Downy Mildew Update – July 12th, 2012

Since the initial report of downy mildew in Elgin county last week, there has been very little activity across the cucumber growing region.  To date, the disease has been confirmed in only two fields in Ontario.  Hot, dry temperatures will certainly slow the development of this disease.  However, don’t let the weather fool you. It is important to maintain a regular preventative fungicide program. Morning dew in a dense canopy often takes several hours to dry.  At a temperature of 20 C, it only takes two hours of leaf wetness for infection to occur.

Many melon, squash and pumpkin growers are wondering if they also need to follow a targeted downy mildew program. Pumpkins and squash are typically less susceptible to downy mildew.  However, it is still important to scout these crops regularly to ensure that if the disease does become established it is identified as early as possible.  These growers may choose to follow a broad-spectrum fungicide program using products such as chlorothalonil or manzate to protect the crop against other diseases such as powdery mildew, athracnose and alternaria.  Growers may decide to include a downy mildew targeted product in the rotation, if downy mildew is identified in a cantaloupe, squash or pumpkin crop in the great lakes region.