19 Tomato Diseases: How to Identify, Treat, and Prevent Them

The first signs of early blight are tiny dark brown spots on the lower foliage of a plant. As the spots grow, they typically get a ring of yellow around the spot, giving a target-like appearance. The infection can spread quickly and begin causing leaves to turn yellow and brown, then fall off. You may also notice dried, dead leaves clinging to the stem.

While resistant tomato varieties are available, the key to preventing early blight is to improve airflow, reduce splashing or moisture on the leaves, and ensure that you practice proper crop sanitation. This means spacing tomatoes farther apart (often 24-36” depending on variety and your trellis) and regularly pruning off lower leaves.

Avoid overhead irrigation, instead opting for drip irrigation or soaker hoses that deliver water straight to the root zone. Lastly, thoroughly remove and dispose of tomato debris at the end of the season. Leftover tomato debris from the previous crop is the most common source of disease. It can also spread by infected seeds or transplants.

If early blight has already taken hold of your tomatoes, you have a few options. First, carefully remove infected parts and dispose of them. Avoid doing this in windy or wet conditions because spores can easily spread. Be sure to wash your hands and sanitize your pruners after doing so.

Next, you can apply a diluted neem solution to help treat and prevent further spread. An organic copper fungicide or baking soda spray (1 tbsp. baking soda, 1 tsp. vegetable oil, and 1 tsp. mild soap in a gallon of water) can also help stop the disease).

First, the leaves looked like they’re soaked in water. Then, spots begin to enlarge into purple-colored oily blotches. You may notice outer rings of gray-white fuzzy on the underside of the leaves (this is the mycelia). Entire leaves and petioles will begin to die off. Fruits can also get infected by turning brown around the “shoulders” of the tomatoes.

At high humidity and moderate temperatures (60-75°F), late blight can take hold in as little as 10 hours. You have to ruthlessly remove any slightly infected plants and get them off the property. Be sure that all crop debris from previous nightshade-family crops is completely removed from the garden at the end of every season. Choose blight-resistant varieties in the future.

Late blight is a tough one to beat because it spreads so rapidly. There is no real cure, but you can stop spread with preventative fungicides like copper, sulfur, or the safest option: neem oil.

The bottom ends of fruits (where the flower once was) look black, greyish, or sunken-in as if they are rotten.

Consistent watering and proper calcium levels are the most important factors for preventing this problem. Use a soil test and, if necessary, amend with lime, bone meal, or eggshells. Ensure that plants are not heat or water stressed.

Once a fruit has begun to rot at the end, it is irreversible. Remove the affected tomatoes and try to fix the root cause to save future yields.

Gray mold typically begins by covering tomato flowers and young fruit. It looks like circular white spots that later turn yellow.

Always avoid overhead irrigation with tomatoes. If you live in a moist climate, create more air circulation by increasing the spacing and pruning of your plants.

In the case of severe gray mold infections, remove all infected leaves or fruit. Sanitize your hands and pruners. Apply a neem oil, a horsetail (Equisetem) spray, or a diluted fungicide to kill any spores and prevent more infection.

Powdery mildew looks like a gray or white flour has been sprinkled on your tomato leaves. Circles of dead tissue may be surrounded by a yellow halo.

Resistant varieties (labeled “PM” in seed catalogues) tend to be the easiest means of prevention. You should also focus on cultural controls like cleaning up crop debris, removing pruning, maintaining airflow, and avoiding overhead irrigation.

The biofungicide Bacillus pumilus is one of the safest and most effective sprays for powdery mildew. However, most gardeners remove infected foliage, prune more leaves, and then apply a diluted neem solution before resorting to fungicide applications.

Infected yellowing leaves rapidly wilt, no matter how much water they receive. The most notable characteristic of this particular disease is the “yellow flag effect” where only one side of the plant wilts, while the other remains green and normal.

The best prevention is growing resistant varieties (labeled “F”, “FF”, or “FW” in seed catalogues). Some of our favorites are ‘Big Beef Plus’, ‘Sun Gold’, Better Boy’, ‘Beefmaster’, or ‘Early Girl’.

You also want to control root knot nematodes in your tomato patch, as they can damage the roots and cause plants to be more susceptible. Certain companion plants for tomatoes (such as white mustards and marigolds) can help suppress nematodes.

Unfortunately, fusarium wilt is incurable. It can become permanent and live in the soil for decades. You can suppress the spread by removing infected plants and some volume of the infected garden soil. Always clean and sanitize garden tools and boots after dealing with this pathogen.

Fusarium root rot attacks the roots of young or weak plants, causing wilting and stunting. Above-ground, the oldest leaves begin to show symptoms first. They start to turn yellow along the edges and rapidly die.

Maintain properly aerated, well-drained soil by adding plenty of organic matter, regularly broadforking, and avoiding tillage. Don’t overwater tomatoes. Choose resistant varieties (labeled “FOR” in catalogues), including ‘Supersweet 100’, ‘Cherry Bomb’, ‘Sakura’, or ‘New Girl’.

There are no known controls for this disease. Prevention and sterilization practices are key.

In warm and humid weather, you will notice black velvety lesions on tomato fruits. These will grow into circular, sunken lesions that decay ripe fruits.

The easiest means of prevention is to simply harvest your tomato fruits just before they fully ripen (especially if rain is on the way). Always avoid overhead irrigation, particularly during the late summer. Try to keep fruit as dry as possible.

You should also try to protect fruits from sun scald by keeping them shaded beneath leaves. Remove dead or infected parts out of the garden.

In rainy years, both organic sprays (like neem) and conventional fungicides (like calcium chloride) may be necessary to kill Black Mold. However, you will have to thoroughly wash fruits before consuming. It is much easier to harvest them a little earlier and ripen near bananas in your kitchen.

A mosaic-like pattern on tomato leaves is the characteristic symptom. The leaves may become deformed, curled, and fern-like.

Never smoke or use tobacco products near your tomato plants. Choose resistant cultivars (labeled “TMV”) and always source from a reputable disease-tested seed company.

There is no way to treat TMV.

Young leaves turn bronze and then accumulate dead spots on the surface. Ripened tomatoes can also show symptoms of blotchy yellow spots with rings on the outside (it’s safe to cut them off and still eat the fruit).

Controlling thrips is actually the secret to keeping this virus at bay. Try interplanting with aromatic tomato companions that repel pests and attract predatory insects.

You can also opt for resistant cultivars like ‘Summerpick’, ‘Big Beef Plus’, ‘Plum Regal’, or ‘Red Defender’.

There is no known control. Practice crop rotation to try to avoid re-contamination.

Yellowing leaves with mottled, mosaic-like patterns are the primary symptom. There may also be concentric rings of dead spots on fruit.

Avoid planting tomatoes near alfalfa. Plant beneficial companions to keep aphid populations in check. One experimental prevention strategy is to use reflective silver mulch below the tomato planting to help repel aphids and stop spread. This can have mixed results, but it’s worth a shot if you’re in alfalfa-country.

There are no known chemical controls. Getting rid of aphids may help lessen the spread.

Bacterial spots can occur on all above-ground plant spots. First, leaves may have water-soaked circular lesions. The spots start out green or yellow, then darken to reddish-brown. As it progresses, severe leaf yellowing and death occurs. On fruit, spots may look like raised blisters with a yellow halo.

Preventing this bacterial disease is all about sourcing pathogen-free seeds and transplants. Keep tomato leaves dry and avoid handling them when wet. Sanitize your tools and hands after touching potentially infected areas. Practice crop rotation and always burn or dispose of tomato debris.

Plants with bacterial leaf spot can’t be cured, but you can try to stop the spread with copper or neem applications. Avoid eating infected fruit.

As the name implies, rapid sudden wilting and yellowing of leaves are the main symptoms of bacterial wilt in tomatoes. To decipher it from other wilt-causing pathogens, look in the inside stems of infected plants. Take a clean, cut section of the diseased stem and place it in clear water. It will appear brown and decaying, with a milky slime of bacterial cells streaming into the water.

Removing and destroying infected plants is an important means of prevention. Maintain well-drained soil and take care to control root knot nematodes (which can exacerbate thew bacterial infection). Avoid damaging or wounding tomato plants during planting. You should also always remove all plant debris from the garden.

Once soils are infected with bacterial wilt, it isn’t technically curable. Your best bet is planting tomatoes in other parts of the garden. You can also try remediating the soil with diverse soil inoculants of beneficial microorganisms that can outcompete the pathogens.

Small, circular, and/or sunken lesions on fruit begin about one-half inch in diameter and later turn brown. You can often see a small black speck in the center of the lesion, which is why this disease is also called “tomato black dot” rot. Similar symptoms can appear on lower leaves and roots, leading to widespread rotting.

This fungus primarily takes hold on wet leaves and fruit, so avoid overhead irrigation at all costs. Rotate nightshade family crops around the garden and ensure well-drained soil.

Standard organic or conventional fungicides can control anthracnose, however, many gardener’s opt to remove infected fruit and wait for the next round of tomatoes.

Septoria leaf spots are circular and less than ¼ inch in diameter. They are speckled around the leaf and begin on the oldest growth first. The disease may start to cause yellowing, browning, and death of leaves. The spots won’t usually show up on fruit.

Improving air circulation is key for this disease. Avoid overhead irrigation, control weeds, and mulch around the base of the plants to prevent rainfall splash.

Remove and dispose of all diseased leaves. In a severe infection, you can apply fungicides such as copper or neem to stop the spread.

Rapid yellowing and wilting appear first. Then comes a white fungal appearance at the soil line near the base of the plant, as well as lesions that appear wet or soaked on the stems. Fruit also can take on a rotten, watery appearance.

The number one most important preventative method is removing dead leaves and plant debris. This fungus lives in the top few inches of soil, persisting on decomposing tomato matter. You should also purchase only disease-free plants, remove infected plant parts, avoid overhead irrigation, and sanitize garden tools. Widen spacing if it is a recurring problem.

Solarization of soil with clear plastic has proven successful for many growers. You can also use organic or conventional fungicides.

You will notice stems that start to look bleached and dried out, like a dead tree. The black scleorita (hard fungal structures) hang out in the soil near the base of the plant.

Continuous wetness and high humidity seem cause the highest infection rates. Keep the soil near the base of the plant as dry as possible using subsurface drip irrigation and a fluffy, lightweight mulch like straw. Avoid overhead irrigation and maintain proper aeration between plants.

In severe infections, copper and sulfur fungicides can be used.

Tomato roots first get distinctive brown lesions when infected with this fungus. They turn brown or yellowish and may begin to girdle or rot away. The above ground symptoms include wilting or death of plants in hot weather. If fruits come in contact with the pathogen, they get brown and tan concentric rings on the surface (hence the name “buckeye”).

Double-dig tomato beds with a broadfork and thoroughly amend with organic matter to improve drainage and soil structure. Avoid compacted soils and flooding at all costs. Try to maintain consistent soil moisture rather than fluctuating between dry and wet periods. Gardeners have seen some success mitigating the infection when the rotate with cover crops.

In soils with very poor drainage, you may opt for fungicide use.

Wilted and stunted growth are the initial signs of infection. Leaves may begin to turn yellow and brown, then get the characteristic curled appearance. Sometimes there are “bird’s eye spots” on fruit that look like raised circles with a white margin.

Researchers at the University of California Davis have found that soaking tomato seeds in hot water (above 130°F) for 25 minutes before planting can eliminate the pathogen. You should also thoroughly sanitize greenhouse structures and garden tools. Rotate nightshades around the garden every year.

Copper can be used to help control the infection, but it won’t completely eliminate bacterial canker. Always remove and destroy affected crop debris.