Late Blight, the fungal infection responsible for the Irish Potato Famine, is decimating tomato plants across the East Coast. What makes this infestation so serious is that the infected plants seem to have come from big-box stores that sold large numbers of them, and the cool, rainy weather has aggravated the spread of the fungal spores.

Up to this point tomato and potato plants in Illinois seem to be disease-free, but it would be prudent for gardeners to keep a watchful eye on their plants. The Ohio State University Extension describes the symptoms to look for: "Late blight appears on potato or tomato leaves as pale green, water-soaked spots, often beginning at leaf tips or edges. The circular or irregular leaf lesions are often surrounded by a pale yellowish-green border that merges with healthy tissue. Lesions enlarge rapidly and turn dark brown to purplish-black. During periods of high humidity and leaf wetness, a cottony, white mold growth is usually visible on lower leaf surfaces at the edges of lesions."

Photo Courtesy of Missouri Botanical Garden

If the disease strikes, there isn't really anything to do to save the plants. Late Blight has been likened to the "Bubonic Plague for plants," and any tomatoes or potatoes will be ruined within days. Infected plants should be destroyed at once; DO NOT compost them at home because the spores will likely survive in the compost heap and be spread to other plants.

The best protection from Late Blight is prevention, so if your plants are healthy now be careful with watering practices to avoid the disease. Mulch your tomatoes to prevent splash-back from rainstorms, and water carefully and close to the plants. Spores can be present in the soil; therefore, it's important to keep soil off the plant material. The OSU Extension also recommends using fungicides. Contact your local University of Illinois Extension office or garden center for suggestions about what to use in your area. With the cool and rainy weather continuing, it's crucial for us gardeners to watch for this and other fungal infections that thrive in these conditions.

— Rose Rankin