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Ecology and Epidemiology

Effect of Thiophanate on Epidemic Development of Anthracnose and Yield of Watermelon. K. S. Amin, Plant pathologist, Indian Institute of Horticultural Research, 255, Upper Palace Orchards, Bangalore-560 080, India; B. A. Ullasa, junior plant pathologist, Indian Institute of Horticultural Research, 255, Upper Palace Orchards, Bangalore-560 080, India. Phytopathology 71:20-22. Accepted for publication 13 May 1980. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-20.

Artificial inoculation of watermelon with Colletotrichum lagenarium caused severe anthracnose and yield losses up to 63%. Thiophanate methyl (Topsin-M) sprays applied during early disease development reduced disease severity. Thiophanate sprays protected plants from infection by C. lagenarium for about 20 days, but did not eradicate the fungus from established lesions. Early infection (28 to 45 days after sowing) resulted in severe disease, premature death of plants, and substantial yield loss, while late infection (80 days after sowing) resulted in less yield loss. Protected plants yielded more marketable fruits and fewer diseased fruits. Correlation coefficients between disease indices and infected fruits were positive and significant (P = 0.05), whereas correlations with total fruit yield were negative and significant (P = 0.01). Highest correlations were found between yield loss and disease indices during flowering to fruit formation period. The apparent infection rates of anthracnose were higher on unsprayed plants than on those sprayed with thiophanate.