Development of Pre- and Postharvest Phytophthora Fruit Rot on Watermelons Treated with Fungicides in the Field

Fruit rot, caused by Phytophthora capsici, is a serious disease in most watermelon producing regions in the southeastern United States and has caused devastating losses over the past few years. Experiments were conducted from 2010 to 2013 in a P. capsici-infested field to identify fungicides effective for managing pre- and postharvest development of Phytophthora fruit rot. Weekly treatments of OXTP (Oxathiapiprolin), V-10208 (ethaboxam), Zampro (ametoctradin+dimethomorph), Forum (dimethomorph), Prophyt (potassium phosphite) + Kocide 2000 (copper hydroxide), Revus (mandipropamid) rotated with Prophyt + Kocide, and rotations of Revus with Presidio (fluopicolide) and Actigard with Revus significantly reduced preharvest fruit rot in the field compared to nontreated control. Symptomless fruit harvested four days after the last spray was inoculated with P. capsici and maintained in a humid chamber to evaluate postharvest fruit rot development. OXTP, Zampro, Forum, V-10208, Presidio rotated with Revus, and Actigard rotated with Revus applied in the field provided extended postharvest protection compared to nontreated control. Many of these fungicides belonging to different FRAC group should be used in rotations to manage Phytophthora fruit rot of watermelon and should be part of an overall management strategy that also includes use of well drained fields and proper irrigation practices.