Wilted leaves on plants don't always hint at dry soil. If your plants wilt even when the soil is moist, look for another cause. Infecting some plants, an insidious fungal disease called verticillium wilt starts -- literally -- from the ground up.
Plants infected with verticillium wilt typically show a progression of symptoms: The leaves -- particularly the lower leaves -- first turn yellow, then wilt and finally die. Sometimes the dead and dying leaves drop from a plant, and other times they remain attached even after they're dead.
Some plants, however, show different symptoms:
- Slow growth.
- Sudden wilting.
- Only one side of a plant (or a single branch) wilts and dies.
- Reddish-brown or grayish-black streaks inside the stems of trees and shrubs.
- Dead, elongated areas of bark on infected limbs or trunks.
The Root of the Problem
Two fungal species -- Verticillium dahliae and Verticillium albo-atrum -- are the culprits. These pathogens live in the soil and penetrate a plant's root system. The fungus worms its way into a plant's vascular system and invades the xylem, which manages the internal transport of water and minerals. As the fungus grows, it plugs the xylem channels, preventing water from reaching the leaves. When their water supply is cut off, the leaves and branches wilt and die.
Using fungicides or other chemicals rarely controls verticillium wilt. This makes prevention the best course of action to head off disease before it takes hold. Use an integrated pest management strategy with these tips in mind:
- Remove dead or diseased branches promptly.
- Avoid using high-nitrogen fertilizers; fertilize plants only according to soil-test recommendations.
- Use herbicides judiciously and only as spot-treatment controls.
- Choose plants for your yard that are immune or resistant to verticillium wilt instead of others with proven weaknesses.
Sanitize pruning tools by soaking the blades for five minutes in a solution of 1 part household pine-oil cleaner and 3 parts water. Rinse the tools or let them air-dry before using them. Although it's time-consuming, sanitize the blades between each cut on diseased plants.
Dispose of all dropped leaves and pruned branches from diseased plants. Don't add them to the compost pile, and don't use chipped branches as mulch.
Many types of plants are more susceptible to verticillium wilt than other plants, such as:
- Redbud (Cercis canadensis), hardy in U.S. Department of Agriculture plant hardiness zones 4 through 9.
- Pin oak (Quercus palustris), USDA zones 5 through 7.
- Weeping fig (Ficus benjamina), USDA zones 10 through 12.
- Indian hawthorn (Rhaphiolepis indica), USDA zones 8 through 11.
- Heavenly bamboo (Nandina domestica), USDA zones 6 through 9.
- Mealycup sage (Salvia farinacea), USDA zones 8 through 10.
- Transvaal daisy (Gerbera jamesonii), USDA zones 8 through 10.
- Tomato (Lycopersicon esculentum), potato (Solanum tuberosum), pepper (Capsicum spp.) and eggplant (Solanum melongena) -- all members of the Solanaceae plant family.
- Garden balsam (Impatiens balsamina).