Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
The recent high-pressure system that has brought us the dry weather and low humidity has slowed the progress of any downy mildew that is present. Spray schedules could be extended if the disease is not present or is at low levels. Cucurbits other than cucumbers are probably at low risk until we get some more humidity and dews in the morning. Usually this time of year we can have dew and fog until late morning, which is very favorable for downy mildew. Continue to check the downy mildew forecasting site at NC State for updates. http://www.ces.ncsu.edu/depts/pp/cucurbit/
Growers are having trouble with powdery mildew on pumpkins and other cucurbits at this time of year. This weather pattern has been very favorable for powdery mildew.
For Control of Cucurbit Powdery Mildew In:
Pumpkin and Winter Squash Fields
Alternate
Nova or Rally (myclobutanil, 3) at 5 oz 40WP/A plus chlorothalonil at 2-3 pt 6F/A
or
Procure (triflumizole, 3) at 4-8 oz 50WS/A plus chlorothalonil at 2-3 pt 6F/A
With
Micronized Wettable Sulfur (M2) at 4 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 12.5-18.5 oz 38WG/A
If 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 Fields
Alternate
Nova or Rally (myclobutanil, 3) at 5 oz 40WP/A plus chlorothalonil at 2-3 pt 6F/A
or
Procure (triflumizole, 3) at 4-8 oz 50WS/A plus chlorothalonil at 2-3 pt 6F/A
With
Chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5-18.5 oz 38WG/A
Muskmelon and Watermelon Fields
Alternate
Nova or Rally (myclobutanil, 3) at 5 oz 40WP/A plus chlorothalonil at 2-3 pt 6F/A
or
Procure (triflumizole, 3) at 4-8 oz 50WS/A plus chlorothalonil at 2-3 pt 6F/A
With
Quintec (quinoxyfen, 13) at 6 oz 2.08F/A plus chlorothalonil at 2-3 pt 6F/A
or
Chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5-18.5 oz 38WG/A
For more information on control of Powdery mildew of cucurbits please see the 2008 Delaware Commercial Vegetable Production Recommendations Guide.