Powdery Mildew on Cucurbits

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Continue to scout cucurbits for powdery mildew. Symptoms typically begin on older, lower leaves and can spread rapidly under dry, humid conditions. Control of powdery mildew begins with regular scouting for symptoms and weekly fungicide applications. Begin a fungicide program when one lesion is found on the underside of 45 leaves. For control of cucurbit powdery mildew in:

Pumpkin and Winter Squash:
Alternate:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Folicur (tebuconazole, 3) at 4.0 to 6.0 fl. oz 3.6F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

With one of the following:
Micronized Wettable Sulfur (M2) at 4.0 lb 80W/A (Sulfur may injure plants especially at high temperatures. Certain varieties can be more sensitive. Consult label for precautions.)
or
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5 to 18.5 oz 38WG/A
or
Quintec (quinoxyfen, 13) at 6.0 oz 2.08F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

When Powdery mildew has become well established in the mid- to late part of the season, only apply protectant fungicides such as chlorothalonil or sulfur.

Summer Squash and Cucumber:
Alternate:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Folicur (tebuconazole, 3) at 4.0 to 6.0 fl. oz 3.6F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

With a tank mix containing:
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5 to 18.5 oz 38WG/A

Muskmelon and Watermelon:
Alternate:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Folicur (tebuconazole, 3) at 4.0 to 6.0 fl. oz 3.6F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

With a tank mix containing:
Quintec (quinoxyfen, 13) at 6.0 oz 2.08F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5 to 18.5 oz 38WG/A

For more information on control of powdery mildew of cucurbits please see the 2010 Delaware Commercial Vegetable Production Recommendations Guide.

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