Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Downy mildew was diagnosed on cucumbers in both Suffolk County and Northampton County on Delmarva this week. The Suffolk County find was in a small sentinel plot, and the Northampton find was a commercial cucumber field. The commercial field had been sprayed but the infected plants were up against a woods line and the aerial coverage might not have been sufficient to control the disease. If growers have the capability to make ground applications for downy mildew control it would be a good idea to get good coverage of any areas that might not have been covered by aerial applications. Again the recommended fungicides for downy mildew control on cucumbers are Previcur Flex, Ranman, Presidio and Tanos. All need a protectant tank mix partner. Ranman needs a surfactant such as Silwet. Be sure to read the labels for the details and rates. I do not recommend any Ridomil product because the fungus is resistant to that chemistry and Gavel and the phosphoric acid fungicides such as Prophyt and Phostrol are not effective on downy mildew on cucumbers. Fortunately the forecast for Thursday is low risk, be sure to check the forecast at the CDM ipmPIPE website http://cdm.ipmpipe.org for Friday and the weekend. It look like we will get a break in the weather for a short time but it will be important to keep a protectant fungicide on the crop at least.
New Resource for Cucurbit Growers
A laminated 8½ x 11 sheet of the FRAC Guidelines for Downy and Powdery Mildew on cucurbits is now available. These two diseases require frequent fungicide applications and both fungi have developed resistance to fungicides in the past. This quick reference should be helpful for those making fungicide choices in cucurbits, such as cucumbers, cantaloupes, watermelons, squash and pumpkins. These laminated sheets are available in the county offices or we can send you one. To print out your own copy check it out here http://www.rec.udel.edu/Update09/CucurbitDMPMfrac.pdf.