The invention relates to diallyl disulfide and cinnamon oil formulations, for protecting plants from nematodes and other plant pathogens. The invention provides a method for suppressing plant damage by nematodes and other plant pathogens, which comprises the concurrent administration, to the locus, soil or seeds of plants in need of such treatment, of (a) cinnamon oil (and/or its component cinnamaldehyde), (b) an effective quantity of diallyl disulfide, as well as nematocidal compositions useful therein.