Verticillium Wilt

Verticillium wilt can affect all cucurbits. The first symptoms are wilting and yellowing of crown leaves, which eventually dry up. Wilting gradually progresses out toward the runner tips; in severe cases, the plant dies. Death may take weeks. A light brown vascular discoloration in roots is sometimes seen in cross section. Aboveground vascular tissue is also discolored and can be seen by cutting through a node near the base of the plant. Tolerant or resistant varieties may show symptoms but seldom die.

Verticillium dahliae survives for years in soil as tiny, dormant sclerotia. The pathogen has a wide host range including many vegetable crops, weeds, and trees. When roots of susceptible crops grow in close proximity, sclerotia germinate and infect the roots. Verticillium wilt is most severe during relatively cool periods and subsides during the hottest part of the summer, but wilting is usually seen during warm dry periods when the plant is under stress, such as after fruit set. The pathogen grows in the water-conducting tissue (xylem), causing plugging and interference with water transport.

Start looking for Verticillium wilt during the vegetative growth stage. Note infections to make management decisions before the next crop. Use tolerant or resistant varieties. Most shipping varieties of cantaloupes grown in California have a moderate degree of resistance, and honeydew melons have greater resistance than cantaloupes. The Persian cultivar is highly susceptible. Do not plant highly susceptible melon varieties in fields with high populations of V. dahliae. For example, avoid fields where cotton was growing if it was severely infected by this disease. Soil solarization has been used experimentally to control this disease in cotton and tomato, but has not been tested in cucurbits because of its expense. Incorporating broccoli residue into the soil can reduce populations of V. dahliae. Also, preplant fumigation with chloropicrin effectively controls this disease but generally is not cost effective.