Field studies were conducted from 1991 through 1993 to determine the effects of stale seedbed management practices on weed control in peanut. Main plots were four levels of stale seedbed management: deep till (23 cm) and plant the same day (standard system), deep till 6 wk early and shallow till (7.6 cm) at 2 wk intervals prior to planting, deep till 6 wk early and application of glyphosate (1.1 kg ai ha−1) 1 wk prior to planting, and deep till 6 wk early without additional treatment prior to planting. Sub-plots were three levels of weed management following peanut planting; intensive, basic, and cultivation alone. Stale seedbed management practices stimulated weed emergence when followed by other control measures prior to planting. Populations of Florida beggarweed, Texas panicum, and yellow nutsedge were lower when stale seedbeds were shallow tilled at 2 wk intervals prior to planting, resulting in greater peanut yields. Weeds on nontreated stale seedbeds were difficult to control once peanut was planted and reduced yields. Stale seedbed management practices generally had no effect on the quantity of foreign material contaminants originating from weeds, soil, or peanut plant in harvested peanut. These results indicate that shallow tillage on stale seedbeds can reduce weed populations prior to planting and increase peanut yields.

Short term incubations (4 d) were conducted to assess the effect of a wetting/drying cycle on atrazine sorption, as well as biodegradation, as a function of various atrazine concentrations (ca. 5, 10, and 25 μg g−1 soil) and levels of added crop residues (0, 5, and 10% cornstalks by weight), using a technique that allowed independent analysis of soluble and sorbed atrazine. Soil solution atrazine concentrations decreased, and KdS increased with increasing crop residues. The sorptive capacity of cornstalks for atrazine was estimated to be 860 μg g−1 vs 28 μg g−1 for unamended soil. Drying and rewetting resulted in lower soil solution concentrations and decreased extraction efficiencies (13 to 22%) for sorbed atrazine; the effect was most pronounced with added cornstalks. High recoveries of 14C from soils (combustion data) indicated that atrazine was not lost to volatilization. Rapid rates of biodegradation were observed in cornstalkamended soils shortly after rewetting; degradation was not observed in unamended soil. A longer incubation (6 wk) was conducted with ca. 10 μg g−1 atrazine and 5% cornstalks to assess metabolites and kinetics of biodegradation. Atrazine disappearance was observed after ca. 2 wk with concomitant production of deethyl- and deisopropyl-atrazine at a ratio of ca. 2:1. Dealkylated-atrazine accumulated after ca. 3 wk; there was no evidence for hydroxy-atrazine production. These data suggest that biodegradation may play an important role in atrazine losses in the field despite wetting/drying cycles. In addition, there may be apparent losses of atrazine due to decreased extraction efficiencies as a consequence of wetting/drying cycles, resulting in underestimation of field residues.

Greenhouse and laboratory experiments were conducted to determine the effect of soil organic matter on the synergistic interaction between nicosulfuron, a sulfonylurea herbicide, and the insecticide terbufos in corn. Terbufos was applied infurrow at planting to soils containing 1, 3, and 5% organic matter and nicosulfuron was applied POST to corn at the three-leaf growth stage. The combination of terbufos and nicosulfuron reduced corn fresh weight 75, 45, and 41 % in soils containing 1, 3, and 5% organic matter, respectively. Terbufos increased [14C]nicosulfuron uptake into corn grown in both 1 and 5% organic matter soils. Terbufos decreased epicuticular leaf wax deposition on corn leaves by 35 and 18% in 1 and 5% organic matter soils, respectively. [14C]Nicosulfuron was completely metabolized after 24 h in the absence of terbufos. In the presence of terbufos, 19 and 11% of intact [14C]nicosulfuron remained 24 h after treatment while 11 and 6% remained after 48 h in the 1 and 5% organic matter soils, respectively. In vivo acetolactate synthase activity was reduced to 3 and 20% of control by nicosulfuron at 24 h and to 6 and 38% of control at 48 h, respectively, in the 1 and 5% organic matter soils that contained terbufos. These experiments indicated that soil organic matter is an important factor in determining the level of injury expected from the synergistic interaction between nicosulfuron and terbufos in corn.

A water-corn oil (unrefined) emulsion has promise as a carrier for application of the mycoherbicide, Colletotrichum truncatum. We investigated this formulation (normal emulsion; oil in water) for influences on conidia germination, appressoria formation, and mycoherbicidal activity of C. truncatum. Germination of conidia after application to hemp sesbania leaves was increased from 30% in water alone to 92% in the water-corn oil emulsion (water:oil, 1:1, by vol). The emulsion did not affect appressoria formation. of the several other oils tested, safflower seed oil enhanced in vitro germination but did not enhance germination and mycoherbicide activity when the conidia-emulsion formulation was applied to hemp sesbania leaves. Application of C. truncatum conidia in the unrefined corn oil emulsion to hemp sesbania seedlings resulted in 89 to 97% control of the weed after a 24 to 72 h dew delay. The emulsion enhanced mycoherbicide efficacy by stimulating conidia germination by protecting the conidia during a dew-free period, hence, increasing weed infection when a dew occurred.

A reduced-till (RT) experiment determined the effect of rye seeding density and method of kill on rye biomass persistence, weed suppression, and tomato yield. ‘Wheeler’ rye was seeded at 56, 110, and 170 kg ha−1 in the fall of 1988 and 1989 in Champaign, IL; Lexington, KY; and Lafayette, IN. One wk before transplanting tomatoes, rye was desiccated either by applying glyphosate at 1.1 kg ha−1 and mowing (RT-glyphosate) or by mowing alone (RT-mowed). Both methods left rye residues on the soil surface as a mulch. Seeding density did not affect rye biomass, weed control, or tomato yield. Rye biomass differed depending on location and year, ranging from 320 to 1150 gm−2. Rye was completely killed by glyphosate, but regrew following mowing. RT-glyphosate suppressed weeds for 4 to 8 wk, which was similar to the suppression from conventional tillage (fall plowing with spring disking and harrowing) with trifluralin and metribuzin (CT-herbicide). Weed communities varied, but redroot pigweed and giant foxtail were present at all three locations. All treatments required supplemental weed management for commercially acceptable control. Except for IL in 1990, processing tomato yields (kg ha−1) in RT-glyphosate with hand-weeding were equal or better than yields in the CT treatments.