Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control. Repeat at 5- 7 day intervals during continuous moist weather. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size. Unless the fungus is present on transplants, lesions generally don’t show up until flowering. Temperatures of 17- 24☌ (63- 75☏) and extended leaf wetness favour early blight development. Spores are present throughout the growing season and may be carried long distances in the wind. It is spread by wind and splashing water. The fungus that causes early blight survive on decayed plant material in soil and can be seed borne. Lesions may also appear on stems and blossoms (a cause of blossom drop).įruit infection is uncommon, showing up as a blackened area, similar in appearance to blossom-end rot, but at the stem end of the fruit or as blotches or sunken areas (see Black Mold). Lesions may coalesce to form large dead areas on the leaf. They are often bordered by leaf veins.Įarly blight may cause browning of leaf edges. As lesions enlarge, their shape may become irregular. If the disease is severe, lesions also appear on younger leaves. Lesions become quite large and are often associated with considerable leaf yellowing. The tissue surrounding the spot may be yellow. Spots are circular to angular with dark concentric rings (target spot). Lesions first appear on leaves as dark brown to black spots, 8- 13 mm (5/16- 1/2 in.) in size, on older foliage, but can grow much larger. The first signs of disease often appear deep in the canopy where the leaves stay wet. Applications should continue until close to harvest. Temperatures of 17- 24☌ (63- 75☏) and extended leaf wetness favour early blight development.Įarly blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings. Spores are present throughout the growing season and may be carried long distances in the wind or spread by splashing water. Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.)Įarly blight overwinters in infected crop residue and can be carried by infected seed and weed hosts. Fruit infections are not common, but may appear as a blackened area at the stem-end or dark blotches and sunken areas (see Black Mold)īacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.).Lesions become quite large and are often associated with considerable leaf yellowing.Severe infections spread to younger leaves.Circular to angular spots with dark, concentric rings (target spots) develop on the older foliage.Pruning off low leaves can slow the spread of the disease by reducing the number of spores present.Alternaria tomatophila, Alternaria solani Invisibly small spores are spread to new leaves by wind, rain and insects, where warm, damp conditions encourage them to germinate and grow. When watering tomatoes, avoid wetting the foliage. Use mulches to keep soil from splashing onto tomato leaves. In early summer, clip off the first spotted leaves when you see them, and compost them in an active compost pile. Grow tomatoes at wide spacing in full sun, so their leaves dry promptly each morning and after rains. Try resistant varieties, which are new but very worthwhile. Most of the time early blight weakens plants but does not kill them. Tomatoes can tolerate losing some of their low leaves to early blight, but if persistent rain causes the disease to move more than halfway up the plants, they may be doomed. Early blight spreads fastest in humid weather when temperatures are between 80 and 85F (27-29C). Affected leaves gradually wither to brown and hang on the stems, while leaves higher up on the plant remain green and healthy. The irregularly-shaped spots have concentric rings around their edges, sometimes with a dark dot in the center. The most common cause of dark spots on tomato leaves, early blight begins on the oldest leaves closest to the ground. Worldwide, in temperate climates Description:
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