Certain alkanoyl chloride phenylhydrazones have been found to be active against insects and mites, and also active as herbicides. The phenylhydrazone ring can be substituted. Suitable substituent groups are halogen atoms, the nitro group, the trifluoromethyl group, and alkyl groups of from 1 to 6 carbon atoms, inclusive. The compounds are prepared by reacting an alkanoic acid phenylhy-drazide with phosphorus pentachloride to obtain an alkanoyl chloride (dichlorophosphinyl)phenylhydrazone intermediate that is reacted with phenol to produce the desired alkanoyl chloride phenylhydrazone. Certain compounds can be prepared by direct chlorination of an alkanaldehyde phenylhydrazone. Some of the compounds are novel. Methods of use and compositions are described.