Retention of Fungicides for Control of Alternaria Leaf Blight of Muskmelon Under Greenhouse Conditions. H. Suheri, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. R. X. Latin, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907. Plant Dis. 75:1013-1015. Accepted for publication 20 March 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1013.

Retention of chlorothalonil and mancozeb deposits on muskmelon leaf surfaces in the greenhouse was determined using a biological cellophane bioassay with Alternaria cucumerina as the test organism and inhibition of spore germination as the response variable. The bioassays were performed on plants exposed to wet and dry conditions. A linear relationship resulted between inhibition of spore germination and exposure time for all treatments. Differences in retention among treatments were negligible under dry conditions. However, significant differences in retention occurred after treated plants were exposed to a wet regime; the rate of loss of mancozeb was significantly greater than the loss rate of chlorothalonil. No improvement in retention occurred when a surfactant was added to the mancozeb fungicide.