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Title: Effect of Cultural Practices and Fungicides on Phytophthora Fruit Rot of Watermelon in the Carolinas

item Kousik, Chandrasekar - Shaker
item ADAMS, M - North Carolina State University
item JESTER, W - North Carolina State University
item HASSELL, RICHARD - Clemson University
item Harrison Jr, Howard
item HOLMES, G - North Carolina State University

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2011
Publication Date: 3/12/2011
Citation: Kousik, C.S., Adams, M.L., Jester, W.R., Hassell, R., Harrison Jr, H.F., Holmes, G.J. 2011. Effect of Cultural Practices and Fungicides on Phytophthora Fruit Rot of Watermelon in the Carolinas. Crop Protection. 30:888-894.

Interpretive Summary: Phytophthora fruit rot of watermelon has caused severe losses to watermelon growers in the southeastern states for the past several years. This disease is considered as an important problem and a top research priority by the National Watermelon Association. We identified several fungicides that were effective in managing Phytophthora fruit rot of watermelon. Of these, Revus and Presidio are two new fungicides that are currently registered for use on watermelon. These fungicides can be used by watermelon growers to manage Phytophthora fruit rot as part of an overall control strategy that also includes crop rotation, the use of well drained fields and proper irrigation practices.

Technical Abstract: Phytophthora fruit rot, caused by Phytophthora capsici, is an important and emerging disease of watermelon (Citrullus lanatus) in the Southeastern U.S. To develop strategies to manage Phytophthora fruit rot, we evaluated the effects of two cultural practices (raised bare ground and plastic mulched beds) used for growing watermelon and various fungicide treatments over three years (2005-2008) and in two locations, North and South Carolina, U.S. The diploid susceptible watermelon cultivar Mickey Lee was used in all the experiments. In each state, fungicides treatments alone or in combinations were used at labeled rates and applied at weekly intervals. Average of 5 spray applications of each fungicide treatment were made at each location and year. Fruit rot incidence was recorded at the end of each trial. Fruit rot incidence in the non-treated plots was 66% across 2 states and 6 trials. Overall, there were no significant differences in the levels of Phytophthora fruit rot between the two cultural treatments. Based on percent disease reduction relative to the non-treated check, the fungicide captan was the most effective across years and locations (range: 23-70%, mean 57%), followed by mandipropamid (25-65%, mean=50%), fluopicolide (24-65%, mean=43%) and cyazofamid (0-48%, mean=31%). Mefenoxam, the current standard treatment reduced fruit rot by 8-28% (mean=18%). The addition of copper hydroxide to the spray mix did not significantly enhance effectiveness of captan or mandipropamid. Mandipropamid, fluopicolide and cyazofamid are relatively new reduced risk fungicides and must be used in rotations or mixed with other broad spectrum fungicides for resistance management. The wide range of fungicide efficacy across locations and years observed in this study emphasizes the importance of local environmental conditions to disease development and management and even when the most effective fungicides are used heavy losses may still follow. Ultimately, for effective control of Phytophthora fruit rot of watermelon, fungicides must be part of an integrated management strategy that at a minimum includes; well drained fields, water management and crop rotation.