ARS | Publication request: New Fungicides for Managing Phytophthora Fruit Rot of Watermelon

Submitted to: Vineline Magazine
Publication Type: Trade Journal
Publication Acceptance Date: April 15, 2008
Publication Date: May 1, 2008
Citation: Kousik, C.S., Holmes, G.J., Adams, M.L. 2008. New Fungicides for Managing Phytophthora Fruit Rot of Watermelon. Vineline Magazine. pp 30.

Technical Abstract: For the past several years, Phytophthora fruit rot of watermelon (causal agent: Phytophthora capsici) has been considered an important problem and a top research priority by the National Watermelon Association. Management of Phytophthora fruit rot is particularly difficult because of the long duration of contact between the soil and fruit, and the difficulty in getting fungicides through the plant canopy to the belly of the fruit for protection. Since 2005, we have been testing fungicides to manage Phytophthora fruit rot in North and South Carolina. Three new fungicides with varying levels of effectiveness have been recently labeled for management of Phytophthora on cucurbits. Over the years and under severe fruit rot pressure in our fields, the fungicide Revus (a.i. Mandipropamid, Syngenta) provided 12-76% reduction of fruit rot. Presidio (a.i. Fluopicolide, Valent) reduced fruit rot by 30-60% and Ranman (a.i. Cyazofamid, FMC) reduced fruit rot by 23-46%. Ridomil Gold, the current standard reduced fruit rot by 0-29% in these tests. The wide range of fungicide effectiveness emphasizes how important local conditions are to disease development and management. Resistance in the pathogen population to Ridomil Gold and Ranman has been identified. There is always a possibility of Phytophthora developing resistance to these new fungicides. Therefore to prolong their life, these fungicides should be rotated along with some of the available older fungicides (e.g., chlorothalonil and mancozeb). Fortunately, each of the new fungicides has a different mode of action and can be rotated among themselves effectively.