Tomato Diseases: How To Fight Anthracnose

by Matt Gibson

About Anthracnose

Finding out that your tomato crops are infected with tomato anthracnose can be incredibly discouraging. You may notice ugly legions and large rotten areas and realize that you have noticed the infection a bit too late in the game to save your plants. Untreated anthracnose can cause a whole lot of damage and destroy an entire crop turning a beautiful looking group of plants into a crop of rotten fruit in just a few short days.

It is extra important when dealing with anthracnose, to catch the infection as early as possible, because like many fungal diseases, anthracnose is tough to treat once the infection has taken hold, but the damage can still be minimized if you catch it early enough. Vigilant scouting is essential, if you want to catch the disease before it’s too late. 

Causes And Symptoms of Anthracnose

If the soil that you are growing your tomatoes in has inadequate drainage, you are providing an environment that is more susceptible to the bacteria that is responsible for anthracnose. Colletotrichum bacteria is known to attack the tomato plant’s fruit during every stage in its growth, and it is especially fond of soggy soil. The bacteria can be spread by wind, birds, and insects, which infect the soil with the bacteria, initiating the disease.

Once the anthracnose fungus is present in the soil, it can be splashed onto the plant with irrigation or rain water, or attach itself to the fruit if/when it touches the ground. The roots of the plant can also be attacked, especially in a greenhouse, as the warmer temperatures and aerial watering systems help the fungus stay active in the soil. Any small lesion in the root system, which could easily be caused by garden pests like the flea beetle, provides an easy access point for the disease to enter and begin to colonize within the plant.

If the colonization occurs when the plant has green fruit, you will not be able to see the infection until the fruit starts to ripen. Once the tomatoes start to become ripe, the symptoms of anthracnose start to become more noticeable. Small, slightly sunken, wet-looking spots or abrasions will appear. The lesions quickly get larger and the depressions become more pronounced as the disease progresses. The center of the tomato begins to darken, and you will notice the emergence of many small, fungal structures. A semisoft decay begins to occur as the fungus spreads, eventually leading to large rotten areas. Once the disease has reached this stage, there is no saving the harvest.

Treatment and Control of Anthracnose

Once anthracnose has had a chance to spread and progress, gardeners are left with a big mess to clean up, instead of a big harvest to reap. This can be quite disheartening. The best way to avoid the devastation of your tomato plants, is to prevent anthracnose, and other tomato diseases from occurring in the first place. The best way to keep anthracnose out of your tomato garden, is to practice cultural control methods, which minimize the chances of soil infections such as anthracnose.

Annual crop rotation is one of the best ways to fight soil-borne fungal infections. Make certain that no non-solanaceous plants like peppers, soybeans, and potatoes were planted in the soil  that you are about to grow your tomatoes in within the past year. Continue to rotate out where you grow your non-solanaceous plants, putting two to three years (if possible) between each crop.

Using only certified, disease-free seeds will really help avoid fungal issues as well. If disease-free seeds are not available, soak the seeds in hot water for 25 minutes before planting to kill any bacteria that might be growing or living inside the seeds you are about to sow. Oftentimes, it is through the seeds, or transplants themselves, that the fungal spores of anthracnose and other diseases are able to enter your garden. 

Another good cultural control practice is to lay out a thick layer of mulch around the base of each tomato plant. Mulching will help direct the water into the soil and away from the above ground parts of the tomato plant. Mulch will also act as a barrier between the plant and the soil itself, which will cut down on the possibility of spores splashing onto the plant due to rain or irrigation. 

Once an infection has been noticed, it is of vital importance to remove all infected fruit from the vine and discard it properly. Plants that survive the infection can be treated with fungicide sprays that can be highly effective. The best fungicides on the market for tomato diseases contain potassium bicarbonate, which is safe to use on food products, and is considered safe by the FDA.

The most commonly used fungicide for anthracnose is sodium bicarbonate, or baking soda. This organic treatment can be used for both prevention and treatment. If your plants are showing signs of powdery mildew, hit them with a blast from the water hose on the infected areas to dislodge and knock loose as many mold spores as possible.

Fungicides used to fight septoria leaf blight will also work for protecting fruit against anthracnose. Also, fungicides that are copper based have been successful in treating anthracnose.

Common Questions and Answers About Anthracnose

Can anthracnose kill trees?

As a rule, anthracnose does not kill trees. However, repeated infections with anthracnose can make trees weaker and more likely to die as a result of other issues. Anthracnose may cause leaf drop, but those leaves will be replaced with new growth once the weather warms up. Cankers may also develop as a result of anthracnose, which can kill individual branches due to girdling. Cankers may also result in the death of buds and twigs. During the tree’s dormancy, anthracnose can kill its bark and cambial tissue. (Cambial tissue, or cambium, is the layer between the bark and wood that produces secondary growth of stems and roots.)

Can you eat tomatoes with anthracnose?

As long as you cut out the infected area of the tomato, it is safe to eat tomatoes infected with anthracnose. Be sure to throw away the infected area, as it contains the spores that cause anthracnose and can spread the disease.

Does anthracnose stay in soil?

Anthracnose is a soilborne disease, and the spores that cause anthracnose live in infected soil. The fungi that cause anthracnose also survive the winter on infected plant debris on the ground, such as infected buds, leaves, twigs, and fruiting structures. In infected trees, the anthracnose spores overwinter in dead twigs and the margins of its cankers. Anthracnose spores can live in soil for three to nine months, even without an infected plant nearby. In the soil, spores travel and spread through the movement of water, such as morning dew, runoff, irrigation, or rainfall.

That’s why it’s important to clean up and dispose of plant debris near affected plants as one of the main ways to fight anthracnose. Do not discard infected debris or soil in your compost pile; it should be dried and burned. Your compost may not reach temperatures high enough to kill the anthracnose spores, and you’ll risk spreading the disease further. It’s also important to wash your clothing, garden tools, and gardening gloves, as anthracnose can live for up to six weeks on these items.

Does neem oil kill anthracnose?

Yes, neem oil is a common remedy gardeners use to fight against anthracnose. You can make a homemade neem oil spray treatment by mixing four or five drops of dish soap and one teaspoon of neem oil into a liter of warm water.

How do you treat anthracnose on tomatoes?

Treating anthracnose is a multi-step process. First, remove any infected plants from your garden, then destroy them. Do not add them to your compost heap, as you risk reinfecting plants when the compost is used. Also bag and remove any plant debris or fallen leaves underneath or surrounding the infected plants, then dry and burn this material. Then apply a fungicide of your choice. Sulfur dust fungicide and liquid copper fungicide are both good choices.

Do not replace plants in the spots where infected plants were removed, as anthracnose may still be lurking in the soil. Mulch the surface of the soil around your remaining plants to provide a barrier between any spores that may be in the soil and your plants. This barrier is meant to prevent anthracnose spores from spreading from soil to plants via splashing rainfall or irrigation. Be careful not to let mulch touch your plants; leave a space between the stem or trunk of each plant and the mulch you lay down.

Cultural controls and preventive measures should be called on to make sure anthracnose does not return after it’s been removed from the garden. Water plants in the morning to give them plenty of time to dry out before the cooler temperatures at night. Make sure plants are buried to the appropriate depth so leaves are not directly touching the soil. You can also utilize staking [https://www.gardeningchannel.com/staking-your-garden-plants-guide/] or place cages around your plants to prevent them from coming in contact with potentially infected soil. After each time you work in your garden, clean and sterilize tools, equipment, gardening gloves, and the clothes you wore to work to prevent spreading anthracnose. Anthracnose spores can live on garden tools or clothing for up to six weeks.

Is anthracnose harmful to humans?

Anthracnose cannot infect humans or cause symptoms in humans.

What are the symptoms of anthracnose?

Symptoms of anthracnose begin with small discolored spots on leaves, which may be yellow, brown, dark brown, or black. These spots spread and expand until they can eventually cover an entire area, with the color darkening as time goes on. Cankers may appear on stems or on the stalks that join leaves to stems (called petioles), with leaves dropping and fruit rotting where cankers appear. Roots may also show rotting, which is called black dot root rot. Infected fruit can be identified by waterlogged circular spots that create sunken areas up to half an inch across. Eventually, these spots turn black in the center and release masses of spores, which range in color from pink to orange and have a texture like gelatin.

What causes anthracnose?

Anthracnose is a fruit rot disease caused by various species of fungi including Apiognomonia errabunda, A. veneta, Colletotrichum gloeosporioides, Discula fraxinea, the Glomerella species, the Gnomonia species, some Marssonina species, and Stegophora ulmea. The spores live on infected plants, plant debris on the ground, and in soil, and it can also be seedborne. Water helps spread the spores via irrigation, morning dew, rainfall, and runoff. Anthracnose is also spread through wind, insects, and gardening tools, equipment, and clothing exposed to the spores. It’s most likely during periods of cool, wet weather and high humidity.

There are also factors that make anthracnose infection more likely or help it along, which gardeners can address via cultural controls and preventive measures. Ensure plenty of air circulation between plants by providing proper spacing and staking tall plants. Add a layer of mulch to provide a barrier between spores that may be lurking in the soil and plants, being careful not to let the mulch touch plants directly. Avoid overhead irrigation systems or watering from overhead, as the water that splashes onto foliage can help spread anthracnose. Instead, use drip irrigation or water the base of plants.

Make sure that soil is well-draining, and amend it with compost to give plants the nutrition they need to grow strong and healthy and fight disease. Avoid allowing fruit to touch the soil. Rotate plants every two or three years. Pick fruit as soon as it ripens to lessen the chance of anthracnose developing. Do not save seeds from your plants in a season when you’ve struggled with anthracnose. Try not to work in the garden when the fields are wet, and always disinfect gardening tools and equipment as well as clothing and gloves when your work is complete. Gardeners can also opt for plant varieties that are resistant to anthracnose.

What does anthracnose affect?

Anthracnose infects crops such as bananas, cereal, corn, cotton, curcubits, mango, onions, peppers, sorghum, and tomatoes. Anthracnose can also infect shade trees, with ash, oak, maple, white oak, walnut, and sycamore being particularly susceptible, along with grasses and annuals.

What does anthracnose look like?

Anthracnose starts out as small discolored lesions on foliage, ranging in color from yellow to brown, dark brown, and black. The spots expand as the disease spreads to eventually cover whole areas of the plant, turning darker as they mature. Anthracnose also causes cankers on stems or leaf stalks that can cause rotting fruit or result in leaf drop. Roots may show black dot root rot. Fruit infected with anthracnose exhibits watery circular sunken areas up to half an inch wide that eventually turn black in the middle and release fungal spores, which are gelatinous and range in color from orange to pink.

If you have spotted tomato anthracnose in your garden, send us pictures!

Want to learn more about Anthracnose on tomatoes?

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