The influence of fall (late September or late October)-applied dicamba (3,6-dichloro-2-methoxybenzoic acid) on spring-planted soybean [Glycine max (L.) Merr.] and sunflower (Helianthus annuus L.) was studied at five sites in Minnesota during 1983 and 1984. At the two southern Minnesota locations, only late-October applications of dicamba at the highest rate (4.5 kg ae/ha) reduced yields of spring-planted soybean and sunflower. At the central and the two northern Minnesota locations, both late-September and late-October applications of dicamba at 1.1 kg/ha and higher caused injury and yield reductions to soybean and sunflower planted the following year. The two southern Minnesota locations had generally higher levels of precipitation, higher temperatures, higher organic matter soils, and lower pH levels compared to the central and northern Minnesota locations. These climatic and soil characteristics reduced dicamba persistence at the two southern Minnesota locations.

Efficacy of soil and/or foliage applications of the sodium salt of chloramben (3-amino-2,5-dichlorobenzoic acid) was compared, and the influence of growth stage and oil base within adjuvants on chloramben efficacy was evaluated on velvetleaf (Abutilon theophrasti Medic. # ABUTH). In greenhouse experiments, soil applications reduced growth of velvetleaf treated at the six- to seven-leaf stage (15-cm height) more than did foliage applications. Simulated rainfall applied 48 h after chloramben was applied to foliage significantly increased chloramben activity. Chloramben plus an oil concentrate applied at 3.4 kg ae/ha plus 2.3 L/ha reduced fresh and dry weight less as growth stage advanced in both greenhouse and field experiments. Origin of oil present in the oil concentrate did not influence the activity of chloramben plus oil concentrate in either the greenhouse or in the field. Chloramben plus oil concentrate reduced seed capsule (boll) production 70% or more in velvetleaf plants treated at each of three growth stages in one year and reduced capsule production 90, 90, and 28% in plants treated at early vegetative, late vegetative, and flowering stages, respectively, in the second year. Viability of seed was less from plants treated at a vegetative stage compared to the flowering stage.

Mobility and sorption of radiolabeled sulfometuron {2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino] carbonyl] amino] sulfonyl] benzoic acid} and imazapyr {(±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-pyridinecarboxylic acid} were evaluated in five soils representative of the major soil types in Alabama. Thin-layer soil chromatography indicated that sulfometuron was slightly more mobile (average Rf = 0.86) than imazapyr (average Rf = 0.79). Sulfometuron was more subject to sorption (average kd = 0.29) than imazapyr (average kd = 0.09) in batch equilibrium experiments. Least sorption of both herbicides occurred on clay soils, and maximum sorption occurred on a sandy clay. Similar results were obtained with a soil solution recovery technique. Sorption of both herbicides was exhanced by temporary reduction in soil water content and by lowering soil pH. The pH response of imazapyr was greater than that of sulfometuron.

Microbial degradation of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} was monitored by measuring 14CO2 evolution for 7 months under controlled laboratory conditions. Up to 10% of the 14C chain-labeled imazaquin that was applied to a Crowley silt loam was evolved as 14CO2 in 7 months. Less evolution of 14CO2 occurred on a Sharkey silty clay, a soil with higher clay and organic matter content, than on silt loam soils. The loss of 66 to 100% of the imazaquin applied to a Crowley silt loam incubated for 8 months at 18 C or 35 C, respectively, suggested that metabolic changes in addition to CO2 evolution were occurring. Rapid loss of imazaquin phytotoxicity occurred when soils were held at warm-moist (35 C and −33 kPa) conditions conducive to microbial growth. Imazaquin was more persistent in soils stored under cool, dry (18 C and −100 kPa) conditions. Imazaquin on a soil surface dissipated rapidly when exposed to ultraviolet light or sunlight. Photodecomposition could be a major mode of imazaquin dissipation if this herbicide is allowed to remain on the soil surface.