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OSU Extension

College of Food, Agricultural, and Environmental Sciences

July 16, 2015 - 10:42am -- Anonymous

I’ll continue to beat the drum of weather woes with this topic.  Commercial vegetable production is another important component of the Wayne County agricultural economy.  This is turning into a very challenging year for vegetable growers as the wet conditions have allowed some serious fungal diseases to develop.  In early July downy mildew was confirmed in Wayne County.  Downy mildew is a potentially devastating disease of cucurbit crops, but especially cucumbers and cantaloupe.  Pumpkins, squash and watermelon are at less risk of severe damage from downy mildew. 

According to Sally Miller, OSU Extension Vegetable Disease specialist, after downy mildew has been found in the area all growers should be on a fungicide management program.  This is because downy mildew is considered a “community” disease.  It is not going to stay isolated on one farm or field; it can move through the air and spread over a long distance.   The recommendation from Sally Miller is to apply one of the following fungicides on a 5-7 day schedule: Presidio, Ranman, Previcur Flex, Zampro or Tanos.  Whichever product is chosen, it should always be tank-mixed with a protectant fungicide; Bravo or Dithane.  In addition, alternate between fungicides with different modes of action.  See product labels for fungicide rates. Note that the fungicides recommended above have different pre-harvest intervals (PHI).  Keep this in mind when fungicides are applied after harvesting begins.

Two other diseases that both commercial and home tomato growers are struggling with are septoria leaf spot and early blight.  Both of these fungal diseases start at the bottom of the plant and work their way up the plant.  Septoria leaf spot is characterized by small, roughly circular spots that have dark margins and a tan center.  As the disease progresses spots enlarge and can cause premature leaf drop.  Under warm, moist conditions like we have recently been experiencing, defoliation can be rapid.  Early blight symptoms consist of small, irregular, dark brown to black, dead spots ranging in size from a pinpoint to 1/2 inch in diameter. As the spots enlarge, concentric rings may form giving a “bull’s eye” or “target spot” appearance.  There can be a narrow, yellow halo around spots.  As the disease progresses spots can grow together and cause leaf death.  Unlike septoria leaf spot, early blight can also affect the tomato fruit. 

Both diseases generally start by soil splashing onto the lower leaves during a rainfall event.  Control strategies involve mulching around plants to prevent soil splashing, removing and destroying infected leaves, and use of a protectant fungicide such as Daconil (active ingredient chlorothalanil) on a weekly schedule when rains are frequent.

Rory Lewandowski is an OSU Extension Agriculture & Natural Resources educator and may be reached at 330-264-8722.