Comparative Activities of Sodium Tetrathiocarbonate and Metalaxyl on Phytophthora capsici and Root and Crown Rot on Chile Pepper. M. E. MATHERON, Extension Plant Pathologist, University of Arizona, Yuma Agricultural Center, Yuma 85364. J. C. MATEJKA, Research Specialist, University of Arizona, Yuma Agricultural Center, Yuma 85364. Plant Dis. 79:56-59. Accepted for publication 30 September 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0056.

The activities of sodium tetrathiocarbonate (STTC) and metalaxyl on the viability of Phylophthora capsici within colonized pepper tissue, the recovery of P. capsici from soil and the development of root and crown rot on chile pepper were evaluated and compared. P. capsici was not recovered from colonized chile pepper stem tissue buried in soil that was drenched with 4,900 µg/ml of STTC. In contrast, recovery of the pathogen from stem tissue buried in soil drenched with 10 µg/ml of metalaxyl did not differ from that obtained for stem pieces from soil drenched with water only. The number of lesions formed on pear fruit bait incubated with field soil containing P. capsici and treated with STTC at 12 µg/ml was reduced 36% compared with untreated soil, whereas no lesions developed when soil was treated with metalaxyl at 10 µg/ml. Growth of chile pepper seedlings inoculated with zoospores of P. capsici in the presence of STTC at 245 µg/ml or metalaxyl at 10 µg/ml was equivalent to that obtained for plants not inoculated with the pathogen. Root and shoot growth of chile pepper seedlings grown in field soil naturally infested with P. capsici that was treated 1 wk before planting with either STTC at 4,900 µg/ml or metalaxyl at 10 µg/ml was significantly greater than that of plants grown in untreated soil. These investigations demonstrate the potential benefits of STTC as a management tool for the control of Phytophthora root and crown rot of chile pepper.