Verticillium wilt is a plant disease that commercial growers, farmers, gardeners, and homeowners around the world should recognize. The fungal pathogens that might be involved are Verticillium dahliae and Verti-cillium alboatium. The disease has been called the early dying disease because it causes wilt, branch death, and quick decline of plants. Hundreds of plant species, including trees, shrubs, groundcovers, vines, vegetables, fruits, herbaceous ornamentals, and flowers, can contract this disease. We see symptoms any time from early summer through autumn. The time of infection may depend on the plant species and the geographic location. Research confirms that stressed plants are more susceptible to infection.
This pathogen may be seed- or soilborne and can survive for decades in the soil. Flowing water, strong wind, seed, tools, or machinery can introduce this disease into new geographic locations. It may also be present in apparently healthy plants. The roots of susceptible plants come into contact with soil contaminated with the Verticillium pathogen. The pathogen then enters wounds in roots and grows into the cortex. The fungus produces spores in the roots. These spores are transported systemically upward in the xylem. Spores are then lodged throughout the plant, and new hyphae grow, intensify, and spread farther. Verticillium survives as small resting bodies in diseased plants and eventually returns to the soil.
Symptoms of Verticillium wilt may be restricted to one branch. Although sudden death of the plant is possible, a slow decline over a season or two is more likely. Spore germination and hyphal growth cause a staining of the vascular tissue in streaks. This symptom is characteristic of the disease but not proof of infection. Stained areas can be tested in a lab; the fungus can be successfully isolated from stained tissues.
Symptoms may be acute and include curling, drying, wilting, dieback, or death of foliage. Foliage may be red or yellow between veins. Chronic symptoms such as slow growth, sparse foliage, stunted leaves and twigs, leaf scorch, abnormally heavy seed crops, and dieback can indicate stress caused by the previous year’s infection. Acute and chronic symptoms can affect a plant at the same time. Acute symptoms that occur after more than 1 year of remission indicate a new upward thrust of the disease. If the stem remains alive, Verticillium will grow close to the meristematic regions and allow continuous infection each year.
There is no cure for Verticillium wilt, and it may kill plants. Still, there are many cultural and preventive strategies to manage the disease. Always start with healthy, disease-free seed and avoid susceptible species. Identify and start managing Verticillium wilt as early as possible in established plants. Supply balanced fertilization and provide adequate irrigation to improve the health of the plant. You can help the tree “wall off” the infection. Branches and trees with wilt symptoms should not be removed immediately as they may recover in response to fertilization and watering. Remove dead wood to avoid problems with wood rots and decay. When dead wood is removed, it should be burned, not chipped and reused in the landscape. Because the disease is soilborne, use only resistant species to replace Verticillium-infected plants. At the Plant Clinic, we usually see Verticillium wilt in maple, redbud, smoketree, ash, and catalpa. Some suggestions for replacement plants can be found in RPD no. 1010, Verticillium Wilt Disease. When planting a flower garden, keep in mind that snapdragons, geraniums, and peonies are susceptible, while begonias, hollyhocks, and zinnias are resistant to Verticillium wilt. It is advantageous to control weeds in the landscape because many can serve as a source of inoculum. Dandelions, pigweed, horse nettle, and velvetleaf are all susceptible to Verticillium.