Verticillium wilt, caused by two species of soil-borne fungi-Verticillium dahliae and Verticillium albo-atrum, infects more than 200 species of plants, including many vegetables. V. albo-atrum prefers cooler soils while V. dahliae 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, secondary root formation, or plant parasitic nematode feeding. Both species are capable of long term survival in the soil. The disease is favored by cool weather and neutral to alkaline soils.
Cultural Controls & Prevention:
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 with non-susceptible hosts. Benefits of this technique are limited by the extremely wide host range of the pathogens. Cereals or grasses should be included in the rotation.
- Remove and destroy infested crop debris well away from production fields.
- Control weeds in both the main crop and rotational crop, as many weeds are also hosts for Verticillium.
- Consider green manures, especially of cruciferous crops, to stimulate natural microflora and reduce plant pathogen activity and survival.
Chemical Controls & Pesticides:
For Current information on disease recommendations ins specific crops including information on chemical control & pesticide management, please visit the New England Vegetable Management Guide website.