VIEW ARTICLE

Correlation Between Immobilization of Zoospores by Fungicides and the Control of Phytophthora Root and Crown Rot of Transplanted Tomatoes. R. M. Sonoda, Research Assistant, Department of Plant Pathology, University of California, Davis, California 95616, Present address of senior author: Indian River Field Laboratory, P.O. Box 248, Fort Pierce, Florida 33450; J. M. Ogawa(2), T. Lyons(3), and J. A. Hanson(4). (2)Professor, Department of Plant Pathology, University of California, Davis California 95616; (3)(4)Farm Advisor, Sacramento County Agricultural Extension Service; Agricultural Trainee, Department of Plant Pathology, University of California, Davis, California 95616. Phytopathology 60:783-787. Accepted for publication 1 December 1969. DOI: 10.1094/Phyto-60-783.

A fungicide-screening technique based on the reduction in the duration of motility of Phytophthora spp. zoospores was developed. Zoospore suspensions were added to chemical suspensions in several concentrations in a 0.3-ml microbeaker. The time required for the cessation of zoospore motility in this milieu was determined. Two materials, Difolatan and zineb-maneb coordination product (Dithane M-45), previously untested in the field against Phytophthora root and crown rot of transplanted tomatoes as well as captan and copper sulfate, were effective in reducing motility time. As preplant root-dip treatments in the field, Difolatan and Dithane M-45 were more effective than the commercially used captan in retarding the development of foliage symptoms. The plots treated with Difolatan and Dithane M-45 yielded better than the control or captan-treated plots. Copper sulfate seemed to both hasten and increase symptom expression. Basic copper sulfate treatment reduced the yield of tomatoes to a level below the untreated plots. With the fungicides tested, both the poisoned food and greenhouse in vivo screening tests afforded better correlation with field studies than the zoospore immobilization method.