How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

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.

COMMENTS ON THE DISEASE

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.

MANAGEMENT

Resistance in peppers to Verticillium wilt is not common in commercial cultivars and is difficult to identify in pepper germplasm. Chemical control of V. dahliae using soil fumigation with methyl bromide and chloropicrin is effective, but not economical for pepper production in California. 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. 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 any case, do not replant peppers in the field for a minimum of 3 years.

PUBLICATION

UC IPM Pest Management Guidelines: Peppers
UC ANR Publication 3460
Diseases
S. T. Koike, UC Cooperative Extension, Monterey County
R. M. Davis, Plant Pathology, UC Davis
K. V. Subbarao, USDA Research Station, Salinas
Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis

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