Cucurbit Downy Mildew – Activity Levels for May 2012

Over the past week, there have been several new reports of cucurbit downy mildew in North Carolina and Georgia.  While these areas are a long distance from Southern Ontario, it is still very important to be vigilant in our approach to this disease.

The relative importance of this disease depends on the type of cucurbit.  Cucumbers are extremely susceptible, followed by muskmelons and watermelons.  While infections may occur in squash and pumpkins, the disease tends to be less virulent in these crops.

In the past few years, cucumber fields grown from transplants were often among the first fields to be identified with downy mildew.  The following steps can help to reduce the risk of infection in these crops.

  1. Ensure all transplants are free from any disease symptoms. Only plant healthy, actively growing transplants.
  2. Grow vegetable transplants in greenhouses used solely for vegetable transplant production.  If transplants are produced in the same greenhouse as commercial greenhouse vegetables, the mature plants may act as a reservoir for crop pests.
  3. Where cucumbers are grown under row covers or tunnels, apply a targeted downy mildew fungicide after field-setting, just prior to covering plants.  Apply a second targeted downy mildew fungicide immediately after the row covers or tunnels are removed.  Melon growers may also choose to apply a preventative fungicide at planting.
  4. After the row covers are removed follow a standard fungicide program based on field scouting and an integrated pest management program.

It is interesting to note that the Michigan State University Vegetable Pathology program reports that they have been catching low levels of downy mildew spores in their traps at two locations in Eastern Michigan (Munroe and Frankenmuth).  For more details, see the article written by Dr. Mary Hausbeck, MSU at http://bit.ly/LdPApB

A map of cucurbit downy mildew outbreaks for 2012 and the current disease forecasts can be found at http://cdm.ipmpipe.org/

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