LATE BLIGHT ALERT see below

This Week: Late Blight Warning on Greenhouse Tomatoes

From: Dr. Sally Miller, Plant Pathology, OARDC - Wooster

October is the month to start watching out for late blight in your tomato production greenhouses. Late blight, caused by Phytophtora infestans, can destroy a greenhouse full of tomatoes in a matter of a few days. Serious losses to this diseases have occurred in tomato production greenhouse in Ohio at this time of year during the last several years.

Why is this happening? Late blight is a disease that thrives in cool, moist conditions. At this time of year, greenhouses heat up during the warm sunny days and may get very cool at night as temperatures drop. This results in condensation, providing moisture, and cool conditions. IN NEARLY EVERY OUTBREAK OF LATE BLIGHT REPORTED IN GREENHOUSES AT THIS TIME OF YEAR IN OHIO, ADEQUATE SUPPLEMENTAL HEATING WAS NOT PROVIDED AT NIGHT.

How can late blight be avoided? There are several simple steps that can be followed to protect tomatoes from this potentially devastating disease:

1) Maintain temperatures of at least 65 degrees F in the greenhouse.

2) Water plants early so that foliage is not wet after sunset.

3) Scout plants regularly. Look for distinctive symptoms (black lesions on stems and leaves, fuzzy mycelial growth on undersides of leaves, on stems and on fruit, copper-colored lesions on fruit). Pay special attention to areas where condensation or other sources of moisture are heaviest. Also watch out for and repair leaks in the greenhouse (e.g slipped panes, tears in the plastic, etc.) that will allow the cool night air to enter the greenhouse.

4) Maintain proper ventilation and air movement in the greenhouse.

5) Use a protectant fungicide. Dithane formulations (mancozeb) and Exotherm Termil (a fog of chlorothalanil) are labeled for late blight control in the greenhouse. Be sure to follow label instructions and be aware of restrictions.

Pictures of tomato late blight in greenhouses are coming

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