Verticillium wilt, caused by two species of soil-borne fungi can become a problem in greenhouse vegetable production. Sometimes, both species will occur in the same field. A yellowing of lower leaves followed by wilting is the first sign of disease. Lesions have a characteristic V-shaped pattern which is widest at the leaf margin. Brown, necrotic tissue within lesions is surrounded by a large, irregular area of yellowing due to a systemic leaf toxin produced by the fungi. Symptoms are subtle and may be confused with insufficient moisture or other vascular wilts. Because Verticillium affects the water-conducting vessels, symptoms can appear on one side of the plant or on one side of a leaf. Leaf necrosis is followed by wilting, stunting, and plant death. When the stems of infected plants are cut lengthwise, the vascular tissue exhibits a brown discoloration. Verticillium species survive in the soil and on infested crop residues as microsclerotia or resistant mycelium and in symptomless weed hosts. Infection generally occurs through wounds in the roots caused by cultivation or nematode damage. The disease is favored by cool weather and high soil pH. There is no effective chemical treatments for Verticillium Wilt, short of soil sterilization by steam, broad spectrum fumigants, or soil solarization. Practice long crop rotations including cereals or fodder grasses. Remove and destroy infested crop debris well away from production fields. Control weeds. Consider mustard green manures.
Posted on: Thu, 11 Dec 2014 09:51:02 +0000
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