Laboratory experiments were conducted to evaluate the biodegradation of 14C-labeled butylate, cycloate, EPTC, pebulate, and vernolate in three butylate-history soils that had received three to eight applications of butylate under field conditions. After 20 days, biodegradation of butylate and EPTC was accelerated and had no lag phase in all three butylate-history soils. Butylate-adapted microorganisms were cross-adapted for EPTC and degraded EPTC as readily as butylate. Biodegradation of butylate and EPTC in Dothan soil without a butylate history exhibited a lag phase of 6 days after which 14CO2 was evolved at an exponential rate. This indicated that enhanced biodegradation was induced after one application of butylate or EPTC. Butylate-adapted microorganisms were cross-adapted for vernolate and pebulate in Dothan and pebulate in Wagram soils with a butylate history. Biodegradation of vernolate and pebulate was not enhanced in Varina butylate-history soil. After 20 days, there was no cross-adaptation for cycloate in any soil. These findings indicated that biodegradation of carbamothioates was influenced by soil type and previous carbamothioate use and that caution should be exercised in use of EPTC on fields of previous butylate use.

Two-level fractional factorial design experiments were conducted in growth chambers to determine the influence of environmental factors and adjuvants on the foliar penetration of the sodium salt of acifluorfen in velvetleaf. Relative humidity (RH) was found to have the greatest effect on penetration. Temperature was the second most important factor. Although soil moisture significantly affected penetration, this effect was much less than that produced by RH and temperature. Diammonium phosphate (DAP) was the most effective adjuvant tested. The use of DAP at 1.12 kg/ha significantly increased penetration. The effect of DAP was less than either RH or temperature. Oxysorbic (5 POE) surfactant also significantly increased penetration. Glycerol and oxtoxynol (7 to 8 POE) surfactant had no effect on penetration. In separate experiments, acifluorfen penetration at low and high RH and with the addition of DAP was measured to verify these results. Acifluorfen penetration into velvetleaf increased approximately ninefold with changes in RH from low to high. Penetration increased sevenfold when DAP was added. DAP was by far the most effective adjuvant increasing acifluorfen penetration into velvetleaf under conditions of low RH. Oxysorbic (5 POE) surfactant slightly increased penetration under these conditions.

Two leaf-spotting pathogens, [Bipolaris setariae (Saw.)] and [Piricularia grisea (Cke.) Sacc.], were isolated from severely infected goosegrass plants. Pathogenicity tests conducted at 28 C showed that both fungi were 100% effective in infecting goosegrass when given a 72-h dew period. Dew period temperature and duration requirements were tested by inoculating 2-week-old plants with conidial suspensions of each fungus and incubating them in dew chambers (100% relative humidity). Disease index increased as dew period duration increased for both fungi and at all temperatures tested. Infection occurred at all temperatures with an optimum of 24 to 28 C for B. setariae and 28 C for P. grisea. In host range tests, representative plants of the Fabaceae, Malvaceae, Poaceae, and Solanaceae were inoculated with suspensions of either 20 000 or 60 000 spores/ml of each fungus and placed in growth chambers at 28 C. Infection was limited to members of the Poaceae. Sorghum showed a hypersensitive response to B. setariae. Both cultivars of corn developed light symptoms in response to both fungi at 20 000 and 60 000 spores/ml.

Soybean field experiments were conducted to compare weed interference data obtained from small 2.7-m2 plots to that obtained from large 11-m2 plots. Soybean row spacings of 15, 30, 45, and 90 cm were used. Sicklepod, common cocklebur, and soybean biomass as dry matter were harvested from small plots 10 weeks after planting and were compared to weed biomass and soybean seed yield from the large plots. Sicklepod and common cocklebur biomass in small plots increased and soybean biomass decreased as soybean row spacing increased. Soybean biomass was not affected by row spacing when weeds were not present. Sicklepod and common cocklebur biomass in large plots increased and soybean seed yield decreased as soybean row spacing increased. Soybean seed yield was not affected by row spacing when weeds were not present. Comparison of regression coefficients for paired regression lines indicates that soybean biomass from small plots may be substituted for seed yield from large plots as a measure of sicklepod or common cocklebur interference if both size plots use the same soybean row spacing and are irrigated until harvest.

The impact of four weed management systems on weed seed reserves in soil, yearly weed problem, and production of barley, corn, pinto bean, and sugarbeet was assessed where these crops were grown in rotation for 4 consecutive years in four cropping sequences. Weeds were controlled in each crop with only conventional tillage or conventional tillage plus minimum, moderate (system 1), and intensive (system 2) levels of herbicides. Seed of annual weeds from 11 genera were identified, with barnyardgrass and redroot pigweed comprising 66 and 19%, respectively, of the initial 90 million weed seed/ha present in the upper 25 cm of the soil profile. After the fourth cropping year, overall decline in total number of weed seed in soil was 53% when averaged over four cropping sequences and four weed management systems. Over the 4-yr period, about 10 times more weeds escaped control in system 1 than in system 2; and within a crop, the fewest number of weeds escaped control annually in barley. System 2 had the highest herbicide use in each cropping sequence, the fewest weeds at harvest, and the smallest adjusted gross return over the 4-yr period in three of four cropping sequences.

An economic analysis of four weed management systems employed on four crop sequences in a barley-corn-pinto bean-sugarbeet rotation in eastern Colorado was computed. Weeds were controlled in each crop with only conventional tillage or conventional tillage plus minimum levels of herbicides (systems 3 and 4), moderate levels of herbicides (system 1), or intensive levels of herbicides (system 2). Adjusted gross returns were higher for systems 3 and 4 where herbicide use was less/year and decreased over 4 yr than for systems 1 and 2 where herbicide use was higher/year and constant. When the four crop sequences were aggregated using yield and sucrose indices, the least herbicide-intensive weed management system had $440/ha/4 yr higher indexed adjusted gross return than the most herbicide-intensive weed management system. An income risk analysis showed that the herbicide-intensive weed management system was not risk efficient and that producers would select one of the other three less herbicide-intensive weed management systems depending upon their risk preferences.