Research on the timing of herbicide application on no-till sorghum [Sorghum bicolor (L.) Moench.] planted into undisturbed winter wheat (Triticum aestivum L.) stubble was conducted at North Platte, NE, during 1980–1982. Applying some herbicides 41 and 25 days prior to planting sorghum maintained weed control, reduced sorghum injury, and increased sorghum yields when compared to application at planting. It was necessary to apply cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile} at 2.7 kg ai/ha 41 days prior to planting to avoid sorghum injury. Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] + 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 2.2 + 0.3 kg/ha reduced grass yields 97, 98, and 99%, while reduction with alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] + 2,4-D at 2.8 + 0.3 kg/ha was 93, 41, and 63%, respectively, when herbicides were applied 0, 25, and 41 days prior to planting.

Absorption and translocation of 14C-dicamba (3,6-dichloro-o-anisic acid) in seven salt formulations were determined 60 h after application to leaves of soybean [Glycine max (L.) Merr. ‘Williams’] grown in nutrient solution. The dimethylamine (DMA) formulation was consistently absorbed and retained in the plant in amounts equal to or greater (46% of recovered 14C) than other formulations (which averaged 19% of recovered 14C) when applied without surfactant. Absorption and subsequent retention of the DMA formulation in the plant was least affected of all formulations by the addition of a surfactant. With a surfactant, absorption of the DMA, monoethanolamine (MEA), and inorganic salt formulations was similar (>75% of recovered 14C). Addition of seven surfactants to the K-salt of dicamba increased both the amount of 14C absorbed by 35 to 56% and the amount recovered in the plant. All surfactants except one enhanced absorption of the K-salt of dicamba to a similar degree. Dicamba exhibited predominantly symplastic translocation with the majority of 14C being recovered in the new second trifoliolate leaves and nutrient solution. As much as 66% of the radioactivity absorbed through the leaves was exuded by roots into the nutrient solution 60 h after leaf treatment.

The acetanilide herbicides alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], the ethyl ester of diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl)glycine], or H-26910, the isopropyl ester of N-(chloroacetyl)-N-(2-methyl-6-ethylphenyl)glycine, failed to inhibit yellow nutsedge (Cyperus esculentus L. ♯ CYPES) tuber sprouting in petri dishes. At 3.5 and 0.35 μM, all herbicides inhibited growth of newly emerging shoots. There was no significant difference in activity among alachlor, metolachlor, diethatyl ethyl, and R-26910 on yellow nutsedge sprouts grown in petri dishes. In soil, metolachlor and alachlor were equally effective for yellow nutsedge control. Both were more effective than H-26910 at high levels of soil organic matter. Diethatyl ethyl was least effective at all levels of soil organic matter. For all herbicides evaluated, activity decreased with increased levels of organic matter in the soil. For acetanilide herbicides to be effective on yellow nutsedge, they needed to be in the soil zone, above or at the level of the tuber.

A 4.6-m-long, segmented, flexible-pipe ropewick applicator was constructed to apply picloram (4-amino-3,5,6-trichloropicolinic acid) to leafy spurge (Euphorbia esula L. ♯ EPHES) and other weed species. Gauge wheels on each ropewick applicator segment permit height adjustments, and a loose, independent, vertical flexing action permits the segments to effectively traverse depressed or raised areas. The applicator was designed for use in pastures with rough, uneven terrain where it is difficult to uniformly wipe herbicide solution on plants with a rigid-pipe ropewick. The applicator was found to be durable and effective in applying picloram to leafy spurge.

Field studies were conducted in 1981 to 1983 to evaluate selected herbicides for control of a natural infestation of woolly croton (Croton capitatus Michx. ♯ CVNCP) in soybean [Glycine max (L.) Merr.]. Ineffective woolly croton control was obtained with all preemergence herbicides evaluated. Early postemergence treatments of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and lactofen {1-(carboethoxy)ethyl) 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate} provided excellent woolly croton control. Postdirected applications of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] applied at the V4 stage of soybean growth and tank mixes of cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea], or metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] plus 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] applied at the V4 and repeated at the V6 stage of soybean growth also provided effective control.

The sweet potato [Ipomoea batatas (L.) Lam.] cultivars ‘Jewel’, ‘Centennial’, ‘Caromex’, and breeding lines ‘W-70’, ‘W-152’, and ‘Tinian’ (PI 153655) were evaluated for metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as–triazin5(4H)-one] tolerance in greenhouse and field studies. Tinian was the most tolerant line. Its yields were not reduced by 2.2 kg/ha metribuzin in the field. Jewel, Centennial and W-152 were intermediate in response to metribuzin, and W-70 and Caromex were most susceptible. Regression analyses indicated a high correlation between the response of sweet potato cultivars to 0.5 ppm metribuzin incorporated in a potting mix in the greenhouse and their response to 1.1 kg/ha metribuzin applied after transplanting in the field.

The importance of including crop density in studies of weed-wheat competition and in making estimates of crop losses due to weeds was demonstrated. Wheat density in adjacent quadrats of 1 m2 varied by an average of 25 plants in the farm fields and research plots examined. Differences between adjacent quadrats were in the same range for fields sown with different implements. Yield per plant, dry weight per plant, and tillering per plant decreased with increasing wheat density. For weed-crop competition studies in small-grain crops, the yields of weed-free and weedy quadrats are normally compared to estimate crop loss caused by competition. It was demonstrated that such estimates can be highly distorted if crop density is not taken into account. Current procedures used widely in agronomic competition studies are inadequate to properly define the relationship between crops and weeds. A more accurate method for performing such investigations is described in which both weed and crop abundance are determined. These variables are related to crop loss using multiple regression.

Flurazole [phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylate] and acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide] were examined in the laboratory and greenhouse for effects on grain sorghum [Sorghum bicolor (L.) Moench ‘G-522 DR’]. Flurazole did not protect against acetochlor-induced inhibition of primary root growth when sorghum was grown in distilled water, but some safening occurred after 8 days when nutrients were available. Flurazole did not protect primary roots completely. In the presence of nutrients, however, flurazole stimulated growth of the mesocotyl roots and protected the second adventitious root system.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} was evaluated for weed control in winter wheat (Triticum aestivum L.) and for residual effect on soybeans [Glycine max (L.) Merr.] following wheat. Chlorsulfuron applied at 72 g ai/ha and less did not injure or reduce grain yields of ‘Double-Cropped’ wheat. Postemergence tank mixtures of chlorsulfuron at 36 g/ha with diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} at 1 kg/ha were more effective than other treatments for control of wild garlic (Allium vineale L. ♯ ALLVI). ‘Forrest’ soybeans did not show any injury from chlorsulfuron residue even at rates of 72 g/ha when it was no-till seeded following winter wheat.