SUMMARYTecnazene (up to 33 ppm) and dichloran (up to 500 ppm) had little effect on germination of spores or growth ofFusarium solaniisolated from and causing a rot of potato tubers; they also did not decrease rotting when applied to wounds later inoculated with the pathogen.Benomyl and thiabendazole (up to 500 ppm) also had little effect on spore germination but did greatly decrease growth at 5 ppm. A pronounced pink coloration developed in cultures growing slowly in the presence of benomyl; a similar though less striking effect appeared in agar cultures containing thiabendazole.Benomyl suspended in water or diluted with Fuller's earth gave good control of rotting when applied to wounds inoculated later withF. solani.Still better control was obtained with thiabendazole; dusts containing 1% a.i. substantially decreased rots and those containing 10 % a.i. gave almost complete control when applied to wounds shortly before inoculation. Thiabendazole was also very effective when used 24 h after inoculation and a fair measure of control was obtained when it was applied 24 h later.Benomyl and thiabendazole placed on apparently intact surfaces of tubers caused tissue 5 mm deep to become toxic toF. solani10 days later, and, unexpectedly, this tissue prevented spore germination.Fuller's earth alone substantially decreased rotting.The results obtained suggest that dusts containing thiabendazole have some promise for the control ofFusariumrots of potato tubers, especially of early crops.