obtained in most instances.

Ten field experiments were conducted in Oklahoma from 1988 to 1992 to evaluate chlorsulfuron plus metsulfuron (5:1 w/w) and triasulfuron for cheat control in winter wheat. Cheat control by chlorsulfuron plus metsulfuron at 18 and 26 g ai/ha varied from 0 to 81% and by triasulfuron at 18 and 30 g ai/ha from 0 to 60%. Grain yield was increased in four experiments and dockage was reduced in five experiments by both rates of chlorsulfuron plus metsulfuron.

Studies were conducted in 1988, 1989, and 1992 in Plains, GA to measure effects of paraquat and alachlor on ‘Florunner’ peanut. Peanut treated with paraquat (0.14 kg ai/ha) plus alachlor (3.4 kg ai/ha) applied at vegetative emergence (VE), or paraquat plus alachlor VE followed by paraquat 28 days after emergence (DAE) were compared with a nontreated control. Both herbicide treatments reduced peanut foliage biomass at 65 DAE in 1989 and 1992. Herbicide treatments did not affect foliage biomass 90 DAE in 1988 and 122 DAE in 1989, but paraquat plus alachlor followed by paraquat reduced foliage biomass at 122 DAE in 1992. Pod biomass, measured at 90 and 65 DAE in 1988 and 1992, respectively, was reduced by herbicides. However, pod biomass did not differ among treatments 122 DAE in 1989 and 1992. Percent reflectance from the peanut canopy measured no effects from herbicides in 1988. However, in 1989 and 1992 herbicides applied sequentially reduced peanut canopy development. Peanut treated with a single herbicide and sequentially took longer to mature. Once optimum maturity was reached, peanut yields were not reduced.

Trifluralin selectively controls dodder in alfalfa. However, its soil activity dissipates allowing some late season dodder germination. Thiazopyr applied PRE was also found to control dodder selectively in alfalfa. Thiazopyr was more effective when applied in February than in November. Thiazopyr did not control dodder longer into the season than trifluralin in field tests, however it was more effective in greenhouse experiments. The effect of thiazopyr on dodder shoot tips was similar to that of trifluralin, in that both herbicides produced bulbous cells with thickened, globular nuclei, typical of cells treated with herbicides affecting microtubules.

False broomweed is a troublesome weed on south Texas rangelands. The plant suppresses the growth of desirable herbaceous plant species and is unpalatable to livestock and wildlife. The objectives of this study were to evaluate multispectral satellite data for automated detection, classification, and mapping of false broomweed infestations. Determining the optimum phenological conditions for false broomweed detection was a major goal. Results indicate that satellite data can be used to detect major stands of this shrub and map the relative extent of infested areas. The best classification was obtained when the foliage of the shrub was fully developed and during periods of low herbaceous biomass production. Limited ground or aerial surveying will be needed to produce more exact estimates of the extent of false broomweed stands; however, these efforts can be focused on areas identified by satellite classification.

Field studies were conducted in 1991 and 1992 to evaluate the duration of giant foxtail control in no-till soybean with MON 13200 alone and with imazaquin applied up to 2 mo prior to planting. MON 13200 at rates ranging from 224 to 448 g ai/ha applied up to 57 d before planting controlled 97 to 99% of giant foxtail averaged over years. MON 13200 plus imazaquin applied approximately 45 or 30 d before planting controlled 92 to 99% of giant foxtail compared with 53, 64, and 65% and 61, 69, and 78% in plots treated with alachlor, metolachlor, or pendimethalin plus imazaquin, respectively. Differences in control of giant foxtail among the herbicides evaluated were minimal when applied 15 or 0 d before planting. Little or no soybean injury was observed in 1991; up to 30% was observed in 1992 but final soybean height was not affected.

Weed management treatments with various degrees of herbicide inputs were applied with or without a hairy vetch cover crop to no-tillage corn in four field experiments at Beltsville, MD. A hairy vetch living mulch in the no-treatment control or a dead mulch in the mowed treatment improved weed control during the first 6 wk of the season but weed control deteriorated in these treatments thereafter. Competition from weeds and/or uncontrolled vetch in these treatments without herbicides reduced corn yield in three of four years by an average of 46% compared with a standard PRE herbicide treatment of 0.6 kg ai/ha of paraquat plus 1.1 kg ai/ha of atrazine plus 2.2 kg ai/ha of metolachlor. Reducing atrazine and metolachlor to one-fourth the rate of the standard treatment in the absence of cover crop reduced weed control in three of four years and corn yield in two of four years compared with the standard treatment. Hairy vetch had little influence on weed control or corn yield with any herbicide treatments.

Field studies were conducted near Beechwood, WI in 1986 and Sturgeon Bay, WI in 1987 and 1988 to evaluate herbicide treatments for control of triazine-resistant common lambsquarters (TR-CHEAL) in corn. AH PRE and many early postemergence (EP) and POST treatments were less effective in 1988 than in 1986 or 1987 due to drought. Atrazine, cyanazine, and metolachlor PRE controlled less than 15% TR-CHEAL late-season over the three years. Dicamba or pendimethalin applied PRE controlled 88 to 99% late-season TR-CHEAL in 1986 and 1987. Late-season TR-CHEAL control in 1986 and 1987 from acetochlor plus atrazine, alachlor plus atrazine, and metolachlor plus linuron applied PRE ranged from 58 to 86%. Pendimethalin plus cyanazine or atrazine applied EP controlled TR-CHEAL 97% or more late-season in 1986 and 1987, while pendimethalin plus dicamba plus atrazine applied EP controlled TR-CHEAL 97% or more each year. Late-season TR-CHEAL control from tridiphane plus cyanazine or atrazine EP was less than 58%. Late-season TR-CHEAL control from dicamba, 2,4-D amine, pyridate, and thifensulfuron applied POST was 87 to 99% each year, and was 94 to 99% in 1986 and 1987 from bromoxynil or bentazon applied POST. Dicamba, thifensulfuron, pendimethalin, pyridate, and 2,4-D amine were most effective in controlling TR-CHEAL in corn.

The effect of duration of wild oat competition on spring wheat yield and growth was determined in time-of-removal experiments conducted over a three year study period in Saskatchewan, Canada. Failure to remove wild oat reduced wheat yield 28 and 39% at wild oat populations of 64 and 188 plants per m2, respectively. Wheat yield was not reduced by wild oat densities of 64 or 118 plants per m2 until the six- and seven-leaf stage of wild oat, respectively. Removing wild oat at 64 plants per m2 before the seven-leaf stage and 118 plants per m2 before the five-leaf stage did not increase wheat culm or fresh weight production.

Metolachlor, applied to the surface of leaching columns as dicalcium phosphate tablets, was recovered over a period of 25 d compared with 2 and 3 d for emulsifiable concentrate and granular formulations, respectively. In similar studies, approximately 27% of napropamide was recovered from tablets during the same period. Adding an adjuvant to the napropamide tablet mixture increased the recovery rate to 55%. Tablet hardness and size had little effect on the release rate of napropamide. Tablets containing 4% ai napropamide released greater amounts of herbicide at a single collection period than did tablets containing 1% ai. Adding an adjuvant to the napropamide tablet mixture significantly improved Italian ryegrass control in the area adjacent to herbicide placement.

Greenhouse studies were conducted to determine the response of purple and yellow nutsedges to selective soil placement of 5 cm of soil treated with imazethapyr above and/or below the nutsedge tubers. Early postemergence (EPOST) or postemergence (POST) imazethapyr treatments at 71 g ai/ha as a foliar, soil, or foliar + soil application was also evaluated. Imazethapyr placement above or below the nutsedge tuber generally increased shoot number, shoot dry weight (SW), shoot regrowth dry weight (SRW), and root tuber dry weight (RTW) production in both species, 28 and 42 days after treatment (DAT) compared with the control. However, the 5-cm above + 5-cm below tuber treatment at 14, 28, and 42 DAT reduced purple nutsedge shoot number, SW, SRW, and RTW to 19, 7, 14, and 26% of the control, respectively. Yellow nutsedge shoot number was 103% of the control with the 5-cm above + 5-cm below tuber treatment 42 DAT. The 5-cm above + 5-cm below tuber treatment reduced yellow nutsedge SW, SRW, and RTW to 43, 44, and 23% of the control, respectively, 28 and 42 DAT. EPOST and POST foliar + soil and soil-only applications reduced SW 28 d after treatment (DAT) to 13% or less of the control for both species. SRWs of both species were ≤ 53% of the control 42 DAT for the soil-only application. The foliar-only treatment was the least effective in SW, SRW, and RTW reductions.