Investigations on fungicides

A series of pyrazole derivatives, which are structural analogues of the systemic fungicide, carboxin (5,6-dihydro-2-methyl-i,4-oxathiin-3-carboxani-lide), have been synthesized and their antifungal properties investigated. 3,5-dimethylpyrazole-i-carboxanilides, although active in vitro and in leaf disk tests, showed no systemic antifungal activity. Certain 3,5-dimethylpyra-zole-4-carboxanilides, however, and their corresponding 1 -methyl derivatives, showed good activity in spore germination tests and high activity against wheat and broad bean rusts in vivo. In several instances, systemic antifungal activity was of the same order as that of carboxin, although generally accompanied by higher levels of phytotoxicity. 1 -Phenyl derivatives were essentially inactive. Substitution in the anilide ring by 3-methyl, 2-methyl or 3-chloro groups resulted in enhanced systemic activity, while 4-chloro, 4-ethoxy, 2-nitro and 3,4-dichloro substituents reduced activity.