Spring small grains were not as competitive with barnyardgrass and witchgrass as winter wheat. Winter wheat grain yields were greater than spring barley or spring wheat in 1986, 1987, and 1988 and oat in 1986 and 1988. Barnyardgrass, stinkgrass, and witchgrass control with glyphosate plus 2,4-D plus atrazine at 0.6 plus 0.8 plus 1.7 kg ha−1 was usually less when the herbicides were applied to stubble of spring small grain versus winter wheat due to the advanced weed growth at treatment Barnyardgrass and witchgrass were more difficult to control than stinkgrass, redroot pigweed, tumble pigweed, kochia, and tumble thistle. No-till corn planted into winter wheat stubble had fewer barnyardgrass and witchgrass than corn planted into spring wheat stubble. The addition of metolachlor plus atrazine at 1.7 plus 0.6 kg ha−1 eliminated differences among small grain cultivars in weed control in corn. Corn grain yields from winter wheat plots were greater than other small grains in 1989 because of better weed control and more crop residue.

Laboratory studies were conducted to determine the effect of rainfall timing and antecedent moisture on atrazine leaching through intact soil cores taken from no-till and conventional-till corn fields. Simulated rainfall was applied to no-till and conventional-till cores 1 to 14 d after atrazine application and, in a second study, one d after atrazine was applied to no-till and conventional-till cores at 1 to 800 kPa soil moisture. Increasing the lag time between atrazine application and rainfall from one to 14 d reduced the amount of atrazine leached by about 50% for both no-till and conventional-till soil cores. During the same time period, the amount of atrazine adsorbed to soil increased by about 30% for both tillages. Soil dryness (antecedent moisture) at the time of atrazine application had no effect on the amount of atrazine leached through conventional-till cores. However, leaching decreased in no-till cores as antecedent moisture decreased from 1 to 33 kPa; drying to 800 kPa had no further effect. The leaching rate of atrazine was much higher for the initial 0.5 pore volume than for the next 1.5 pore volume at all rainfall timing and antecedent moisture levels. This behavior is indicative of preferential transport.

Efficacy, movement, and degradation of dithiopyr and pendimethalin were monitored after application to perennial ryegrass turf in 1990 and 1991. Dithiopyr at 0.6 kg ai ha−1 reduced large crabgrass infestation by ≥ 90% up to 87 DAT in both years, while pendimethalin at 1.7 kg ai ha−1 provided similar control up to 59 DAT in 1 of 2 yr. Turf thinning due to disease and insect damage in 1990 allowed more herbicide to reach the thatch, mat, and underlying soil in 1991. In both years, more pendimethalin but less dithiopyr was found in thatch 7 DAT than 1 DAT, suggesting greater pendimethalin retention in verdure and thatch. Precipitation was greater after herbicide application in the second year, and concentration in the mat layer reached a maximum by 7 DAT compared to 14 DAT in 1990. Maximum concentrations of dithiopyr and pendimethalin in soil at 0 to 5 cm deep were 20 and 56 μg kg−1, respectively, measured 7 DAT in 1991. Herbicide concentration 5 to 10 cm deep was ≤ 5 μg kg−1 at all sampling dates in 1990. In 1991, dithiopyr and pendimethalin concentrations 5 to 10 cm deep did not exceed 4 and 20 μg kg−1, respectively, measured within 1 DAT. Neither herbicide was detected 10 to 20 cm deep, nor in samples collected 30 cm outside of the experimental plots in either year. At 126 DAT (final sampling date), little herbicide was detected in verdure, but residues were found in most thatch and all mat samples. The estimated time for a 50% reduction in detectable residues (DT50) of dithiopyr and pendimethalin from the sampling zone was 35 and 23 days, respectively.

Field experiments were conducted in 1992 and 1993 to determine the timing and amount of rainfall required to activate UCC-C4243 applied preemergence. UCC-C4243 at 0, 70, and 140 g ai ha−1 was applied 1, 7, 14, and 21 d before 0.5 or 2 cm of simulated rainfall. Temporary rainshelters protected field plots from natural rainfall during the 21 d dry period. Herbicide activity was determined in the field by seeding lentil, wheat, common lambsquarters, and field pennycress and in the greenhouse by a sugarbeet bioassay of soil samples (0 to 3 cm depth) taken from all plots immediately before irrigation. UCC-C4243 did not injure wheat; however, lentil population was reduced when simulated rainfall occurred within 7 d after application. Lentil injury was greater with higher herbicide rate and higher water level. UCC-C4243 at 70 and 140 g ha−1 reduced populations of both weed species by 75 and 90%, respectively, when either 0.5 or 2 cm simulated rainfall was received within 1 d after herbicide application. Weed control was reduced with a 21 d delay between herbicide application and water activation. The sugarbeet bioassay showed a linear decrease of herbicide activity over time and also with accumulated photosynthetically active radiation. After 17.9 d, herbicide activity on a dry soil surface decreased 50%. Laboratory investigations show that [14C]-UCC-C4243 on glass slides was photodegraded by near ultraviolet light (290 to 400 nm). Volatilization of 14C-labeled herbicide from glass slides was less than 5% after exposure to turbulent air for 48 h.

Broom snakeweed, a perennial rangeland shrub, is highly variable morphologically and can grow under a broad range of environmental conditions. In this study, isozyme analysis using starch gel electrophoresis was used to quantify genetic variability within and among New Mexico populations of broom snakeweed. Eight separate populations of broom snakeweed and one population of threadleaf snakeweed as a comparison were investigated. of the 10 enzyme systems examined, 16 loci were identified in eight populations and two species. Eleven loci were monomorphic in eight populations and two species and five loci were polymorphic in at least one population or species. Genetic variability was large in broom and threadleaf snakeweed populations as determined by isozyme analysis. Genetic variability among broom snakeweed populations was greater than that within populations for the five polymorphic loci. Cluster analysis of genetic distance and identity for the eight populations and two species characterized two major groups. Within broom snakeweed, cluster analysis characterized five groups. The two species shared most common alleles. The genetic variation identified in this research may account for the morphological differences and broad geographical distribution of broom snakeweed.