Greenhouse studies were conducted to evaluate and compare herbicide safeners for protection of corn and sorghum from herbicidal injury from metolachlor, primisulfuron, and the interaction of primisulfuron with terbufos, an insecticide. With the exception of CGA-133205 which killed corn, the safeners oxabetrinil, flurazole, naphthalic anhydride, dichlormid, and R-29148 protected against significant injury from the interaction between primisulfuron (40 g ai ha−1) and terbufos (9.8 kg ha−1 equivalent to 750 g per 1000 m of row) and from metolachlor (6.7 kg ai ha−1). No primisulfuron-terbufos interaction was observed in sorghum and none of the safeners protected sorghum from primisulfuron injury. PRE application of the antioxidants, piperonyl butoxide and metyrapone, increased primisulfuron injury to corn. Piperonyl butoxide by itself did not influence the growth of corn seedlings, but metyrapone caused slight injury. The increased injury from piperonyl butoxide plus primisulfuron applied at 40 g ha−1 was protected by naphthalic anhydride, flurazole, and R-29148, whereas at 80 g ha−1 protection was provided by flurazole and R-29148. None of the safeners tested protected against increased injury from metyrapone. Naphthalic anhydride was also an effective safener against increased corn injury when 3000 ppm piperonyl butoxide was applied foliarly 3 d prior to primisulfuron application. 14C-Primisulfuron absorption by corn was not influenced by piperonyl butoxide or the safener, naphthalic anhydride. However, metabolism of 14C-primisulfuron was inhibited by piperonyl butoxide. This inhibition was not totally reversed by the safener, naphthalic anhydride.

The efficacy of the safeners naphthalic anhydride (NA), CGA-92194, and CGA-133205 as protectants of grain sorghum and of NA, R-29148, CGA-154281, and dichlormid as protectants of corn against injury from the chloroacetamide herbicide, SAN 582H, was evaluated under greenhouse conditions. SAN 582H applied alone reduced the shoot growth of ‘Funk G522DR’ and ‘Funk G623’ sorghum, but had no effect on the growth of the ‘GP-10’ genotype of sorghum. Corn (‘Northrup-King 9283’ hybrid) was considerably more tolerant than grain sorghum to SAN 582H. The rate of SAN 582H causing 50% reduction of corn shoot height (GR50) was 5.1 kg/ha as compared to 1.1 kg/ha for grain sorghum. NA applied as seed dressing at 5 or 10 g/kg seed, provided moderate protection to ‘G522DR’ and ‘G623’ sorghum and no protection to corn against SAN 582H injury. Dressing of sorghum seeds with CGA-133205 provided moderate protection to G522DR sorghum, whereas seed-applied CGA-92194 provided moderate protection to G623 sorghum against SAN 582H. The dichloroacetamide safeners R-29148, dichlormid, and CGA-154281 were all effective as protectants of corn against SAN 582H injury. These results demonstrate that, as with other chloroacetamide herbicides, the tolerance of corn and grain sorghum to SAN 582H can be enhanced with the use of safeners of the dichloroacetamide type and oxime ether type, respectively.

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.