Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Phytophthora blight is beginning to show up in summer squash fields in New Jersey. This should be a warning to us here in DE that our cucurbits are also at risk, especially if cucurbits, peppers or other susceptible crops have been grown in the fields. As the early pickles begin to flower this is the time to be planning controls if the crop is at risk from Phytophthora fruit blight. To help suppress development apply mefenoxam or metalaxyl at planting. The following materials will help provide suppression of the fruit rot phase only:
● Forum (dimethomorph, 40) at 6.0 fl oz 4.18SC/A (must be tank mixed with another fungicide active against Phytophthora blight on muskmelon, such as fixed copper
● Gavel (zoxamide + mancozeb, 22 + 3) at 1.5 to 2.0 lb 75DF/A (Note: some muskmelon cultivars are sensitive to Gavel)
● Tanos (famaxodone + cymoxanil, 11 + 27) at 8.0-10.0 oz 50DF/A
● Ranman (cyazofamid, 21) at 2.75 fl oz 400 SC/A (plus an adjuvant, see label for details)
● Presidio (fluopicolide, 43) 4.0 fl oz/A; plant back or rotation restrictions of 180 days for all crops other than cucurbits and fruiting vegetables. See label for details.
Phytophthora fruit rot of watermelon