Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Heavy local rains across Delmarva have heightened concerns about Phytophthora fruit and crown rot of many vegetables. Phytophthora is a notoriously difficult disease to manage. Cultural practices to make field conditions less favorable for Phytophthora are necessary for management. Always reduce standing water as much as possible in season by growing plants on raised beds and avoiding planting in areas of the field that are prone to accumulation of standing water. Subsoil, avoid over irrigation if possible, and avoid using water that is contaminated with Phytophthora capsici (ponds may become contaminated). Phytophthora-tolerant pepper cultivars are available. In-season management recommendations for different crops is below.
Watermelon
Sprays targeted for Phytophthora fruit rot should begin when fruit are approximately grapefruit size.
In trials conducted over the last ten years in South Carolina on managing Phytophthora fruit rot with fungicides, a good program was Actigard plus Prophyt plus Kocide applied and alternated with an application that includes Zampro, or Revus or Presidio. Zampro, Revus, and Presidio applied four days before harvest performed well in reducing post-harvest rot. I haven’t seen any data on Orondis on Phytophthora, but I would expect it to be an effective material, also.
As I mentioned this disease is difficult to manage and in fields that are sprayed weekly for four or five weeks, fruit rot will only be reduced by 60 to 75%. Therefore, even in treated fields many fruit won’t be harvestable.
Pepper
The crown rot phase of Phytophthora can be managed with an application of Ridomil 4SL at planting, and one additional time 30 days later, through the drip line. Between Ridomil applications Presidio or Ranman can be applied through the drip. The aerial phase of the disease is best managed with applications of a tank mix of copper with Presidio, Revus, Ranman, Forum or Zampro and alternated with Ridomil Gold Copper.
Eggplant
The crown rot phase of Phytophthora on eggplant can be managed with drip line applications of Ridomil 4SL at planting and 30 days later. Between Ridomil applications Presidio can be applied through the drip.
The aerial phase of the disease can be suppressed on eggplant by in a tank mix of a copper fungicide with Presidio, Ranman or Forum.