Fusarium wilt (foo-zair-ee-um) is caused by the fungus Fusarium oxysporum f.sp. lycopersici. Fusarium wilt is found worldwide and even resistant tomato varieties may be affected. The fungus is soil-borne and makes its way into the plant through the roots. Once inside, it clogs and blocks the xylem, the tissue that moves water and some nutrients through the plant, preventing water from traveling up the stem and out into the branches and leaves. It may not kill your tomato plants, but they won't be very productive.
Species of Fusarium can infect many plants including potatoes, peppers, eggplants, legumes, and bananas.
Symptoms of Verticillium wilt can be very similar to Fusarium wilt. Verticilliam wilt occurs more often in cooler temperatures while Fusarium thrives in warmer, dry conditions.
What Causes Fusarium Wilt?
The Fusarium wilt pathogen is soil-borne and can remain in the infected soil for years. It can also be carried and transmitted in multiple ways, like:
- infected seed
- seedlings from infected soil
- the bottom of shoes
- shovels and equipment used in infected soil
- infected soil blown into the garden
Ideal conditions for Fusarium wilt include warm, dry weather and acidic soil pH (5.0 - 5.6)
There are tomato varieties that are resistant to fusarium wilt, but if they are weakened by the root-knot nematode, they become more susceptible to it.
Plants infected with Fusarium wilt will be stunted and the earlier they are infected, the more severe the stunting.
Keep reading for more photos and descriptions of Fusarium Wilt symptoms and how to control it.
Symptoms of Fusarium Wilt on Tomatoes
Fusarium wilt can be confused with other wilts, but here are some symptoms to help you identify it in tomatoes:
- Wilting-The plants will literally wilt. Often it starts with a single leaf or shoot, near the top of the plant. It will recover at night when temperatures are cooler, but as it progresses, the entire plant will wilt and not recover. Watering does not make a difference.
- Yellowing- Lower leaves will turn yellow, often starting on only one side. As with the wilting, the yellowing will gradually move up the plant.
- Dry Leaves-The wilted leaves will dry out and fall off.
- Discolored Stem-If you cut open the stem length-wise you will see dark brown streaks.
Management and Control of Fusarium Wilt of Tomatoes
There is no cure for Fusarium and since it persists in the soil for years, it can be very hard to eradicate. Here are some measures to help you control it.
- Resistant Varieties - If you've had problems with Fusarium wilt, choose tomato varieties with resistance. Seed packets and many seedlings will be labeled with their resistance to various diseases. If the tomato variety label includes the letters VFN, for instance, this means the seed or plant is resistant to both verticulum and fusarium wilt and nematodes.
- Sterile Potting Soil - If you are starting your own seedlings, begin with a sterile soilless potting mix.
- Raise the Soil pH - Apply lime to the soil in your garden, to bring the pH up into the neutral range of about 6.5 - 7.0.
- Control Nematodes - Since root-knot nematodes can lessen resistance to Fusarium wilt, don't let nematode populations build up in your soil.
- Don't Cultivate - Avoid injuring plants' roots by not using a hoe or cultivator around your tomato plants. Damaged roots are entry points for the pathogen.
- Disinfect Tools - Clean all tools that may have come in contact with infected soil and make it a habit to regularly clean and disinfect your garden tools.
- Rotate Your Crops - Since the pathogen can persist in the soil for years, you will have to find another area to plant your tomatoes. A five to seven year rotation is recommended, but even that does not guarantee the pathogen will be entirely gone.
- Remove Infected Plants-Even though the disease is soil borne, some of your tomato plants may show better resistance. Pull up the diseased plant and destroy it. Do not compost. This can reduce the chances of disease spread through contaminated tools, gloves and clothing.
You Can Still Grow Tomatoes
If you lose a tomato plant or two to Fusarium wilt, it can be discouraging, but you don't have to give up. on this favorite fruit. Try planting in the spot you grew beans or peas the previous year. Legumes add nitrogen to the soil which will help the tomato plants establish strong root systems. Your best bet for battling plant viruses and blights is to begin with a good root system and a healthy plant.
Try planting your tomatoes in a deep hole. Remove the leaves from the lower two-thirds of the plant and place most of the tomato plant beneath the soil. No matter the planting depth it can still help to remove lower leaves. Rain and overhead watering can cause splash back of contaminated soil onto the leaves and lead to disease spread.
You can also try planting a spring or fall cover crop. While this won't rid the soil of the disease, a cover crop like clover can replace nutrients in the soil and also crowd out weeds that host disease spores.
AVRDC Fact Sheet, UC Pest Management Online