Tomato Diseases: How To Fight Fusarium Wilt

by Matt Gibson

About Fusarium Wilt

Fusarium wilt is known to wipe out entire crops of tomatoes in warmer, southern climates, though it is somewhat limited by lower temperatures in colder, more northern climates. Fusarium wilt is widespread in the southern areas of the United States and Europe, and has been reported in over 30 countries. Fortunately, there are actions that you can take to control and prevent the outbreak of this awful tomato disease.

Causes And Symptoms of Fusarium Wilt

Fusarium oxysporum f.sp. Lycopersici, is the soil-borne fungus that is responsible for fusarium wilt in tomato plants. The fungus can survive indefinitely without any host, but most cases of fusarium wilt are due to infected tomato debris left in the soil from previous harvests.

Symptoms begin with yellowing of the bottom leaves of the tomato plant. The yellowing often stars on one side of the leaf, branch, or shoot, and then slowly spreads out and then upwards, until the entire vine is infected. The vines start to brown along the veins and then begin to wilt as the disease spreads. This wilting is permanent, and often results in a stunted plant. If the plant survives at all, it will be weak, and will produce less than stellar fruit.

Treatment and Control of Fusarium Wilt

There are a few control methods that you can take into practice to help prevent fusarium wilt and a handful of treatment options that can be effective if the infection is caught early enough. As with most fungal infections, it is best to practice control methods to take action against possible infections before they occur. Defend against fusarium wilt and other fungal infections in your garden by following these measures:

• Plant disease-resistant varieties. Disease-resistant plants are not a guaranteed way to avoid fusarium wilt, but they make the possibility of getting the disease much less likely. Look for varieties that are marked with the letter F on the package.
• Use a nitrate-based fertilizer rather than an ammonia-based nitrogen fertilizer. Calcium nitrate, for example, is a good fertilizer to use for your tomato plants. Not only will it provide essential nutrients that your plant needs to survive, and to produce delicious fruits, but it will also help to control the pathogen.
• Even in small gardens, fumigating or steaming the soil can be an incredibly effective treatment. Commercial growers often steam or fumigate their soil with excellent results. However, not every home gardener has the means to undertake such a task. Those that do will not have to worry about fungal infections in the upcoming growing season.
• Alternatively, home gardeners could simply amend their soil to achieve pH levels between 6.5 and 7, which can be similarly effective compared to fumigation or steaming methods.
• A nice, thick layer of mulch will help in multiple ways to fight against fungal growth. A productive layer will keep soil temperatures low enough that fungal spores will have a tough time growing in that environment. Mulching will also help cut down on weeds in the garden beds. Since many weeds can be hosts for fusarium wilt and other fungal diseases, mulching to help with weed maintenance is a win-win scenario.
• Crop rotation is one of the most important things you can do to prevent fusarium wilt and a wide array of other tomato diseases. Don’t plant tomatoes in the same spot more than once every four years. This won’t completely eliminate the possibility of a disease, but it will surely reduce the chances of serious infections in your garden.
• Clean garden practices can go a long way in disease prevention, especially in the case of bacterial or fungal diseases. As inoculum, and other diseases can be spread through infected items and body parts, such as stakes, soil, gardening tools and equipment, shoes, seeds, clothing, and even gardener’s hands, keeping your gardening area nice and tidy can go a long way towards preventing infection. This is especially important when starting seeds or seedlings, as you should always provide a fungus-free, sterile environment for new plants.

Common Questions and Answers About Fusarium Wilt

Can you eat tomatoes with fusarium wilt?

Fusarium wilt cannot infect humans, so it is safe to eat tomatoes that have fusarium wilt. In fact, tomatoes with fusarium wilt may be sweeter than uninfected fruit due to reduced water flow to the tissue. However, ripened fruit with fusarium wilt is especially susceptible to rot, so it will need to be harvested quickly. Often, progression of the disease will prevent green, immature tomatoes from ever ripening.

How do you stop fusarium wilt?

As there is no cure for fusarium wilt, infected plants must be removed from the garden and destroyed. The most effective way to stop fusarium wilt is to grow resistant plant varieties. You can find plants that are resistant to race 1 and race 2 of fusarium wilt. Resistant varieties will be labeled with an “F” on seed packets or plant labels. However, even these resistant varieties may show symptoms if infections are severe. Gardeners should treat seeds with fungicide or heat before sowing them. But are also steps gardeners can take to fight fusarium wilt even if crops have already been planted.

Rotate tomato plants to another part of the garden, or grow them in containers, being careful not to use infected soil. Sterilize all gardening supplies, equipment, tools, gloves, and clothing after each time you work in the garden and when moving from one area or plant to another. Gardeners can opt for sterile soil-free planting mediums. Ensure sufficient drainage in planting areas, avoiding wet spots. If your property doesn’t offer sufficient drainage, consider building raised beds to grow your plants in. Select a nitrate-based nitrogen fertilizer, like calcium nitrate, instead of ammonia-based fertilizers, or add lime to soil.

Commercial farmers sometimes fight fusarium wilt by steaming or fumigating their soil, but home gardeners can get equivalent effects by raising the pH level of soil to between 6.5 and 7.0. (If you aren’t sure of your soil’s pH level, this article explains how to test pH levels in soil.) Applying a thick layer of mulch will help to keep the temperature of garden soil low, slowing the growth of the fungus. Gardeners should be vigilant about weeding in areas with fusarium wilt, as weed plants can act as hosts for the fungus.

How does fusarium wilt spread?

Fusarium wilt is a soilborne fungal disease that spreads in soil, entering plants individually via their root systems. It can also spread when transplants are introduced to the garden, through the coat of infected seeds, or the fungus can hitch a ride on gardening tools, equipment, supplies, gloves, or clothing used around infected soil or plants. High air and soil temperatures assist in the spread of the disease. Fusarium wilt does not spread from plant to plant above the ground. It can survive indefinitely without a host.

Is fusarium wilt contagious?

Fusarium wilt is contagious and enters plants through the root system. It is a soilborne fungal infection that can live in soil for many years, even after infected plants are removed. In addition to being transmitted through soil, fusarium wilt also spreads via new transplants coming into the garden and on gardening tools, equipment, supplies, gloves, and clothing. Fusarium wilt can survive indefinitely even without a host, so gardeners must take action against it if their plants are infected.

What are the symptoms of fusarium wilt?

Fusarium wilt causes discoloration of foliage to yellow or brown as well as wilting that improves slightly at night. It makes its first appearance as fruit begins to mature, with lower leaves turning yellow. This yellowing may initially be limited to one side of a branch or plant. Next, leaves and stems will begin to wilt. If you split an infected stem open lengthwise, you’ll notice the vascular tissue (closest to the outside) has turned brown, though the pith in the center of the stem is healthy. As a result of fusarium wilt, plants may be stunted, and young seedlings may die.

What causes fusarium wilt in tomatoes?

Fusarium wilt is a disease caused by the fungus Fusarium oxysporum f.sp. Lycopersici,. Tomatoes and other plants contract fusarium wilt through their root systems. High air and soil temperatures as well as splashing water aid in the spread of fusarium wilt. The fungus is soilborne and, in addition to spreading via infected soil, it can enter a garden when new transplants are brought in, if infected plant debris is left in the soil, and on gardening tools, equipment, supplies, gloves, and clothing exposed to the fungus. Once fusarium wilt enters a plant, it plugs tissue and reduces the plant’s ability to move water through its cells. Fusarium wilt can survive indefinitely without a host plant, so management is crucial.

What does fusarium wilt look like?

Fusarium wilt begins as yellowing or browning of foliage in one area (sometimes just one side of a branch or plant) that spread and causes wilting. If you open an infected stem by splitting it lengthwise, you can see the discoloration of the plant’s vascular tissue (nearest the outside) to brown), with the pith in the center of the stem remaining healthy. Mature or young plants may have stunted growth, and seedlings may die as a consequence of fusarium wilt.

Did fusarium wilt ruin your tomato crops? We are looking for photos. If you think fusarium wilt damaged your plants, snap a picture and send our way.

Want to learn more about fusarium wilt on tomatoes?

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