Adsorption of five phenylurea herbicides, metobromuron [3-(p-bromophenyl)-1-methoxy-1-methylurea], monolinuron [3-(p-chlorophenyl)-1-methoxyl-1-methylurea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea], and CGA-15646 [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea] by eight selected soils of Czechoslovakia were studied. Constants from Freundlich and Langmuir equations were calculated and correlated with the major soil properties. Freundlich K values ranged from 1.84 to 128, and the Freundlich equation was better fitted to the adsorption isotherms than was the Langmuir equation. Soil organic-matter content was the most important factor influencing the range of adsorption.

Preemergence application of chloramben (3-amino-2,5-dichlorobenzoic acid) at 5.0 and 6.7 kg/ha, chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] at 2.2 kg/ha, and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] + nitralin [4-(methyl-sulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 1.1 + 1.1 kg/ha controlled 95% or more of the barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), red-root pigweed (Amaranthus retroflexus L.), Powell amaranth (A. powellii S. Wats.), and hairy nightshade (Solanum sarachoides Sendt.), but reduced stands and injured direct-seeded asparagus (Asparagus officinalis L. ‘UC-66’). Linuron at 1.1 kg/ha controlled only 84% of the barnyardgrass and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.6 kg/ha controlled about 50% of the hairy nightshade. Activated carbon applied at 56 and 112 kg/ha in a 3-cm band over the seeded row protected the asparagus from chloramben at 5.0 kg/ha, chlorbromuron at 2.2 kg/ha, and linuron + nitralin at 1.1 + 1.1 kg/ha. Weed control generally was reduced about 10% in the carbon band, but control was still 85 to 90%. Metribuzin reduced asparagus stands and vigor severely, even when 112 kg/ha of activated carbon was applied.

Preliminary greenhouse studies indicated the presence of a synergistic interaction between low rates of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in combination with linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea]. In a 3-yr field study, moderate injury of cotton (Gossypium hirsutum L. ‘Stoneville 213’) with no yield reduction was observed with fluometuron or diuron at 1.68 and 1.12 kg/ha, respectively, but higher rates (5.04 and 3.36 kg/ha, respectively) caused injury and yield reductions. Soybean [Glycine max (L.) Merr. ‘Hill’] injury ratings during the second year indicated a synergistic interaction between residue from fluometuron at 5.04 kg/ha combined with linuron at 2.48 kg/ha or chlorbromuron at 3.85 kg/ha, and from diuron at 3.36 kg/ha combined with linuron at 2.48 kg/ha. These interactions were not apparent in soybean yield data. Soybean injury the third year ranged from 30 to 60% with single or repeated applications of linuron or chlorbromuron, although yields were not affected. Residual fluometuron and diuron from 2 yr of application at 5.04 and 3.36 kg/ha, respectively, injured soybeans, but did not reduce yields. Significant synergistic interactions were observed through injury and yield measurements after two annual applications of fluometuron at 5.04 kg/ha combined with linuron or chlorbromuron. A synergistic interaction was detected in soybean yields with chlorbromuron at 3.85 kg/ha preceded by two annual applications of diuron at 3.36 kg/ha. Such interactions may occur under field conditions, but are unlikely to be economically significant. Chemical analysis indicated little evidence of accumulation, even with repeated application of fluometuron or diuron at 5.04 and 3.36 kg/ha, respectively.

Six herbicides were evaluated at two rates on sweet potatoes [Ipomoea batatas (L.) Lam. ‘Georgia Red’, ‘Georgia Jet’] with and without cultivation from 1972 through 1976. Cultivation with a ground-driven rotary hoe about 2 weeks later improved the control of late-season broadleaf weeds such as Florida beggarweed [Desmodium tortuosum (Sw.) DC] and showy crotalaria (Crotalaria spectabilis Roth.). Cultivation improved weed control where vernolate (S-propyl dipropylthiocarbamate), DCPA (dimethyl tetrachloroterephthalate), and napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] were applied. The improved weed control in cultivated treatments resulted in increased sweet potato yields in 1972 and 1973, which also were the years with the highest weed populations.