Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] is a potent synergist of atrazine for postemergence control of weeds such as giant foxtail (Setaria faberi Herrm. ♯ SETFA) and large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA]. We determined whether: a) tridiphane could syngergize the activity of other herbicides known to be detoxified via enzymatic conjugation to glutathione, and b) differential toxicities of the synergized herbicides could provide control of proso millet (Panicum miliaceum L. ♯ PANMI) in corn (Zea mays L. “PAG SXIII”). Four herbicides were used in this study: EPTC (S-ethyl dipropylthiocarbamate), atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], CDAA (N-N-diallyl-2-chloroacetamide), and alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide]. Herbicides and herbicide-synergist combinations were applied postemergence. In corn, tridiphane synergized the activity of EPTC at 2 and 4 kg ai/ha, causing 22 to 25% growth reduction. Atrazine was ineffective and CDAA only slightly effective in combination with tridiphane in causing growth reduction. However, alachlor was markedly synergized by tridiphane at both 2 and 4 kg ai/ha, resulting in 36 to 54% growth reduction compared with plants treated with herbicides alone. Proso millet followed a similar trend to corn: EPTC and alachlor were effectively synergized by tridiphane, while atrazine and CDAA were ineffective. Importantly, however, the rates of herbicide used for proso millet control were much lower than those used for corn. Our data suggest that tridiphane used in combination with EPTC or alachlor could provide improved control of proso millet in corn.

The effects of chloracetamides on protein synthesis were studied both in vivo and in vitro. Four chloracetamide herbicides, alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], CDAA (N–N-diallyl-2-chloroacetamide), and propachlor (2-chloro-N-isopropylacetanilide) were tested for inhibition of [3H]-leucine incorporation into protein. Incorporation of 3H-leucine into trichloroacetic acid (TCA)-insoluble protein was inhibited in oat (Avena sativa L. ‘Victory’) seedlings grown in sand culture and treated 12 h at 1 × 10−4M with these chloracetamides. The herbicides were also tested in a cell-free protein synthesizing system containing polyribosomes purified from oat root cytoplasm. These herbicides had no effect on the rates of polypeptide elongation nor on the synthesis of specific polypeptides when herbicides (1 × 10−4M) were added directly to the system. Polypeptide formation was inhibited 89% when 1 × 10−4M cycloheximide was added during translation. Cytoplasmic polyribosomes were isolated from oat roots treated 12 h with 1 × 10−4M herbicide. Translation rates and products were not altered when these polyribosomes were added to the in vitro system. Protein synthesis is inhibited when tested in an in vivo system; however, the inhibition does not occur during the translation of mRNA into protein.

Buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} may be useful for selective weed control in corn (Zea mays L.) but injures corn seedlings at high rates. Greenhouse studies were initiated to test potential antidotes for buthidazole injury to corn seedlings. NA (1,8-naphthalic anhydride) and CDAA (N,N-diallyl-2-chloroacetamide) were the most effective of six chemicals evaluated. A ratio of 1:3 (buthidazole: CDAA) appeared to be optimal for the protection effect. CDAA appeared to be more effective than NA. Since both CDAA and NA offered limited protection but R-25788 did not, this action appears to be through a different mechanism than the one proposed for the thiocarbamate or acetanilide herbicides. The other chemicals tested were R-25788 (2,2-dichloro-N,N-diallylacetamide), R-29148 (2,2-dimethyl-5-methyl-dichloroace-tyloxazolidine), carboxin (2,3-dihydro-5-carboxanilido-6-methyl-1,4-oxanthiin) and gibberellin (GA3). Seven herbicides, members of the acetanilide, thiocarbamate, and dinitroaniline groups, were also tested for their antagonistic interactions but none offered protection.