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.

Triclopyr (0.28, 0.56, and 1.12 kg ai ha−1); triclopyr + 2,4-D (0.56 + 1.12 kg ha−1); and dicamba (1.12 kg ha−1) were evaluated over 2 yr at two locations in Florida for southern wax myrtle control following spring (Mar. to Apr.) or summer (Aug. to Sept.) applications. All treatments were applied twice, 1 yr apart, except 1.12 kg ha−1 triclopyr, which was applied once in the initial year. In the first year, defoliation with triclopyr was quadratic with > 90% at 0.56 kg ha−1. In the second year, a single application of 1.12 kg ha−1 triclopyr resulted in similar (P > 0.05) defoliation compared with two applications of 0.56 kg ha−1 triclopyr. After 1 yr, increasing triclopyr rate resulted in a linear increase in mortality. After 2 yr, two applications of triclopyr at 0.56 kg ha−1 and triclopyr + 2,4-D caused lower (P < .01) mortality (45%) than a single application of 1.12 kg ha−1 triclopyr (63%). Addition of 2,4-D to triclopyr did not increase mortality. After 2 yr, two applications of 0.28 kg ha−1 triclopyr resulted in 21% mortality while two applications of dicamba were ineffective. Defoliation was often greater with spring, compared with summer applications, but often depended on treatment and location. Mortality was greater (P < 0.01) at 1 and 2 yr after summer application compared with spring application at one location, but not the other. Roots of wax myrtle were sampled on 28-d intervals in the first year and analyzed for total non-structural carbohydrate (TNC). Starch composed 630 g kg−1 of TNC in myrtle roots, with highest concentration of TNC (120 g kg−1) in March and lowest (30 g kg−1) in August.

Absorption of 14C-imazaquin by leaves of field-grown flue-cured tobacco was similar when applied to young seedlings immediately after transplanting or to plants 3 wk after transplanting. The distribution of 14C in treated leaves indicated that 40% was absorbed, 54% remained in water extracts of leaf surfaces, and 6% was found in the epicuticular wax layer 8 d after treatment. Translocation of the herbicide from treated leaves to roots was very low (4 to 5%). In contrast, soil applications of imazaquin and subsequent uptake by roots resulted in retention of 40 to 53% in roots and translocation of 47 to 60% to shoots after 8 d. Analyses of methanol-soluble extracts of 14C indicated that more than 77% of the foliar-applied herbicide was metabolized in roots and upper shoots after 2 d. Similarly, 64% or more of the imazaquin was degraded in roots and shoots 2 d after root absorption.

Nicosulfuron (50 and 100 g ai ha−1), primisulfuron (40 and 80 g ai ha−1), imazethapyr (70 and 140 g ai ha-1), and DPX-PE350 (100 and 200 g ai ha-1) injury to corn, cotton, grain sorghum, rice, and soybean was evaluated at Fayetteville, AR, during 1989-90 and 1990-91. The crops were planted 0, 1, 2, 4, 8, 14 or 16, and 52 wk after herbicide application. Visible injury to all crops declined as the time interval increased. No visible injury was observed to any crop planted at least 14 wk after nicosulfuron or primisulfuron application, or 52 wk after DPX-PE350 application. Imazethapyr injured all crops except soybean at the 52-wk interval in 1990 but not in 1989.

Field experiments were conducted to determine carryover potential to grain sorghum and soybean of DPX-PE350 applied POST at 0.05, 0.1, and 0.2 kg ai ha−1 to cotton the previous year. DPX-PE350 did not injure soybean or affect yield adversely. Grain sorghum was injured and maturity delayed on a Sharkey silty clay but not on a Calloway silt loam. Grain sorghum yield was reduced on both soils 16 and 22%, respectively, by residues from the 0.1 and 0.2 kg ha−1 rates of DPX-PE350. In an incubation study, dissipation of DPX-PE350 was greater at 35 C than at 5 C., and did not differ between the two soils.

Cotton tolerance of DPX-PE350 applied POST alone, mixed with acephate, carbaryl, or dimethoate applied at 220, 1100, or 280 g ai ha−1, respectively, or following aldicarb, disulfoton, or phorate applied in the seed furrow at 1.0, kg ai ha−1 was evaluated. DPX-PE350 at 170 g ae ha−1 did not adversely affect seed cotton yield, fiber length, fiber length uniformity, or micronaire but did decrease fiber strength. The insecticides did not alter cotton response to DPX-PE350. Entireleaf morningglory was controlled 92, 95, and 96% with DPX-PE350 applied POST at 56, 110, and 170 g ha−1, respectively. Mixing acephate, carbaryl, or dimethoate with DPX-PE350 did not affect control.

During 1990, injury to tomatoes grown on the narrow land between the Albufera Lake (Spain) and the Mediterranean Sea was attributed to use of irrigation water coming from adjacent rice fields containing bensulfuron and quinclorac. A tomato root bioassay was developed to detect the herbicides in 10 ml of water. The assay was more sensitive to bensulfuron (0.5 ng ml−1) than quinclorac (100 ng ml−1). Only 30 ml of the affected water are necessary to conduct the test. Albufera water, sampled at three sites during 1991 and one during 1992 in the irrigation network canals caused different tomato main root length responses.

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.

Chlorsulfuron, thifensulfuron, bromoxynil, 2,4-D, glyphosate, and a combination of 2,4-D plus glyphosate were applied on newly planted and established ‘Lemberger’ wine grape at 1/3, 1/10, 1/33, and 1/100 of the maximum labelled rate in wheat or fallow to simulate exposure to drifted herbicides. All herbicides produced symptoms on grape but the most severe symptoms were with 2,4-D and the least severe with bromoxynil. Newly planted grape was more sensitive to herbicides than established grape. Although established grape recovered from injury caused by all treatments except 2,4-D and the highest rate of chlorsulfuron and glyphosate, newly planted grape recovered only from lower rates of bromoxynil. All herbicides resulted in diagnostic symptoms, but other symptoms were very similar to those caused by other stresses.

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.

Concern about the effects of pesticides on the environment and the desire to reduce purchased inputs are stimuli to reduce herbicide use. Field research was conducted at two locations for two growing seasons to identify integrated weed management practices in corn that are effective and economical. Weed control treatments included PRE application of a herbicide mixture of 1.8 kg ai ha−1 of atrazine plus 2.2 kg ai ha−1 of metolachlor alone, this mixture broadcast or band-applied at a reduced rate in combination with mechanical weeding, and mechanical weeding alone. Weed control, corn yield, and economic returns were generally higher in treatments combining herbicides and mechanical weeding than those using only mechanical measures. Without herbicides, timeliness of rotary hoeing was critical. Herbicide use can be reduced 50 to 75% in integrated systems with minimal risk of yield loss due to uncontrolled weeds.

Three field experiments were conducted in 1987 through 1989 to evaluate hogpotato control and rotational crop response resulting from applications of five herbicides. At the end of the first year, triclopyr and imazapyr controlled hogpotato late-season as high as 87 and 94%, respectively. Following a sequential application in 1988, triclopyr and imazapyr controlled 94 and 100% of hogpotato, respectively, during the 1989 growing season. Hogpotato biomass, collected at the termination of the experiments, was reduced by all treatments at all locations except at Altus where dicamba was applied in 1987 followed by a spot application of glyphosate in 1988. Soils from these experiments were bioassayed for residual herbicide activity using three potential rotational crop species. Tebuthiuron and imazapyr caused the greatest biomass reductions with cotton and wheat being the most sensitive species to these herbicides.

A study was conducted to evaluate efficacy of 17 PRE herbicides on seven weed species that are important competitors in container-grown ornamentals. Treatments included napropamide, metolachlor, acifluorfen, lactofen, oxyfluorfen, oryzalin, pendimethalin, prodiamine, trifluralin, isoxaben, oxadiazon, simazine and combination products. Control was evaluated by counting weed seedlings 42, 202, and 249 d after treatment. Some treatments provided nearly total control of less than 1.0 seedling per container at each rating over two years. Those treatments were: common groundsel—diphenyl ethers, isoxaben, oxadiazon, oxyfluorfen + oryzalin, and oxyfluorfen + pendimethalin; prostrate spurge—pendimethalin, prodiamine, prodiamine-ABD, trifluralin, oxadiazon, isoxaben + oryzalin, and methazole + prodiamine; common chickweed—isoxaben and isoxaben + oryzalin; hairy bittercress—oxyfluorfen, pendimethalin, prodiamine, prodiamine-ABE, oxadiazon, oxyfluorfen + oryzalin, oxyfluorfen + pendimethalin, and methazole + prodiamine; common ragweed—oxyfluorfen, prodiamine-ABD, methazole + prodiamine; Virginia pepperweed—lactofen, oxyfluorfen, oryzalin, pendimethalin, prodiamine, prodiamine-ABD, isoxaben, oxadiazon, oxyfluorfen + oryzalin, oryzalin + pendimethalin, isoxaben + oryzalin, and methazole + prodiamine; horseweed—oxyfluorfen, dinitroanilines, oxadiazon, oxyfluorfen + oryzalin, oxyfluorfen + pendimethalin, isoxaben + oryzalin, and methazole + prodiamine.

Experiments were conducted to compare rates and formulations of quinclorac for postemergent control of slender speedwell in cool-season turf. A 50% ae wettable powder formulation (50WP) was compared with two granular formulations, a 1% clay granule (1G) and a 0.4% corn cob granule (0.4G). Each formulation was applied at 0.3, 0.6, 0.8, and 1.1 kg ha−1. Additionally, 2,4-D at 1.1 kg ha−1 was applied alone and in combination with quinclorac 50WP at 0.8 kg ha−1. Slender speedwell control with the 50WP or 0.4G formulations was superior to that obtained with the 1G. At lower rates, slender speedwell control with the 50WP was greater than with the 0.4G; however, the rates required to obtain 95% control were not significantly different. Tank mixing quinclorac 50WP at 0.8 kg ha−1 with 2,4-D at 1.1 kg ha−1 did not improve slender speedwell control but increased roughstalk bluegrass injury. Kentucky bluegrass, perennial ryegrass, and tall fescue were not injured by quinclorac. Roughstalk bluegrass and chewings fescue were temporarily discolored. Turf injury was rate-related and more severe with the 50WP than the 1G formulation.

Asulam applied POST alone and in mixtures with residual herbicides and with DSMA and MSMA was evaluated for johnsongrass control. Johnsongrass control following treatment with asulam at 3.7 kg ai ha−1 was not improved by tank mixtures with the residual herbicides atrazine, metribuzin, pendimethalin, and terbacil compared with asulam applied alone. Johnsongrass injury symptoms appeared sooner when asulam was applied in mixtures with either DSMA or MSMA, but johnsongrass control 4 wk after treatment was similar to asulam applied alone. As a result of the johnsongrass control obtained with early POST treatments of asulam applied alone, cane and sugar yields were increased by 56 and 58%, respectively, when compared with the weedy check. Additional cane and sugar yield increases were not obtained by any of the asulam mixtures because johnsongrass control was not improved. Asulam applied again in May to johnsongrass regrowth improved late-season control in two of the three studies over a single early POST application, but cane and sugar yields were not increased.

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.

Experiments were conducted to evaluate selective herbicides for yellow and purple nutsedge control in nursery crops. Chlorimuron at 0.03 and 0.06 kg ai ha−1 suppressed yellow and purple nutsedge shoot growth either PRE or POST and did not reduce growth of barberry, Burford holly, Compacta holly, azalea, juniper, or photinia, although shoot tip chlorosis was noted in all species except Burford holly and juniper. Imazaquin at 0.25 and 0.5 kg ha−1 and imazethapyr at 0.06 and 0.21 kg ha−1 reduced growth of azalea. Imazethapyr also reduced growth of barberry, juniper, and photinia. Chlorimuron, imazaquin, and imazethapyr inhibited liriope and daylily growth. Pyridate applied at 1.0 and 2.0 kg ha−1 POST did not control purple nutsedge. Pyridate and flurtamone applied POST did not control yellow nutsedge as effectively as chlorimuron, imazaquin, or imazethapyr. Flurtamone at 0.5 and 1.0 kg ha−1 applied PRE or POST controlled purple nutsedge. Both pyridate and flurtamone visibly injured most nursery crops tested, although plants generally outgrew the damage.

An indirect enzyme-linked immunosorbent assay (ELISA) for EPTC was developed that may be useful for predicting enhanced carbamothioate herbicide degradation in adapted soils. A modified radioimmunoassay (RIA) procedure was used to detect antibodies specific for EPTC and establish antibody dilutions for optimum ELISA sensitivity. Antibodies were obtained from a rabbit injected with a butylate-analog protein conjugate. An indirect ELISA subsequently was developed for EPTC with a detection range of 10 to 1280 ng ml−1 in a 1:3 aqueous dilution of a 90:10 (v/v) acetonitrile (ACN):water soil extract. EPTC recovery from soil was > 96%, as determined by conventional gas chromatography. Measurement of low concentrations of residual EPTC with the ELISA was less quantitative than by gas chromatography, but the immunoassay provided a rapid, potentially cost-effective method for screening soils to determine enhanced carbamothioate degradation.

In 1987-89, field experiments were conducted to evaluate rates of activated carbon in transplant water to reduce injury to tobacco from imazaquin. Rates of activated carbon were 0, 2.2, 4.5, and 9 kg ha−1 in 1987 and 0, 9, 18, and 36 kg ha−1 in 1988-89. Imazaquin rates were 0, 0.3, and 0.6 kg ha−1 applied over-the-top immediately after transplanting. Results indicated that 9 kg ha−1 of activated carbon was the minimum amount to reduce injury from imazaquin. No additional protection was achieved with rates above 9 kg ha−1, whereas lower rates appeared to offer less protection based on visible stunting ratings.