Plant Disease Control No. 37
Revised January 1998
Verticillium Wilt of Flowers
Verticillium wilt, caused by the fungus Verticillium albo-atrum, is a disease of many vegetable and fruit crops as well as ornamentals, affecting over 300 plant species. The soil-borne fungus enters the plant through the roots and spreads systemically throughout the water conducting vessels. This results in partial or complete plugging of the vascular system, causing wilting and eventually death of the plant.
SYMPTOMS
Symptoms of Verticillium wilt are most likely to show up when the weather turns warm after a cool period. The foliage of the affected plant turns yellow and wilts, drying up progressively from the base to the top of the plant. If the stem is cut open, a brown discoloration in the vascular system (water conducting tissue) can be observed. The roots are generally not rotted, and usually no cankers or discolorations are visible on the outside of the stem.
CONTROL
Since Verticillium albo-atrum is present in many soils, most control measures are based on preventing infections. Use resistant varieties when possible if a Verticillium wilt problem has been encountered in previous seasons. Keep plants healthy and vigorous with proper fertilization and irrigation, especially during periods of hot weather. Avoid planting in old vegetable gardens or berry patches, because the fungus is probably present in such soil. Always remove and destroy any infected plants.
In important beds, the Verticillium fungus can be controlled by fumigation with Vapam, this fumigant can only be purchased and applied by a certified applicator. Before applying Vapam, always thoroughly cultivate the area to be treated, breaking up clods and loosening the soil deeply. This cultivation should be completed one week before application, and the soil should be kept moist, by watering if necessary. Success depends on how carefully the soil is prepared before application. If the soil is crusted immediately before application, cultivate lightly. Vapam must be applied during a period of moderate air temperature with little or no wind present to prevent evaporation and loss. Soil temperature must be in the range of 60 to 90 degrees Fahrenheit at a 3-inch depth. Be sure to treat at least 3 weeks before planting and to follow all directions on the pesticide label. To avoid killing nearby plants, do not expose them to Vapam.
Sherman V. Thomson/Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician
Listing of commercial products implies no endorsement by the authors or the Utah State Cooperative Extension Service. Criticism of products not listed is neither implied nor intended. Persons using such products are responsible for their use according to the current label directions of the manufacturer. Pesticide labels are legal documents, and it is a violation of federal and state laws to use a pesticide inconsistent with its labeling. The pesticide applicator is legally responsible for its prope
use. Always read and follow the label.