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Title: Fungicide rotation schemes for managing Phytophthora fruit rot of watermelon in southeastern United States

Author
item Kousik, Chandrasekar - Shaker
item JI, PINGSHENG - University Of Georgia

Submitted to: International Phytophthora Capsici Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/26/2013
Publication Date: 12/2/2013
Citation: Kousik, C.S., Ji, P. 2013. Fungicide rotation schemes for managing Phytophthora fruit rot of watermelon in southeastern United States. International Phytophthora Capsici Conference. pp 19.

Interpretive Summary: N/A

Technical Abstract: Fruit rot, caused by Phytophthora capsici is a prevalent disease in most watermelon producing regions of the world. The disease was first reported in 1940 in Florida. It is particularly severe in the southeastern United States, where about 50% of the watermelon fruit are produced (FL, GA, AL, SC, NC, and VA). In addition, optimal conditions for disease development are generally prevalent in these states. In 2012 and 2013, growers in NC, SC, and GA, incurred significant losses due to pre- and post-harvest Phytophthora fruit rot, and therefore the National Watermelon Association (NWA), a grower consortium, considers fruit rot as a top-research priority. In previous trials conducted in NC and SC, we identified several fungicides that were effective in managing Phytophthora fruit rot of watermelon. The present studies were conducted in Charleston, SC, and Tifton, GA, to determine fungicide rotations that would be effective in managing fruit rot. A total of five foliar applications were made at each location. Phytophthora fruit rot was very severe at both locations in 2013 with 76% and 63% fruit rot in the non-treated plots in Tifton and Charleston respectively. In Tifton, the fungicide rotation scheme of Presidio alternated with Zampro, Presidio alternated with V-10208, and Presidio alternated with Revus/Ridomil Gold/Ranman/K-Phite appeared to be the most effective in disease reduction compared to non-treated control. Ridomil Gold applied alone or in conjunction with Ranman also reduced disease significantly compared with the non-treated control. In Charleston, all the fungicide rotation schemes provided significant reduction of disease compared to non-treated control. The rotation treatments that were effective in Tifton were similarly effective in Charleston. The fungicide rotation of Presidio alternated with Zampro was the most effective when data from the two locations were combined and it reduced fruit rot by 50% compared to non-treated control. This was followed by the treatment where Presidio was alternated with V-10208 (46% disease reduction over non-treated control), tank mix of Ranman + Ridomil Gold (43%), and the rotation scheme of Presidio/K-Phite/Presidio/Ranman + Ridomil Gold/Revus (42%) respectively. During the time when these studies were conducted, heavy rainfall was prevalent, particularly in Tifton area resulting in severe monetary losses to several growers due to pre- and post-harvest fruit rot. The present study indicates that fruit rot can be managed to some extent under extreme conditions. However, it may not be possible to get complete control of the disease under extremely wet conditions and an integrated management approach will need to be adapted to get adequate control.