Late Blight on Potatoes and Tomatoes (6260)

Late blight of tomato and potato is a potentially destructive fungal disease in home gardens. This is the same disease that caused the Irish potato famine in 1845. Late blight can occur at anytime during the growing season when the weather is cool and wet. The disease is slowed down by a return to hot, dry weather. Lesions develop on leaves and stems as dark, water-soaked spots. These spots enlarge until the entire leaf or stem turns brown and dies. Dead leaves typically remain attached to stems. Under favorable conditions, a white mold will appear on leaf undersides. Infected tomato fruits develop shiny, dark, or olive-colored lesions that may cover large areas. Infected potato tubers develop a dry, corky rot that often shows up in storage. When infection is severe, a foul odor is produced in both crops.

Late blight is brought into the garden from infected transplants and seed potatoes or may be blown in from neighboring areas. New strains of the late blight fungus may over-winter in garden soils.

The following steps can be taken to minimize late blight problems:

1. Keep foliage dry; avoid overhead watering; avoid crowding your plants.

2. Always purchase new seed potatoes that are certified disease-free.

3. Do not compost store-bought potatoes, and don't store infected tubers.

4. Pull out and destroy infected plants.

5. Keep developing tubers covered with soil.

6. Apply labeled protectant fungicides, like copper, prior to infection.

For more information on this subject, Please visit the College of Agricultural Sciences Publications Web site.

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