Spring-applied herbicides were evaluated in the field in 1982 through 1984 in western Nebraska for selective weed control in irrigated seedling alfalfa (Medicago sativa L. ‘Appollo’). Weed densities were least in plots treated preplant with benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] in combination with postemergence applications of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. Combinations of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and fluazifop-butyl {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} with bromoxynil provided less grass control than sethoxydim or fluazifop-butyl applied alone. Annual weeds did not reduce alfalfa stand density.

The soil activity of foliar-applied HOE 29152 {2-[4-trifluoromethyl-phenoxy)phenoxy] propanoic acid} and diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} on barnyardgrass [Echinochloa crus-galli (L.) Beauv.] and yellow foxtail [Setaria lutescens (Weigel) Hubb.] was evaluated in the greenhouse. HOE 29152 was applied at 0.1, 1.2, 2.4, and 3.5 kg/ha; and diclofop was applied at 0.5, 2.7, 4.9, and 7.2 kg/ha. Both compounds applied to roots or shoots before emergence reduced growth. Neither compound had much, if any, effect on the germination of barnyardgrass or yellow foxtail; however, the survival of both weed species that germinated in solutions of these two compounds was reduced. The number of seedlings surviving for both weed species was reduced by both compounds. Seedling survival from germination imbibition by diclofop and HOE 29152 was influenced by the presence of light at the time of seed germination.

A 3-yr study was conducted to evaluate efficacy and soybean tolerance of cinmethylin. Cinmethylin was applied preemergence alone at 0.6, 0.8, and 1.0 kg ai/ha or in combination with metribuzin at 0.3 kg/ha. These treatments did not injure soybeans in field trials in 1984, 1985, and 1986. The combination of cinmethylin at 0.7 kg/ha and metribuzin at 0.3 kg/ha controlled more than 90% of large crabgrass, fall panicum, and yellow foxtail. Redroot pigweed and common lambsquarters control was also excellent. Residual control of all grass species was excellent for 8 weeks after preemergence application, followed by reduced control in two of the three grasses. The combination of cinmethylin and metribuzin at 0.7 and 0.3 kg/ha, respectively, significantly increased soybean yields compared to those of untreated plots. These yields were comparable with those obtained from the combination of alachlor and metribuzin at 2.0 and 0.3 kg/ha, respectively. Cinmethylin treatments had no adverse effects on soybean yield components including pods/plant, seed/pod, and seed weight. Cinmethylin shows potential as a preemergence herbicide for full-season weed control in soybean production.

The antagonism of the methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy propanoic acid} by bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] was evaluated through studies of absorption and translocation in yellow foxtail [Setaria lutescens (Weig. ex Stuntz.) Hubb. # SETLU]. Leaf penetration of haloxyfop was reduced 37% in the presence of bentazon. Bentazon had no effect on translocation from the treated leaf. Direct chemical interactions and contact activity by bentazon do not account for the reduced uptake of haloxyfop. Experimental evidence shows the benzothiadiazione structural class of chemistry to be general antagonists of absorption for foliarly applied herbicides.