![]() ![]() Keep this year’s field at least 225 to 450 yards away from last year’s field. Do not use a field for potatoes that was used for potatoes or tomatoes the previous year. Do not dig tubers until they are fully mature in order to prevent damage. Keep plants healthy stressed plants are more predisposed to early blight. In general, late maturing varieties are more resistant than the earlier maturing varieties. Varieties resistant to this disease are available. Early blight spots are less likely to become rotted by secondary organisms than the other tuber rots. As the disease advances, the potato flesh often becomes water soaked and yellow to greenish yellow. When the tuber is sliced open, the flesh under the spots is usually brown, dry, and leathery or corky in texture. The edges of the spots are often raised and purple to dark metallic gray in color. Tubers are affected, as well, with dark, circular to irregular spots. Dark brown to black spots can occur on stems. This is especially true on the lower leaves, where spots usually occur first and can be very abundant. As the spots become very large, they often cause the entire leaf to become yellow and die. A yellowish or greenish-yellow ring is often seen bordering the growing spots. The spots usually have a target appearance, caused by concentric rings of raised and depressed dead tissue. The spots are often bordered by veins that make them angular. ![]() Spots begin as small, dark, dry, papery flecks, which grow to become brown-black, circular-to-oval areas. Early blight is favored by warm temperatures and high humidity. This disease, also known as target spot, rarely affects young, vigorously growing plants. The terms “early” and “late” refer to the relative time of their appearance in the field, although both diseases can occur at the same time.Įarly blight of potato is caused by the fungus, Alternaria solani, which can cause disease in potato, tomato, other members of the potato family, and some mustards. Both are found everywhere potatoes are grown. Using an appropriate organic herbicide (or removal by hand) would be viable organic approaches to Strategy 5.Early blight and late blight, two serious diseases of potato, are widely distributed. Strategies 1, 2, 3, 4 and 6 are strictly organic approaches. Follow harvest restrictions listed on the pesticide label. Apply chlorothalonil, maneb, macozeb, or a copper-based fungicide, such as Bordeaux mixture, copper hydroxide, copper sulfate, or copper oxychloride sulfate. Apply at 7 to 10 day intervals throughout the season. Fungicides will not cure infected leaves, but they will protect new leaves from becoming infected. If the above measures do not control the disease, you may want to use fungicidal sprays. ![]() Wait 1–2 years before replanting tomatoes in these areas.ħ. Next year do not plant tomatoes back in the same location where diseased tomatoes grew. Nightshade and horsenettle are frequently hosts of Septoria leaf spot and should be eradicated around the garden site.Ħ. Use a soaker hose at the base of the plant to keep the foliage dry. Overhead watering facilitates infection and spreads the disease. Mulching will reduce splashing soil, which may contain fungal spores associated with debris. If the plants can still be handled without breaking them, stake or cage the plants to raise them off the ground and promote faster drying of the foliage.ģ. Improve air circulation around the plants. At the end of the season, collect all foliage from infected plants and dispose of or bury. However, removing leaves above where fruit has formed will weaken the plant and expose fruit to sunscald. If caught early, the lower infected leaves can be removed and burned or destroyed. Long periods of high relative humidity, temperatures of 60–80 degrees F, and leaf wetness are ideal conditions for development and spread of the pathogen.ġ. The fungus can also survive on equipment such as plant stakes and cages. The fungus overwinters on infected tomato debris or on weeds in the nightshade family, the same family to which tomatoes belong. If leaf lesions are numerous, the leaves turn slightly yellow, then brown, and then wither. This disease spreads upwards from oldest to youngest growth. Characteristically, there are many spots per leaf. Spots are circular, about 1/16 to 1/4 inch in diameter with dark brown margins and tan to gray centers with small black fruiting structures. Septoria leaf spot usually appears on the lower leaves after the first fruit sets. It is one of the most destructive diseases of tomato foliage and is particularly severe in areas where wet, humid weather persists for extended periods. Septoria leaf spot is caused by a fungus, Septoria lycopersici. Septoria leaf spot on tomato ( Lycopersicon) ![]()
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