Extension workers are sensing pressure to use soils information and chemical characteristics data to guide farmers in selecting pesticides least prone to leach into groundwater. Our objective was to estimate differences in herbicide migration to groundwater under conditions typical for the Southeast Coastal Plain, and to consider how a farmer might be advised to use such knowledge in selecting herbicides. We used a simple computer code for microcomputers to predict persistence and migration of 17 herbicides through a hypothetical, coarse-textured soil typical of the Southeast Coastal Plain. Appropriate herbicides were selected for several common crop-weed problems, such as sicklepod in soybean and Palmer amaranth in corn. Groundwater was assumed to be 3.15 m below the soil surface. Herbicides selected covered a broad range of half-lives and organic carbon partition coefficients. Only after the first-order degradation rate constant was reduced by a factor of five did predicted soil water concentrations of several herbicides at the groundwater interface reach normal detection limits. Still, predicted concentrations were below the level established for health effects advisory purposes. Due to the large number of uncertainties and the inability to estimate practical benefits, we conclude that data relating to soil and herbicide characteristics cannot be used at this time to override cost effectiveness, efficacy, and other factors normally considered by farmers and Extension professionals in herbicides for weed control.

Barnyardgrass 7 to 25 cm tall was controlled 48 to 74% with paraquat (420 g/ha), 83 to 87% with glyphosate (1120 g/ha), and 85 to 91% with glufosinate (840 g/ha). In most cases barnyardgrass control was not enhanced with addition of residual herbicides metribuzin plus chlorimuron, metribuzin, or imazaquin. Barnyardgrass and seedling johnsongrass no more than 13 cm tall was controlled at least 90% regardless of herbicide treatment. When rhizome and seedling johnsongrass were present, control with glyphosate was 96% compared with 55% for paraquat and 86% with glufosinate. Tank-mixtures of non-selective and residual herbicides generally enhanced control of entireleaf and pitted morningglory, hemp sesbania (15 to 30 cm), and prickly sida (15 to 18 cm). Soybean yields in most cases were not increased with addition of residual herbicides. Yield following glufosinate applied alone was 25% higher than following paraquat, and for all herbicide treatments yields were at least 45% greater than when a non-selective herbicide was not applied.

Field experiments conducted in 1988 and 1989 evaluated clomazone alone and in a systems approach for weed control in peanut. Clomazone PPI at 0.8 kg ai/ha controlled common ragweed, prickly sida, spurred anoda, and tropic croton better than ethalfluralin and/or metolachlor applied PPI. POST application of acifluorfen plus bentazon was not needed to control these weeds when clomazone was used. Acifluorfen plus bentazon improved control of these weeds when clomazone was not used and generally were necessary to obtain peanut yields regardless of the soil-applied herbicides. Alachlor PRE did not improve clomazone control of any weed species evaluated. Fall panicum and large crabgrass control was similar with clomazone or clomazone plus ethalfluralin.

Field experiments conducted over three years at Stoneville, MS evaluated invert emulsion and oil diluents on the efficiacy of glyphosate and MSMA on purple nutsedge. The herbicides were applied at 0.6 and 1.1 kg ai/ha in an invert emulsion (oil-in-water) and a paraffinic oil at 19 L/ha (low-volume) and in water with a non-ionic surfactant (0.25% v/v) at 187 L/ha (high-volume). Purple nutsedge control with both herbicides was greater with the low-volume, invert emulsion and oil diluent applications than with high-volume, water diluent applications. Glyphosate and MSMA at 1.1 kg/ha in the oil diluent controlled purple nutsedge at least 88% when compared with the invert emulsion (≥ 75 and ≥ 76%, respectively) and water (≥ 42 and ≥ 44%, respectively) diluents. Cotton injury and seed cotton yields were unaffected by any treatment with MSMA but glyphosate with each diluent caused unacceptable cotton injury and seed cotton yield reduction.

The absorption and translocation of the isopropylamine salts of 14C-glyphosate and 14C-imazapyr were compared in established terrestrial alligatorweed. Results indicated that more than twice as much imazapyr as glyphosate was absorbed by treated leaves of alligatorweed. In addition, more imazapyr was translocated to the underground storage tissues in alligatorweed than was glyphosate. This difference in translocation to roots and subterranean storage tissues is proposed as a mechanism for tolerance of alligatorweed to glyphosate and susceptibility to imazapyr.

Laboratory and field experiments were conducted to determine whether manipulation of radiation environment during the period of winter wheat establishment can be used to improve wheat yields in Italian ryegrass-infested fields. Percentage of total irradiation and ratio of red (R) light (around 660 ηm) to far-red (FR) light (around 730 ηm) reaching the soil surface were important factors in regulating Italian ryegrass germination, growth, and competitive interactions with wheat. Reducing total irradiation to about 10% of full sunlight while maintaining the normal R/FR ratio of about 1.0 reduced wheat grain production in the presence of Italian ryegrass by about 40% compared with weed-free wheat in full sunlight. Further, reducing total irradiation to 3% of full sunlight plus reducing the R/FR ratio to about 0.2 reduced wheat grain production competing with Italian ryegrass by about 35% compared with production in the control conditions. Wheat production of dry matter, spikes, and seeds in the presence of Italian ryegrass increased more than threefold under both shading treatments compared with production in full sunlight.

The influence of PRE herbicides on rooting characteristics of bermudagrass turfgrass was studied using sod plugs removed from the field. Greenhouse root fresh weight was reduced the greatest with dithiopyr or prodiamine. Pendimethalin caused fewer fresh weight reductions compared to dithiopyr or prodiamine and these reductions were usually for a short period. Root weight loss was due to lower root density and root malformation. Significant numbers of malformed roots were also observed for greater periods of time where dithiopyr or prodiamine had been applied.

Detectspray™ weed-activated sprayer (WAS) technology enables individual nozzles on a sprayer to turn on and off in response to the presence of green vegetation. WAS operated full season at two fallow sites in North Dakota reduced POST herbicide requirement 47 to 88%. Full-season WAS applied as needed at West Fargo reduced cost to the farmer by only 13% compared with broadcast application with a farmer-owned sprayer and assuming free labor. Winds of 8 to 16 km/h apparently moved spray off target, thereby necessitating retreatment and increasing the relative costs of WAS at Fargo. The percentage of sample quadrats having greater than 3% vegetative cover correlated positively (r = 0.78 to 0.80) with percentage reduction in spray volume achieved by WAS.

Imazapyr, imazaquin, and imazethapyr were evaluated for control of leafy spurge. Herbicides were applied at 70, 140, and 280 g ae/ha in Fall 1989, 1990, or 1991 on a sub-irrigated meadow near Ainsworth, NE and a tallgrass prairie near Columbus, NE. Imazapyr, imazaquin, imazethapyr at 280 g/ha controlled leafy spurge 58, 82 and 73%, respectively, 9 mo after treatment (MAT) at Ainsworth. Leafy spurge control averaged 49% 9 MAT at Columbus where 280 g/ha of the imidazolinone herbicides were applied. Leafy spurge yields were reduced at Ainsworth by 29 and 78% where the imidazolinones were applied at 140 and 280 g/ha. By 11 MAT, leafy spurge control on areas treated with 280 g/ha declined to less than 60% at Ainsworth and 10% at Columbus. Perennial forage grass yields at both sites were generally unaffected by imazaquin or imazethapyr, but imazapyr at 280 g/ha reduced yields by 69 and 44% at Ainsworth and Columbus, respectively. Imidazolinone herbicides applied in the fall partially controlled leafy spurge, but did not increase perennial forage grass yields.

Winter wheat grain contaminated with jointed goatgrass joints is often discounted as much as 20% by grain buyers. A mail survey to Nebraska farmers in 1984 identified jointed goatgrass as one of the ten worst weed problems in winter wheat, but a field survey to the same area in 1986 found it in less than 1% of surveyed fields. The objective of this survey was to map the geographic distribution and severity of jointed goatgrass contaminating winter wheat grain in western Nebraska. Jointed goatgrass was found in 25, 29, and 20% of all wheat samples collected in 1990, 1991, and 1992, respectively. Nebraska counties bordering Colorado were found to have the highest percentage of wheat samples contaminated with jointed goatgrass joints, ranging from 23% in Cheyenne county in 1992 to 61% in Keith county in 1991.

Field studies were conducted from 1987 through 1990 on Sharkey clay to determine effect of weed control treatment (WTRT) on yield and net return from soybean grown with no irrigation (NI) or irrigation (I) during reproductive development. Weed control treatments were: 1) PRE glyphosate plus metribuzin plus metolachlor or pendimethalin, followed by POST bentazon plus acifluorfen or 2,4-DB plus linuron (high WTRT); 2) PRE glyphosate at a rate to kill existing weeds at planting (medium WTRT); or 3) PRE paraquat at a rate to desiccate but not necessarily kill existing weeds at planting (low WTRT). POST cultivation was used in all treatments. Weed ground cover in the high, medium, and low WTRT's was composed of annual grass and moderately competitive broadleaf species, and averaged 7, 25, and 49%, respectively, at harvest in 1990. Yield declined with decreasing weed control in the I treatment after the first year, but average net returns from the high and medium WTRT's were not different, and both exceeded average returns from the low WTRT. Yields from the high and medium WTRT's in the NI treatment were not different, and both exceeded yield from the low WTRT. Average net returns from the medium WTRT were greater than those from the high and low WTRT's in all years. Yield increase from irrigation and difference in average net returns between I and NI declined with decreasing weed control.

Sicklepod control mid-season in cultivated soybean was higher when imazaquin plus AC 263,222 or AC 263,222 alone was applied POST following pendimethalin plus imazaquin PPI compared with only the PPI treatment. Pendimethalin plus imazaquin PPI followed by imazaquin plus AC 263,222 at 36 + 18 g ai/ha or followed by AC 263,222 at 18 g ai/ha with cultivation controlled sicklepod equal to pendimethalin PPI followed by imazaquin plus AC 263,222 at 71 + 18 g ai/ha or followed by a sequential application of AC 263,222 at 13 g ai/ha early POST followed by 9 g ai/ha late POST. Control with these treatments was no higher than for the standard of pendimethalin plus metribuzin PPI followed by chlorimuron POST at 9 g ai/ha, which controlled 86% sicklepod. Averaged across herbicide treatments, cultivation reduced percent sicklepod seed in harvested soybean samples 33% and increased soybean yield 19% compared with no cultivation. Soybean yield was highest for the chlorimuron standard and greater than that for the other treatments when averaged across cultivation treatments.

The influence of green kyllinga and white kyllinga on common bermudagrass growth was compared by planting one to three green or white kyllinga rhizomes with two bermudagrass stolons. White kyllinga reduced bermudagrass shoot fresh weight to 56% of the control, but green kyllinga did not reduce bermudagrass shoot fresh weight significantly. Increased planting densities of both kyllinga species linearly increased kyllinga shoot fresh weight and decreased bermudagrass shoot fresh weight similarly. White kyllinga produced more leaf fresh weight, leaf area, and roots and rhizomes than green kyllinga, which produced more shoots and inflorescences.

Commercially available cabinet sprayers are not well suited for making low volume applications (<30 L/ha) of herbicides to woody forest species that can be up to 1.5 m tall. A simple, inexpensive laboratory sprayer that overcomes some limitations of commercial cabinet sprays can be built from materials readily available at local building and electronic suppliers. The only specialized equipment required is a positive displacement pump and a rotary disk atomizer. The atomizer is attached to the end of a variable height arm mounted on a laboratory cart. A positive displacement pump ensures controlled flow. The operator pushes the cart along a metal rub rail which keeps the cart tracking in a straight line. Travel speed is regulated by the operator following a marker on a clothesline-like loop of fishing line and is driven by a variable-speed drill attached to a variable voltage power supply.

Absorption of 14C-bentazon from the leaf surfaces of common cocklebur and velvetleaf was rapid and most occurred within 4 h after foliar application. Greater 14C in the epicuticular wax (ECW) did not correlate with higher radioactivity in the leaf tissue. There was significantly less ECW on the “mature” leaves of common cocklebur and “juvenile” leaves of velvetleaf. However, the “mature” leaves exhibited greater 14C absorption for both species. The use of 28% urea ammonium nitrate increased 14C-absorption when compared with crop oil concentrate and with no adjuvant.

DC X2-5309 organosilicone adjuvant added at 1% (v/v) spray solution increased the efficacy of bentazon, pyridate, and terbacil on kochia in greenhouse trials. DC X2-5309 decreased the rain-free period needed after application of bentazon and bromoxynil to 6 and 1 h, respectively, and increased the uptake of 14C-bentazon and 14C-bromoxynil by kochia at 1, 3, 6, and 24 h after application compared with crop oil concentrate (COC). In field trials, bentazon and bromoxynil rates required to control equal amounts of kochia were reduced by half when adding DC X2-5309 compared with adding crop oil concentrate. DC X2-5309 added at 0.5% (v/v) spray solution with bentazon did not injure spearmint and controlled kochia equal to or better than bentazon with COC added at 1% (v/v) spray solution.

Field experiments were conducted in 1990, 1991, and 1992 to evaluate and compare the efficacy of commercial herbicide formulations with starch encapsulated granules that contain one, two, or three herbicides. Atrazine in combination with alachlor or metolachlor composed the two-component granules and the addition of dicamba to both composed the three-component granules. All starch-encapsulated formulations were produced by twin screw extrusion technology and evaluated in two granule sizes, 1.4 to 0.5-mm (14 to 20 mesh) and 0.85 to 0.43-mm (20 to 40 mesh). Active ingredient rates applied were selected for the existing soil conditions and combination granules contained active ingredients proportional to premixed commercial formulations available or suggested for tank mixes. Evaluations were performed under conventional, chisel, and no-tillage systems. PRE and PPI applications of starch encapsulated two-component (atrazine-alachlor) in 1990 controlled giant foxtail (except at the low rate with large granule size), redroot pigweed, and common lambsquarters excellently but control of velvetleaf was fair to poor. Smaller-sized granules were generally more effective for controlling weeds than the larger-sized granules. In 1991, starch-encapsulated two-component (atrazine-metolachlor) granules applied both PRE and PPI in conventional, chisel, and no-till systems gave results similar to 1990 with the small granules more effective on velvetleaf. The addition of dicamba in the granule to form three-component starch-encapsulated granules in 1992 resulted in control of velvetleaf, ivyleaf morningglory, and jimsonweed statistically equal to commercial formulations except in one case of no-till corn. In our experiments, herbicide formulations (granular vs. commercial) had no significant effect on corn yield in 28 out of 31 treatments. These data indicate that if the experimental three-component starch-encapsulated formulations of corn herbicides used in these studies were optimized they could become as efficacious as commercial formulations presently on the market. This is the first report of research containing data on two- and three-component starch-encapsulated granular formulations.

Herbicide efficacy trials in field corn, sweet corn, and soybean were conducted at three locations in Wisconsin over a 6-yr period. Percent weed pressure (WP) was determined by visually estimating the contribution of all weed species present to the total crop and weed volume in each plot. Crop yields in each plot were measured. Percent crop yield reduction (YLDRED) was calculated by comparing mean yields of individual treatments with those of the highest yielding treatment in each trial. Linear regression analyses of YLDRED and WP data from 1640 field corn and 138 sweet corn treatments were significant. Nonlinear regression analysis of YLDRED and WP data from all 1374 soybean treatments was significant; however, a linear regression of those 1154 soybean treatments with WP ratings of 30 or less produced a more easily interpreted regression equation.

The response of ‘Florico,’ ‘Victoria,’ and 'Stan II’ triticale to 2,4-D, dicamba, 2,4-D plus dicamba, diclofop, and thifensulfuron plus tribenuron applied POST during the tillering stage was examined. At rates twice those recommended for application to wheat, Victoria and Stan II were not injured, and injury to Florico was less than 10%. None of the herbicides or combinations adversely affected plant height at maturity, tiller or spike production, grain weight/spike, kernel weight, kernels/spike, yield, or test weight of any cultivar. Cultivars varied in tiller production, height, yield, test weight, kernel weight, and kernels/spike.