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

Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2009
Publication Date: N/A

Technical Abstract: Phytophthora fruit rot caused by Phytophthora capsici is an emerging disease in most watermelon producing regions of Southeast US. It has also been considered as an important problem and a top research priority by the National Watermelon Association (NWA). Managing Phytophthora fruit rot can be difficult because of the long duration of contact between the soil and the fruit, and the difficulty in getting fungicides through the plant canopy to the belly of the fruit. For the past three years (2006-2008), we have been testing several fungicides to manage Phytophthora fruit rot in South Carolina. Based on these trials we have identified three relatively new fungicides with varying levels of effectiveness that have been recently labeled for use on cucurbits. Over the years and under severe fruit rot pressure in our fields, the fungicide Revus (a.i. Mandipropamid, Syngenta) provided 25-67% reduction of fruit rot (mean=52%) compared to untreated check. Presidio (a.i. Fluopicolide, Valent) reduced fruit rot by 30-65% (mean=48%) and Ranman (a.i. Cyazofamid, FMC) reduced fruit rot by 28-47% (mean=36%). Ridomil Gold, the current standard reduced fruit rot by 7-28% in these tests (mean=20%). Another new fungicide, SA-110201 (a.i unknown, Sipcam), was also effective in managing Phytophthora fruit rot (29-59% reduction), but is not yet labeled for use on cucurbits. Resistance in the pathogen population to Ridomil Gold and Ranman has been identified. Thus, there is always a possibility of P. capsici developing resistance to these new fungicides. Therefore these fungicides should be rotated or tank mixed along with some of the available older fungicides to prolong their usefulness. Fortunately, each of these three new fungicides (Revus, Presidio & Ranman) has a different mode of action and therefore can also be rotated among themselves.