Verticillium Wilt on Pepper

Pepper Diseases<strong>Verticillium</strong> <strong>Wilt</strong><strong>Verticillium</strong> albo-atrum, V. dahliaFound worldwideSymptomsAffected plants are often scattered sporadically in thefield. Disease symptoms on pepper produced by bothfungi are similar.Symptoms are not usually seen until several weeksinto vegetative growth. In early stages the edges of theleaves will roll inward with some foliar wilting. The plantmay recover from wilting during the night whentemperatures are lower and there is less water stress.Initially, there is some slight stunting and a slightyellowing of the older, lower foliage. The diseasesymptoms move up the plant.As the disease develops, the leaves show moreWorld Vegetable Centeryellowing, and they may drop off, and the plant showspermanent wilting with stunting. There is a dark browndiscoloration present in the vascular section of the stemthat extends from the soil line up the stem into thelower branches of the plant. The affected roots do notshow any external symptoms, in contrast to infectionby Phytophthora capsici, where roots show externaldark discoloration.Conditions for Disease DevelopmentV. dahlia is favored by moderate-to-high temperatureHow to Identify <strong>Verticillium</strong> <strong>Wilt</strong>Gradual wilting of plant; yellowing of lower leavesInternal discoloration of vascular tissue, yetsurface root tissue appears healthyWritten by Ray Cerkauskas, Visiting Scientist from Agriculture and Agri-Food Canada. Edited by Tom Kalb. Photos by E.L. Shannon andJ. C. Watterson. Published by AVRDC – The World Vegetable Center; P.O. Box 42, Shanhua; Taiwan 741; ROCtel: (886-6) 583-7801; fax: (886-6) 583-0009; email: avrdcbox@avrdc.org; www: www.avrdc.org

while V. albo-atrum is favored by cooler temperature.Both fungi survive in soil and crop debris as specializedstructures called microsclerotia. These structuresenable the fungus to tolerate extreme environmentalconditions and lie dormant in the soil for many years inthe absence of a susceptible host. In the presence ofmoisture, root exudates of susceptible plantsstimulate the germination of microsclerotia.The fungus directly penetrates the roots and movesthrough the root tissue to the water-conducting vessels.These become plugged with the fungus, causing plantsto wilt.The fungus is disseminated with infected transplants,irrigation water, wind, on particles of infested soil onfarm implements, machinery, vehicles, and on workershoes.Attack of pepper roots by nematodes will hasten<strong>Verticillium</strong> wilt development.ControlSanitation is crucial since once the fungus is introducedinto the field it may remain indefinitely. If possible, wherelimited infection occurs, destroy infested plant material(including root tissue) after harvest to reduce populationsof the fungus. Eliminate weeds in the production fieldthat may serve as symptomless hosts for the fungusor other susceptible crops that may contribute tobridging the period between susceptible pepper crops.Clean farm utensils and equipment when moving fromone field to another. Wash the soles of shoes afterworking in an infested area. Work in healthy fields firstbefore working in affected fields.For transplant production, use disease-freetransplants, pasteurized soil medium, or fumigatedplant beds. Use proper sanitation measures fortransplant production, and avoid damage to roots duringtransplanting. Treat surfaces with a disinfectant beforeplacing flats there.Temporary flooding will reduce populations ofmicrosclerotia. Do not irrigate a field with watercontaining runoff from other affected fields.Use a long rotation of 3–4 years, including rice,broccoli, corn or sorghum, to allow plant residues todecompose in the soil and to reduce fungal populationsin the soil. Avoid use of tomatoes, potatoes, eggplant,or strawberries in the rotation scheme.Pre-plant soil solarization alone or combined withfumigation, especially using fumigants containingchloropicrin, will reduce fungal populations. This isespecially effective in nethouse, greenhouse or rainshelter production. Maintain a high level of plant vigorwith appropriate fertilization and irrigation to keep plantsless susceptible.Avoid contaminated land. Keep seedling and cropproduction fields away from previous fields infested with<strong>Verticillium</strong>.Resistant pepper cultivars are not available.Control root-knot nematodes and root-feedinginsects since they may help <strong>Verticillium</strong> to establishand spread.For more information on the production ofpepper and other vegetables, go to.AVRDC Publication 04-5812004