Fusarium wilt of tomato is caused by the soilborne fungus Fusarium oxysporum f. sp. lycopersici.
Fusarium oxysporum f. sp. lycopersici mainly causes wilt on tomatoes, but it can infect many other plants including potatoes, peppers, eggplants, and legumes. Strains of the pathogen that can overcome host resistance are divided into three main races currently known as: race 1, race 2, and race 3. There are resistant varieties available for each race. However, varieties may have resistance to one race while being susceptible to infection by the other two.
Symptoms and Signs
Initially, symptoms of Fusarium wilt of tomato appear as one-sided wilting of only half of the plant, branch, or leaflet. At first, the plant will appear to recover from the wilt, but as the disease progresses, it will become permanent regardless of temperature or water status. Lower leaves will become yellow first before chlorosis spreads to the higher branches, eventually leading to defoliation. Plant growth is typically stunted and few to no fruit develop. If the stem is cut open near the base of the plant, longitudinal light brown streaks can be seen within the vascular tissue (center of the inner stem). This discoloration can be slight and difficult to observe.
Look alike diseases. Other diseases that cause tomatoes to wilt include southern blight, bacterial wilt, and Verticillium wilt. However, the one-sided wilt or yellowing of the plant, leaf, and leaflet mentioned above are distinctive of Fusarium wilt.
Fusarium wilt is caused by a soilborne fungus that is able to survive in the soil without a host for up to ten years. Ideal conditions include warm soil temperatures, acidic soil pH (5.0 - 5.5), and high humidity. Due to the environmental conditions required for disease development, symptoms of infection may not appear until the mid to late growing season. The fungus is able to enter through the roots and colonize the vascular tissue (water and nutrient conducting vessels) which allows it to spread throughout the plant. The blockages in the vascular tissue created by the pathogen cause the yellowing, wilting, and eventual death of above ground plant parts. The fungus is able to produce chlamydospores (fungal resting structures) that can survive in the soil or plant debris for years.
General Disease Management
Fusarium wilt can be difficult to manage once it is introduced and there is no known cure once it has become established within an area. However, there are preventative and disease reduction measures that can be implemented:
- Select resistant varieties. For fields with a history of Fusarium wilt, planting resistant varieties of tomato will inhibit severe symptoms. See the Southeastern US Vegetable Crop Handbook for a list of varieties with resistance. Seek guidance from a specialist to help identify which race is present in your field.
- Use grafted tomatoes. Tomato rootstocks that are resistant to Fusarium wilt are available and can be used with a susceptible scion variety. See vegetablegrafting.org for more information.
- Crop rotations for 3-5 years. Rotating away from tomato crops will reduce inoculum (spores) in the soil. This will not guarantee the elimination of disease, but will reduce the severity and incidence of infection on the subsequent crop. Weeds, such as pigweed, mallow, and crabgrass, can be hosts for the Fusarium wilt pathogen, so frequent maintenance of the infested area is necessary during this period of time.
- Only plant healthy transplants. Closely inspect transplants for symptoms of disease before planting to decrease the likelihood of introducing disease.
- Wash tractors and equipment between fields. Infested soil can be carried to other fields on equipment and tools. Frequent cleaning is highly recommended, particularly if moving from an infested field to a clean field.
- Use sterile potting media. If you are starting your own seedlings, use of a sterile soilless potting media is suggested to minimize the chance of introduction of the disease.
- Manage soil pH. Raising soil pH to a neutral range (6.5 - 7.0) by using lime will reduce the persistence of the pathogen.
- Avoid excessive nitrogen. High levels of nitrogen and low levels of potassium in the soil can increase a plant’s susceptibility to Fusarium wilt. Avoid over-application of high nitrogen fertilizers and use a soil test to determine nutrient levels.
Disease Management for Conventional Growers
Conventional growers should implement the practices mentioned in the General Disease Management section. Additionally, conventional growers may fumigate the soil to reduce populations of the pathogen. See the Southeastern US Vegetable Crop Handbook for more information on soil fumigation. Miravis Prime (pydiflumetofen + fludioxinil; FRAC 7 + 12) is the only fungicide available for controlling Fusarium wilt of tomato. Any fungicide application must be made before disease is present to increase likelihood of effectiveness. However, crop rotation and host resistance are the most effective disease management options.
Disease Management for Organic Growers
There are several organic products labeled for Fusarium wilt of tomato, but efficacy is not consistent. It's important to follow all preventative practices listed in the General Disease Management section before relying on an organic product to effectively manage Fusarium wilt.
Disease Management for Homeowners
Homeowners can manage Fusarium wilt by rotating crops every 3-5 years. If Fusarium wilt pressure is high, homeowners can consider installing raised beds with clean soil, as well as switch to planting a variety with resistance. There are no homeowner fungicides that will manage Fusarium wilt.
- The NCSU Plant Disease and Insect Clinic provides diagnostics and control recommendations.
- The NC State Extension Plant Pathology portal provides information on crop disease management.
- The Southeastern US Vegetable Crop Handbook provides information on vegetable disease management.
Publication date: June 22, 2021
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