How to Get Rid of Verticillium Wilt
Gardeners who love a challenge will find verticillium wilt (Verticillium dahliae and Verticillium albo-atrum) a worthy enemy. Affecting the vascular systems of plants, which transport water, verticillium wilt causes leaves to turn yellow between their veins, and then leaves, shoots and branches die. Symptoms progress from plant bases or branches to their tips, and in woody plants, one side is often affected before the other. The fungi responsible for verticillium wilt live in soil and persist from year to year, infecting susceptible plants. Providing good growing conditions through fertilizing and watering, removing infected plant material, growing resistant plants and sterilizing the soil with solarization, are effective weapons to battle verticillium wilt.
Fertilize trees and shrubs suffering from verticillium wilt as soon as symptoms appear. Apply ammonium sulfate at a rate of 3 pounds per 100 square feet. Work the fertilizer into the top few inches of soil around the drip line of trees and underneath shrubs. Water it in.
Water trees and shrubs at the first sign of infection, applying water within the drip line at a rate of 6 to 12 gallons per square foot. Repeat every 10 to 14 days during dry weather in the growing season.
Prune branches killed by verticillium wilt with pruning shears or a pruning saw, cutting 5 or 6 inches below the area of discoloration. Remove prunings from the garden and disinfect pruning tools between plants, by wiping 70-percent rubbing alcohol over the blades.
Remove and dispose of trees and shrubs severely infected with verticillium wilt that don't respond to feeding and watering. Replace with resistant cultivars.
Go Get 'Em Greens
Fertilize plants growing in infected areas to limit the spread of disease. Dilute 1 tablespoon of 24-8-16 fertilizer per gallon of water and apply at a rate of 1 gallon every 10 square feet every two weeks or according to the manufacturer's instructions.
Water plants sparingly during dry periods, so that the ground is moist but not sodden.
Sterilize bare soil through solarization in late spring or summer. Water growing beds to a depth of 12 inches. Dig a narrow trench 4 to 6 inches deep around a bed, and bury the edge of a sheet of thin clear plastic in a trench on one side by covering it with soil. Pull the plastic sheet over to cover the bed. Exclude as much air as possible from beneath the plastic and bury the remaining edges in trenches to secure it. Leave the plastic in place for four to six weeks and then remove it and plant the bed, avoiding disturbing soil deeper than 6 inches below the surface.
Plant resistant cultivars in areas affected by verticillium wilt and practice five-year rotations in annual planting areas.
Dig up and dispose of plants killed by verticillium wilt, removing as many roots from the soil as possible.
- University of California Statewide Integrated Pest Management Program: Verticillium Wilt -- Verticillium Dahliae and V. Albo-Atrum
- University of Illinois Extension: Verticillium Wilt Disease
- American Phytopathological Society: Verticillium Wilt
- Colorado State University Extension: Caring for Trees in a Dry Climate
- Missouri Botanical Garden: Begonia (Tuberosa Group)
- Missouri Botanical Garden: Heuchera Sanguinea
- The average garden hose delivers 10 gallons of water every 5 minutes.
- Painters' plastic, which is available at hardware stores, is suitable for solar sterilization. Very thin 1-mil plastic provides the most heat, but it tears easily. Plastic up to 4 mil is effective. One mil equals 0.001 inch.
- Plants resistant to verticillium wilt include tuberous begonias (Begonia tuberosa) and coral bells (Heuchera sanguinea). Begonias are hardy in U.S. Department of Agriculture plant hardiness zones 9 through 11, grow 12 to 18 inches tall and wide, and bear flowers in a range of colors summer through early fall. Coral bells bear red spring and summer flowers, grow 12 to 18 inches tall and 9 to 12 inches wide, and are hardy in USDA zones 3 through 9.
- Don't dig in soil sterilized by solarization. Only the top 6 inches or so are sterile and verticillium wilt spores may exist in lower layers.
- Don't put plants suffering from verticillium wilt in compost bins or use chipped woody plants as mulch as this may spread the disease.
A graduate of Leeds University, Jenny Green completed Master of Arts in English literature in 1998 and has been writing about travel, gardening, science and pets since 2007. Green's work appears in Diva, Whole Life Times, Listverse, Earthtimes, Lamplight, Stupefying Stories and other websites and magazines.