Vegetable Disease Update – July 2, 2010

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

Cucurbit Downy Mildew
We are at minimal risk at the present but keep up to date by checking the ipm PIPE website http://cdm.ipmpipe.org regularly for updates. Downy mildew was found in New York state for the first time on cucumber in Erie and Niagara counties close to the Ontario, Canada infection site. The northern march of downy has been slowed. We have had some weather patterns coming north but the clear skies and plenty of UV radiation have probably been keeping viable spore number low. We are checking our sentinel plots weekly for downy mildew here in DE.

Bacterial Wilt
Bacterial wilt on slicing cucumbers was diagnosed this week. Symptoms on this planting were random wilting of several runners on 20% of the plants. Sticky strands of bacterial ooze can be seen when the cut ends of the wilted runners are touched together then slowly drawn apart. Striped and spotted cucumber beetles carry the bacteria on their mouthparts and inoculate them when they feed on the succulent stems early in the season. Bacterial wilt is not seed borne and does not persist in the soil more than 2-3 months. It is thought that the bacteria acquire the bacteria from infected weed or volunteer cucurbit hosts. Cucumber beetle control is the primary control method.

Strands of bacterial ooze from touching cut ends of infected runner and pulling them apart slowly

Potato and Tomato Late Blight Webinar for Home Gardeners
Rutgers, Penn State and Cornell University vegetable plant pathologists will be holding a Webinar on Potato and Tomato Late Blight for home gardeners on July 13, 2010 at 6:30 PM. You are encouraged to participate in this timely topic. The linked announcement has all the information to enroll. It will be a good review for commercial producers as well.

Pythium Blight or Cottony Leak on Snap Beans
Pythium blight or cottony leak on snap beans was diagnosed early this week. This disease likes the hot, humid conditions that we had before this recent break in the weather. When we go back to the humid weather again with scattered showers and irrigation this disease can be a threat. Look for the cottony white growth in the lower canopy and on pods close to the ground. There is a 24c registration for Ridomil Gold Copper (2 lbs/A) for prevention of Pythium blight in DE, MD and VA. Several applications may be necessary if favorable weather persists.

Cucurbit Powdery Mildew
Powdery mildew on cucurbits has been reported in New Jersey. Delaware growers should be scouting and begin applying fungicides for powdery mildew once 1 old leaf in 45 has been found with powdery mildew. See the article titled Powdery Mildew on Cucurbits in WCU 18:15 for suggested fungicides.

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