Differential effects of certain phenoxyacetic acid compounds and phenylcarbamates on plant species. II. Effects of foliage applications with special reference to yields of wheat

The effects of foliage sprays of various phenoxyacetic acid derivatives and of isopropyl n-phenylcarbamate on a dicotyledon, Phaseolus vulgaris, were compared. The carbamate was without effect and although all phenoxyacetic acid compounds were markedly toxic, they differed in the rapidity of their action. Wheat (Triticum vulgare) exhibited differential responses to phenoxyacetic acid compounds and to isopropyl phenylcarbaniate at different growth stages. Applications of four phenoxyacetic acid compounds to wheat at different stages of development, from late seedling to flowering, showed that grain yields were reduced most markedly by applications in the seedling stage; the butyl ester and amine salt of 2,4-dichlorophenoxyacetic acid were more toxic than the sodium salt. 0.1 per cent. foliage sprays of isopropyl phenylcarbamate had no effect on wheat in the late seedling or tillering stages, but severely depressed the yield of grain when applied at flowering. Barley (Hordeum vulgare) responded similarly. Higher concentrations applied to wheat at pre-shooting also reduced grain yields. Flax (Linum sitatissimum), although susceptible to pre-emergence treatment, was not affected by foliage sprays of isopropyl phenylcarbamate at any growth-stage. 0.1 per cent. applications of 2,4-dichlorophenoxyacetic acid as the sodium salt reduced flax yields only when applied at the seedling stage.