The impact of POST applications of fluazifop-P on sugarcane grown in Louisiana was determined for 3, 6,11, 22, and 44% of the lowest rate recommended for the control of johnsongrass in soybean (100 g ai ha−1). In field studies, sugarcane injury 4 WAT increased as the rate of fluazifop-P increased. Injury in excess of 80% was observed when fluazifop-P at 44 g ha−1 was applied in May and June and 54% when applied in August Sugarcane stalks treated with fluazifop-P were fewer in number, shorter and lighter, and immature at harvest This resulted in lower Brix and sucrose levels, higher fiber content, and ultimately lower sugar yields. Reductions in sugar yields associated with an application of fluazifop-P closely paralleled visual injury 4 WAT. Injury from application of fluazifop-P was also evident in the subsequent ratoon crop where reductions in spring shoot counts of 14 to 25% were obtained even when fluazifop-P had been applied at 6 g ha−1 the previous year. Greenhouse studies indicated that the response observed in the field with CP 70-321 sugarcane was indicative of the major cultivars grown, with the possible exception of CP 74-383.

Barnyardgrass is a problem in winter wheat fields in the central Great Plains following harvest. Glyphosate plus 2,4-D efficacy on barnyardgrass with or without atrazine was investigated under various watering events at three sites in west central Nebraska. Two experiments were initiated at each site. One experiment dealt with rainfall and the other rainfall plus irrigation. Main plots in stubble fields infested with barnyardgrass were sprayed with glyphosate plus 2,4-D at 0.4 plus 0.7, 0.5 plus 0.8, and 0.6 plus 1.0 kg ae ha−1 alone and with 2.2 kg ai ha−1 atrazine. Barnyardgrass was under drought stress in unwatered areas in 1991 at two sites, but the 1993 site was waterlogged. Glyphosate plus 2,4-D at 0.6 plus 1.0 kg ha1 controlled 62, 99, and 100% of the barnyardgrass at the three sites 30 DAT. Nevertheless, control was reduced to 48, 88, and 35% when atrazine was combined with glyphosate plus 2,4-D. Poorest control came when plants were under stress from drought or waterlogging and atrazine was included in the spray solution. In subplots barnyardgrass plants in a 0.8 m2 area were watered 6, 3, or 1 d before spraying and 1, 4, 7, or 11 d after spraying. By watering drought-stressed barnyardgrass 6 d before spraying, control generally was similar or better than with later watering dates. Watering 6 d before spraying with glyphosate plus 2,4-D plus atrazine at 0.6 plus 1.0 plus 2.2 kg ha−1 reduced but did not eliminate antagonism from atrazine.

Granules of isoxaben plus trifluralin and liquid applications of isoxaben plus oryzalin were applied to miniature nursery plots covered with plastic, woven landscape fabric, or gravel with no cover. Herbicide concentrations were monitored in runoff water over a 30 d period. Runoff losses of isoxaben from the sprayable formulation applied to gravel were 5% greater than from plastic and 4% greater than losses from fabric in 1992. Similarly, oryzalin losses from the sprayable formulation applied to gravel were 7% greater than losses from plastic and 4% greater than losses from the fabric ground cover. In contrast, loss of isoxaben from the granular formulation applied to plastic was 7% greater than loss from gravel in 1993. Isoxaben losses from the granular formulation applied to fabric were intermediate. Trifluralin losses from the granular formulation applied to plastic and fabric were both 3% greater than losses from gravel. In addition, isoxaben losses from the granular formulation were 11 and 10% greater than loss from the sprayable formulation applied to the plastic and fabric-covered plots, respectively. Isoxaben losses from the sprayable formulation applied to gravel were 11% greater than losses from the granular formulation. In an experiment to determine herbicide release patterns and the effect of light on residues from the granular formulation of isoxaben and trifluralin in irrigation effluent, water was monitored for 36 d. Approximately 20% of the applied isoxaben and 7% of the applied trifluralin was detected in irrigation water during the 36 d period. These studies indicate that runoff losses and the ultimate fate of isoxaben, oryzalin, and trifluralin applied in nursery settings depend on factors including ground cover composition, herbicide formulation, and photochemical degradation.

Laboratory studies were conducted to determine the relative sorption, mobility, and degradation rates of triclopyr and 2,4-D on two surface soils and two subsoils from the rice-producing areas of Arkansas. Triclopyr sorption was slightly greater than 2,4-D sorption. However, mobility of the herbicides on a given soil did not differ. Sorption of both herbicides was greatest and mobility lowest on a subsoil with the lowest pH. Triclopyr degradation rates were lower than 2,4-D degradation rates in a dark incubator. The average half life was 138 d for triclopyr and 21 d for 2,4-D. High soil moisture content (0 versus 100 kPa water tension) increased the rate of 2,4-D degradation. Triclopyr degraded more rapidly at 30 C than at 15 C. The dissipation rates of both herbicides were lowest on the soil on which sorption was greatest.

Current and projected increases in the concentrations of CO2 and other radiatively-active gases in the Earth's atmosphere lead to concern over possible impacts on agricultural pests. All pests would be affected by the global warming and consequent changes in precipitation, wind patterns, and frequencies of extreme weather events which may accompany the “greenhouse effect.” However, only weeds are likely to respond directly to the increasing CO2 concentration. Higher CO2 will stimulate photosynthesis and growth in C3 weeds and reduce stomatal aperture and increase water use efficiency in both C3 and C4 weeds. Respiration, and photosynthate composition, concentration, and translocation may be affected. Perennial weeds may become more difficult to control, if increased photosynthesis stimulates greater production of rhizomes and other storage organs. Changes in leaf surface characteristics and excess starch accumulation in the leaves of C3 weeds may interfere with herbicidal control. Global warming and other climatic changes will affect the growth, phenology, and geographical distribution of weeds. Aggressive species of tropical and subtropical origins, currently restricted to the southern U.S., may expand northward. Any direct or indirect consequences of the CO2 increase that differentially affect the growth or fitness of weeds and crops will alter weed-crop competitive interactions, sometimes to the detriment of the crop and sometimes to its benefit.