EARLY BLIGHT CONTROL
Early blight is a very common disease of both potato and tomato. It causes leaf spots and tuber blight on potato, and leaf spots, fruit rot and stem lesions on tomato. The disease can occur over a wide range of climatic conditions and can be very destructive if left uncontrolled, often resulting in complete defoliation of plants. In contrast to the name, it rarely develops early, but usually appears on mature foliage.
HOST PLANTS: Common in potatoes and tomatoes.
SYMPTOMS: On leaves of both crops, the first symptoms usually appear on older leaves and consist of small, irregular, dark brown to black, dead spots ranging in size from a pinpoint to 1/2 inch in diameter. As the spots enlarge, concentric rings may form as a result of irregular growth patterns by the organism in the leaf tissue. This gives the lesion a characteristic "target-spot" or "bull's eye" appearance. There is often a narrow, yellow halo around each spot and lesions are usually bordered by veins. When spots are numerous, they may grow together, causing infected leaves to turn yellow and die. Usually the oldest leaves become infected first and they dry up and drop from the plant as the disease progresses up the main stem.
FAVORED ENVIRONMENT: Early blight overwinters on infected plant tissue and is spread by splashing rain, irrigation, insects, and garden tools. The disease is also carried on tomato seeds and in potato tubers. In spite of its name, early blight can occur any time throughout the growing season. High temperatures (80-85 degrees F.) and wet, humid conditions promote its rapid spread. In many cases, poorly nourished or stressed plants are attacked.
EARLY BLIGHT CONTROL: To avoid early blight, prune or stake plants to improve air circulation. Make sure to disinfect your pruning shears (one part bleach to 4 parts water) after each cut. Keep the soil under plants clean and free of garden debris. Add a layer of mulch to prevent the spores from splashing back up onto vegetation. Water in the early morning hours (avoid overhead irrigation) to give the plants time to dry out during the day. Rotate susceptible crops to other areas of the garden each year. If symptoms of early blight are present, begin applying a copper based fungicide weekly until harvest. Organic fungicides will not kill the disease, but prevent the fungal spores from germinating.