Verticillium Wilt

Verticillium dahliae can infect pepper plants at any growth stage. Symptoms include yellowing and drooping of leaves on a few branches or on the entire plant. The edges of the leaves roll inward on infected plants, and foliar wilting ensues. The foliage of severely infected plants turns brown and dry. Growth of pepper plants inoculated with aggressive strains of V. dahliae in greenhouse or of pepper plants infected early in the season under field conditions is severely stunted with small leaves that turn yellow-green. Subsequently, the dried leaves and shriveled fruits remain attached to plants that die. Brown discoloration of the vascular tissue is visible when the roots and lower stem of a wilted plant are cut longitudinally. Another important soilborne disease of pepper in California, Phytophthora root rot, causes similar foliar symptoms; however, Phytophthora root rot causes extensive browning and rotting of the root cortex, while the roots of V. dahliae-infected pepper plants show no external discoloration or decay.

Verticillium wilt, caused by Verticillium dahliae, is a soilborne fungus that colonizes the vascular tissues of plants. Verticillium dahliae has a broad host range, causing vascular discoloration and wilt of many economically important crops. Microsclerotia produced by V. dahliae may survive under field conditions for up to 14 years in the absence of a host. The microsclerotia germinate in the vicinity of host roots and cause infection. Verticillium wilt is favored by cool air and soil temperatures. Peppers are resistant to isolates of V. dahliae from many hosts, and only certain strains of V. dahliae, such as those from eggplant and pepper, are pathogenic on peppers. In recent years, an increase in the incidence of Verticillium wilt on many types of pepper has been observed in the central coast of California, resulting in significant reduction in yields.

There are no effective control methods once the disease has occurred in the field; therefore management strategies should concentrate on avoiding the problem.

• Resistance to Verticillium wilt in commercial cultivars of peppers is not common and is difficult to identify in pepper germplasm.
• Because of the longevity of microsclerotia and the broad host range of V. dahliae, crop rotation is usually not a feasible option for control of Verticillium wilt in many crops. However, rotations with broccoli, corn, wheat, barley, sorghum or safflower for a period of at least 2 years (the longer the rotation, the better) can reduce inoculum and subsequent plant infection. These crops are not hosts for the Verticillium pathogen, and populations of the pathogen will decline in fields where host plants are not present. In severe cases, do not replant peppers in the field for a minimum of 3 years.
• Clean equipment and tractors before entering a new field to prevent the spread of soilborne pathogens such as V. dahliae.

Check for symptoms of Verticillium wilt through fruit development and keep records of infections in order to make decisions for future plantings.

Preplant soil fumigation with metam sodium is usually not economically viable for controlling Verticillium wilt in peppers. However, when metam is applied to the soil for weed control, concurrent reductions of Verticillium propagules often occur.