June 14, 2010

Late blight was found on tomato plants in late May in Northern Kentucky. Since then, the disease has shown up on potato and tomato plants in Central Kentucky. A University of Kentucky plant pathologist said it's critical for vegetable producers to scout their plants and take preventative measures to combat this disease.

Late blight is caused by a fungus-like organism. Symptoms include large, water-soaked blotches that turn into green-to-brown lesions on the leaves and stems of infected plants. The disease can quickly increase in severity and spread to other plants if given the right conditions of cool, wet weather. If left untreated, late blight can cause total crop loss.

"In most years, we expect to see very little of this disease and only then at the end of summer," said Kenny Seebold, extension plant pathologist with the UK College of Agriculture. "This marks the second year in a row that this devastating disease of tomatoes has appeared earlier than expected."

Regular fungicide applications are key to late blight prevention. Commercial growers and homeowners can use fungicides with chlorothalonil, maneb, mancozeb or fixed coppers to protect against late blight when disease pressure is low. Organic producers can use products with fixed copper. Fungicides should be applied every seven to 10 days when disease pressure is low and every four to five days if conditions are favorable for the disease to spread. If disease pressure increases or late blight is present, commercial growers can use fungicides specific for late blight control. A full list of these fungicides is available in the June 2 edition of Kentucky Pest News.

Growers with confirmed cases of late blight should destroy the infected plants and all surrounding plants because they could be infected by the disease too. Sunny, dry days are ideal for this because handling wet plants promotes the spread of the disease. Once the infected plants are destroyed, they should be buried. Any debris left lying around could cause additional infections.

Those who have questions about late blight or suspect the disease is present on their crops should contact their local office of the Kentucky Cooperative Extension Service.

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