Tomato Blight in Wayne County, Ohio

June 28, 2013

Tomato Late Blight in Wayne County, Ohio - Sally Miller, Department of Plant Pathology,; 330-263-3678

Late blight was found today, July 17, 2013, in heirloom tomatoes in Wayne County, OH.  Even though we are currently experiencing very hot conditions that do not favor late blight as cool, rainy conditions do, last week was very conducive to this disease and next week is expected to be a bit cooler.  Therefore, it is very important that both potatoes and tomatoes be scouted regularly (at least twice per week) for late blight.  If late blight is suspected, it can beconfirmed by bringing or sending a sample to the OSU Vegetable Pathology Lab in Wooster ( or the OSU C. Wayne Ellett Plant and Pest Diagnostic Clinic in Reynoldsburg (   We appreciate hearing from you if late blight is suspected so that we can confirm and alert others.

Fungicides such as chlorothalanil (Bravo, Echo, Equus; 0 day PHI) and EBDCs (Dithane, Penncozeb, Manzate; 5 d PHI) and copper-based products (Kocide, Champ, etc.) should be used on a protectant basis on a 7-10 day schedule under conditions not favorable for late blight and a 5-7 day schedule under favorable conditions if late blight has not been detected in the area.  These fungicides also have activity against early blight, but chlorothalanil is the most effective of the three active ingredients against late blight.  

Once late blight is detected nearby or conditions are favorable, add a fungicidewith some systemic (translaminar) activity such as Curzate (3 d PHI), Gavel (5 d PHI), Presidio (2 d PHI), Previcur Flex (5 d PHI), or Ranman (0 d PHI) to the spray tank with the protectant fungicide.  Note the Pre-Harvest Interval (PHI) for these fungicides ranges from 0 – 5 days.


Late blight lesion on top (left) and underside (right) of tomato leaf.  The pathogen is sporulating in a ring around the outside edge of the lesion on the right.


Late blight symptoms on fruit (left) and stems (right).