Verticillium wilt is a soil-borne fungus that can damage a tomato garden, especially during periods of cool weather or rain. Because it affects the vascular system of the plant, it can cause myriad symptoms, including dropped and yellowing leaves, deformed or misshapen fruit, stunted growth or plant death.
Verticillium wilt is most commonly found in regions that feature extended periods of cool weather such as the northeastern United States. Because the fungus spores can overwinter, both in the soil and in improperly discarded affected plants, it can be difficult to completely eradicate. However, the problem can be adequately managed by employing good sanitary practices, combining crop rotation and only planting verticillium wilt-resistant tomato varieties.
Verticullium wilt in tomato plants is caused by verticillium albo-atrum. This fungi can be found in infected soil and can survive there for many seasons. Using tomato plants as their hosts, the fungus enters through the roots and causes damage to the entire vascular system of the plant. Seedlings and young plants might wither and die very quickly, whereas mature, fully established plants might exhibit stunted growth, considerably diminished yields and overt signs of illness including yellowing, dropped leaves, upturned, curled leaves and discolored patches.
Signs and Symptoms
One of the earliest indications of verticillium wilt in tomatoes is rapidly yellowing, drooping leaves that curl, often along only one side of the tomato plant. The damaged leaves are an indication of vascular damage to the plant, and usually the leaves of a tomato plant with verticillium wilt will simply drop right off of the plant. In a relatively short period of time, dark lines form along both the interior and exterior of the stems, and the entire plant will start to wilt. In many instances, discoloration and patches that resemble cankers will also begin to appear.
Management and Control
Managing verticillium wilt can be difficult because it is a soil-borne fungus. However, in most cases it can be contained and managed by removing affected tomato plants immediately and practicing crop rotation to reduce instances of recurrences. Practicing good sanitation including weed removal can also be beneficial. It's important to avoid over-watering which can exacerbate a verticillium wilt problem.
The best defense against verticillium wilt in tomatoes is to select resistant varieties of tomatoes to plant. Seed catalogs mark resistant strains with the letter "V" beside the variety. If you purchase tomato seedlings from a garden center or plant nursery, ask about tomato varieties that are impervious to verticillium wilt. Closely examine plants for any signs or indications of illness on the leaves or stems including yellowing leaves, discolorations, cankers and dark lines on the stems.