Fusarium Wilt
Disease · Commonly affects: Tomato, Watermelon, Muskmelon (cantaloupe), Pea, Spinach, Basil
Fusarium wilt is a soilborne fungal disease caused by Fusarium oxysporum, which lives in the soil and enters plants through the roots. It matters to gardeners because each host-specific strain clogs a plant's water-carrying tissue, killing susceptible crops, and the fungus can survive in the soil for many years once a bed is infested.
How to identify it
The first sign is usually yellowing of the older, lower leaves, often on just one side of the plant or one branch while the rest still looks green. Plants wilt during the heat of the day and may perk up overnight early on, but they decline steadily as the disease spreads. A reliable clue is brown streaking in the water-conducting tissue just under the outer skin of the stem, which you can see by slicing a lower stem lengthwise.
Damage
The fungus grows into and plugs the xylem, the vessels that carry water up from the roots, so leaves droop, yellow, and dry even when the soil is plenty moist. Infected plants become stunted, set little or no fruit, and usually collapse and die before the end of the season.
Prevention
Plant resistant varieties whenever they exist; on tomatoes, look for an F (or FF for two races) on the seed packet or transplant label, which flags built-in Fusarium resistance. Rotate susceptible crops out of an infested bed for several years, keep beds well drained and avoid overly wet soil, and give plants full spacing so roots and foliage stay vigorous. Start with clean, healthy transplants, and clear out and dispose of crop debris at season's end instead of tilling it back into the soil.
How to manage it
There is no cure for a plant once it is infected, so pull affected plants roots and all, bag them, and put them in the trash rather than the compost pile so the fungus does not build up. Knock soil off tools and wash your hands between working on diseased and healthy plants to avoid carrying spores, and water steadily at the soil line to keep roots from drying out and adding stress. Where the disease is already established, covering moist soil with clear plastic through the hottest weeks of summer (soil solarization) can reduce fungal populations near the surface, and grafting susceptible tomatoes onto resistant rootstock can cut losses in future plantings.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.