Tomato Diseases: Identification and Solutions
By: Jessie Keith
Tomatoes are the roses of vegetables–everything attacks them. So, gardeners can count on experiencing any number of tomato diseases in their growing experience. It pays to grow disease-resistant tomatoes, but lots of the best heirlooms don’t fall into this category. That’s why tomato growers need to be armed with knowledge and IPM (integrated pest management) tools to keep harvests high. Learning how to spot the most common tomato diseases is a start.
Plant diseases are typically either fungal, bacterial, or viral. Some cause quick plant death, but others can be managed–allowing gardeners to eke out a harvest until the end of the season. But avoidance is the best starting point.
The four keys to avoiding tomato diseases are:
- Start with healthy plants.
- Choose a disease-resistant variety.
- Plant them in disease-free soil.
- Give them the best care.
Starting with healthy plants, a healthy environment, and keeping plants stress-free will help keep them disease-free, but pests or diseased weeds, or even wind can still bring disease into the garden. People can, too. Gardeners need to stay watchful.
If you have never experienced serious tomato diseases in your garden, you can feel confident planting heirlooms or family favorites with less resistance. But, always choose disease-resistant varieties if you have experienced diseases in the recent past. You might also consider growing tomatoes in containers to ensure that soil-borne diseases are not a problem. (Click here to learn how to grow tomatoes in containers.)
Top Disease-Resistant Tomatoes
Before reading the depressing litany of common tomato diseases, feel encouraged by the power of super disease-resistant tomatoes. Plant breeders constantly work hard to create new and wonderful tomato varieties able to beat diseases and produce high yields of delicious tomatoes. When identifying a disease-resistant tomato, refer to the Tomato Disease Resistance Code list below to better understand the code system. Here is an example of five good, tough tomatoes that resist multiple diseases.
‘Galahad’ (F3, GLS, LB, N, TSWV): The new, 2020 All-America Selections Winner ‘Galahad’ is a big, red, slicing tomato with excellent flavor that resists five diseases!
‘Granadero’ (F2, PM, TMV, V, N, TSWV): Sauce tomato lovers should try this super disease-resistant paste tomato with uniform, red, well-flavored fruits. It is also an AAS award winner.
‘Mountain Merit‘ (F3, LB, N, TSWV, V): Lots of large, red tomatoes with good, sweet flavor are produced on this compact bush tomato.
‘Toronjina’ (F2, LM, TMV): Highly disease-resistant plants produce lots of sweet and tart, orange cherry tomatoes on shorter indeterminate vines.
‘Sakura‘ (F2, LM, TMV, N): Red cherry tomatoes are produced early and in abundance on this long-vined, highly disease-resistant tomato.
Good cultural practices will also help tomatoes fight disease. Plant them in very well-drained, aerated, raised beds amended with Black Gold Garden Soil, and keep plants strong and vigorous by feeding them with a tomato & vegetable fertilizer. It also helps to encourage air-flow by spacing plants well (3 to 4 feet apart, or wide enough to walk around) and keeping them pruned (click here for a tomato pruning tutorial). Drip irrigation helps keep plants drier up top, which can reduce the spread of diseases. Remove and discard infected plants as you see them, and at the end of the season, clean all plant material from your vegetable garden for good measure. Then at planting time, mulch tomatoes with a layer of straw or Black Gold Garden Compost Blend to help keep disease-carrying weeds at bay. (Click here for more tips on how to grow robust tomato plants from seed to harvest.)
Tomato Disease Resistance Codes
When seeking out a disease-resistant tomato, you will see these codes indicating resistance. The most common diseases are covered in this piece. (Adapted from Johnny’s Seeds Growers’ Library)
HR = High Resistance IR = Intermediate Resistance
- A | Anthracnose | Fungus
- AS | Alternaria Stem Canker | Fungus | Alternaria alternata f. sp. lycopersici
- CRR | Corky Root Rot | Fungus | Pyrenochaeta lycopersici
- EB | Early Blight (Alternaria Blight) | Fungus | Alternaria solani
- F (2, 3)| Fusarium Wilt | Fungus F. oxyporum f. sp. lycopersici
- FOR | Fusarium Crown and Root Rot | Fungus | Fusarium oxysporum f. sp. radicis–lycopersici
- GLS | Gray Leaf Spot | Fungus | Stemphylium solani
- LB | Late Blight | Water Mold | Phytophthora infestans
- LM | Leaf Mold | Fungus | Cladosporium fulvum
- N | Roundworm | Nematode | Meloidogyne arenaria, M. incognita, M. javanica
- PM | Powdery Mildew | Fungus Oidium lycopersicum
- ToANV | Tomato Apex Necrosis Virus
- ToMV | Tomato Mosaic Virus | Tobamovirus
- TSWV | Tomato Spotted Wilt Virus | Tospovirus
- TYLCV | Tomato Yellow Leaf Curl Virus | Begomovirus
- V | Verticillium Wilt | Fungus | Verticillium albo–atrum
Tomato Foliage Diseases
These are the first tomato diseases that you will see and experience. All leaf spot diseases start from the bottom up–beginning with older leaves. Here are the top 5 most common types that you will see.
Bacterial Leaf Spot
The common leaf spot (Xanthomonas spp.) results in spots that are small, dry, brown, and often surrounded by yellow halos. It disease intensifies and spreads further with excess rain, overhead watering, and when plants are planted too close together. As it progresses, it can also cause spotting on fruits and cankers on stems.
You cannot get rid of bacterial leaf spot once you have it, but you can slow its damage. To reduce its proliferation, increase airflow by pruning off unnecessary and badly infected branches. Keep it from taking hold in the first place by spacing plants well to encourage airflow. Cleaning up your garden yearly is also essential. The disease is maintained from year to year on infected crops and weeds in the tomato family.
Early Blight and Late Blight
These two blights are the most common diseases of tomatoes.
Early Blight (Alternaria tomatophila and Alternaria solani): The leaf spots are pretty distinctive; circular lesions appear, reaching up to a half an inch in diameter with dark concentric circles inside. Early blight can occur at the seedling stage by causing seedling rot (damping-off). At later stages, it causes leaf blight on older leaves, stem cankers, and black fruit rot.
Late Blight (Phytophthora infestans): The deadly disease first causes large brown leaf spots on older leaves, followed by stem lesions, and discolored, oily patches on fruits. It’s the noxious disease that caused the Irish Potato Famine, which is a testament to its severity. It kills tomatoes more slowly, but it destroys fruits and will eventually kill whole plants. Tomatoes subjected to drought stress will die more quickly.
Both early and late blight diseases are controlled by avoidance, cleanliness, and rotation. The blights survive and overwinter on infected plant material or in the soil. To prevent tomato blight, plant only healthy plants that you have grown from seed or purchased from a reliable grower. Also, plant only blight-resistant varieties (check out this list from Cornell University). If you find diseased plants, immediately remove them from the garden, and keep them from the compost bin. Bag and toss them instead. Keep beds weeded to remove weedy tomato relatives that can get blight, like nightshade and ground cherry. Next, rotate crops on a three-year cycle to help keep soil disease-free where you experienced blight. That means planting your tomatoes in a new spot each year and allowing three years to pass before planting them in the same spot. The soil should be rid of the disease after this time.
Powdery mildew (Erysiphales fungi): The easy-to-identify powdery mildew is a common fungal infection that attacks leaves, causing white, powdery looking surfaces and blotches, particularly from mid to late summer. It is not deadly, but it will cause plants to decline more quickly and put a stop to good fruit production.
To stop powdery mildew, give plants plenty of sun, water, and airflow. Prune off diseased stems as you see them (clean your pruners well after cutting any diseased plant). Finally, apply the organic fungicide Green Cure, which quickly stops powdery mildew. Apply it, at first sight, to stop the disease in its tracks.
Tobacco Mosaic Virus
When tomatoes contract tobacco mosaic virus, they develop yellow mosaic patterns across the foliage and leaves often become elongated and almost ferny. Once you have it, or any other virus, the only thing that you can do is quickly remove and dispose of the plants and then rotate your crops. The best means of control is prevention. Grow resistant tomatoes, and make sure you buy seed or purchase plants that are certified to be disease-free.
These affect the whole plant causing overall wilt and decline. Both diseases exist in the soil. The best means of beating them is to plant resistant varieties. When susceptible plants become infected, it’s a death sentence. Plants must be removed from the garden.
Fusarium Wilt (F)
Fusarium wilt (Fusarium oxysporum sp. lycopersici) is the most common tomato wilt. At its first signs, older leaves wilt, turn yellow, then brown, and then fall. The stunted plants will eventually die. To beat it, look for resistant varieties, discard diseased plant material, and rotate on a three-year cycle.
Verticillium Wilt (V)
Verticillium wilt (Verticillium albo–atrum) is less common than fusarium wilt and is typically seen late in the season when soils are cooler. Its first symptoms are v-shaped blotches on the lower leaves, followed by browning veins and blotches. Symptoms then spread upwards, causing wilting and leaf damage. If you were to cut into the stem, the internal veins would be brown and discolored from the ground up to 12 inches. Treat it as you would fusarium wilt.
Tomato Fruit Diseases
Aside from the ugly oily patches caused by late blight (above) and the common black-based fruits caused by blossom end rot or irregular bases caused by cat-facing (see below), most other tomato fruit problems are fungal or bacterial.
Anthracnose Tomato Spot (A)
Anthracnose tomato spot is a fungal disease that appears as sunken bull’s-eye marks on ripe fruits. Several steps can be taken to reduce the disease on developing fruit. Refrain from overwatering, which will reduce moisture on the leaves and the spread of the disease. Remove and dispose of damaged fruit, and prune to increase airflow can keep fruits from developing this disease on the vine.
Various Fruit Rots
There is a whole suite of fungal and other fruit rots that can damage good, ripe fruit on the vine. You can always identify a fungal spot on fruit by its bull’s-eye appearance. The center of the eye is where the fungal spore took hold, and the radiating circles show its progressive cycle of infection. The treatment of these diseases is the same as for Anthracnose tomato spot. Good airflow is always key in keeping fungal diseases at bay.
Bacterial Spot and Bacterial Canker
Some bacterial spot diseases of leaves can impact fruits. Bacterial fruit spots are smaller than those caused by fungal diseases, brown or black towards the center, and often surrounded by rings of yellow or green. In the case of bacterial canker, the spots are ringed in white with a green or dark-brown center. Sometimes the spots are raised. When fruits have bacterial spots, this means that it is time to remove and dispose of the whole plant.
Disorders often look like diseases, but they are caused by either nutrient deficiencies or adverse weather conditions rather than disease-causing fungi, bacteria, or viruses. Even better, they can be cured.
Fruit blossom end rot (caused by calcium deficiency), splitting or cracking (caused by excessive water or temperature fluctuations), fruit toughness, cat-facing, and reduced productivity (caused by cool temperatures) are the most common disorders of tomato fruit. Leaves with nutrient deficiencies can show all manner of yellowing or poor pigmentation, but if you feed your tomatoes well with a tomato fertilizer all season, your plants shouldn’t suffer any nutrient deficiencies (unless you have soil with severely acid or basic soil pH). Problem solved. Generally, if you plant your tomatoes in warm conditions, feed and care for them well, you can avoid most tomato disorders.
Can’t find your tomato problem here? Then ask our garden experts on our Ask a Garden Expert page and upload a photo of your plant! We will help you identify the problem and gprovide solutions.
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