Dimethomorph soil and seed treatment of potted tomatoes for control of damping-off and root rot caused by Phytophthora nicotianae var. nicotianae

Two formulations ( 10% emulsifiable concentrate or 50% wettable powder) of dimethomorph were tested as soil or seed treatments for control of damping- off and root rot of tomatoes caused by Phytophthora nicotianae var. nicotia nae (Pnn) Tomato seedlings (cv. UC82B) were groan in pots and inoculated by mixing pasteurised soil with Pnn cultured in vermiculite/V8 juice broth at rates of 0.1, 0.4 or 1% v:v. Root rat was controlled by dimethomorph soil drenches at rates greater than 0.05 g a.i./L. Rates of 2.5 g a.i./L and abo ve were highly phytotoxic, and 10 g a.i./L killed all seedlings. Pre-emerge nce damping-off of seed was controlled by dimethomorph seed treatments at r ates of 10 or 100 g a.i./kg seed in pots inoculated with 1% Pnn, when asses sed at 12 days after sowing. However at 26 and 32 days after sowing only th e 100 g a.i./kg rate of dimethomorph significantly improved the survival of seedlings. None of the seed treatments gave significantly better survival than occurred in an untreated control when pots were inoculated with 0.1% P nn.