The fungus Fusarium oxysporum f. sp. lycopersici
Tomato, eggplant and pepper. Can also survive on weeds such as pigweed, mallow, and crabgrass.
Signs and symptoms
- Initially, plants wilt during the hottest part of the day and recover at night.
- Leaflets turn yellow on one side of the plant, or even just leaflets on one half of a compound leaf.
- The entire plant soon turns yellow and wilts. Browning of leaves occurs rarely.
- Peel the epidermis off the lower stem to see dark red brown discolored vascular tissue.
- Confirm diagnosis by sending a plant sample to the University of Minnesota Plant Diagnostic Clinic, as this disease is easily confused with Verticillium wilt.
- Disease of warmer weather (optimal soil temp 82°F)
- More severe in acidic soil
Biology and disease cycle
- The fungus can survive as chlamydospores (fungal resting structure) for many years in the soil or in plant debris.
- Can be seed borne, but rare in commercial seed.
- The fungus can be introduced on infected transplants or spread on equipment contaminated with infested soil.
- Long distance dispersal by air borne spores only occurs very rarely.
- The pathogen most often enters through root wounds caused by cultivation or by nematode feeding.
- The pathogen moves up the plant through the vascular system.
- Only one infection cycle occurs each growing season; once a plant is infected, it usually will not spread to another plant in the same growing season.
There are many varieties with resistance to Fusarium wilt. Fusarium oxysporum f. sp. lycopersici has three races; race 1, race 2, and race 3. Some tomato varieties may be resistant to one race, yet completely susceptible to another. Most seed catalogues indicate resistance to Fusarium and which of the 3 races the variety is resistant to.
Varieties without resistance can be grafted onto disease resistant root stock.
The fungal pathogen may be present in resistant plants even if they do not show any symptoms. For this reason, planting resistant varieties should not be considered a rotation away from susceptible tomatoes.
- Purchase disease free seed and transplants from a reliable supplier.
- Clean soil and plant debris off all equipment prior to moving to a new field.
- Completely remove infected plants. Burn or bury plants in an area that will not be used for solanaceous crops.
- Rotation away from susceptible crops for 3-5+ years will reduce disease, but careful weed management must be done during this period.
- Avoid excessive N as it will encourage disease.
- Use of calcium nitrate fertilizer instead of ammonium nitrate can reduce Fusarium disease severity in some soils.
- In acidic soils, raising the soil pH to 7 can help to control disease.
There are currently no pesticides that provide control of Fusarium wilt.