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Tomatoes are one of the easiest garden crops to grow, producing an abundance of deliciously sweet fruits all summer long. But did you know that there are a bunch of tomato plant diseases just waiting to wreak havoc on your crop? Many of these diseases take advantage of weak plants in less-than-ideal growing conditions, spreading quickly and ruining your horticultural efforts.
To maximize your chances of an abundant tomato crop in your home garden, we’ve found out everything you need to know about the most common tomato diseases, including how to prevent infection and what action to take on the affected area if they do occur.
1. Anthracnose (Colletotrichum spp.)
Anthracnose is a fungal disease that spreads quickly in moist conditions. It causes dark lesions on all parts of the tomato plant and can lead to widespread fruit rot. To prevent it from affecting your tomato plants, keep tomato plants well-ventilated, avoid overhead watering, and harvest tomatoes as soon as they are ripe.
Treatment: There are no effective treatments for anthracnose – affected plants should be removed and destroyed.
2. Bacterial Canker (Clavibacter michiganensis subsp. michiganensis)
Bacterial canker spreads rapidly, causing all parts of the tomato plant to wilt and turn yellow. Plant stems split, and the fruits develop ugly brown lesions. Bacterial canker is spread via contaminated tools, so it is important to sanitize equipment regularly. Copper-based bactericides can be used in high-risk areas.
There is no effective treatment for diseased plants. Affected plants should be removed and destroyed.
3. Bacterial Spot (Xanthomonas campestris pv. vesicatoria)
Bacterial spot disease appears as small, wet-looking lesions on all parts of the tomato plant. This bacterial speck disease spreads rapidly in warm, humid conditions.
To prevent this disease from impacting your plant, keep humidity low (avoid high humidity) by increasing ventilation and avoiding overhead watering. Copper-based preventative treatments can be useful in high-risk areas.
4. Blossom End Rot
Blossom end rot is caused by calcium deficiency or irregular watering, resulting in dark, soft fruits at the blossom end. To prevent this disease, it’s important to water regularly to maintain consistent soil moisture and sprinkle crushed eggshells around the base of plants.
If blossom end rot is present, apply a calcium-based fertilizer and increase watering frequency. Remove and compost any affected fruits.
5. Early and Late Blight (Alternaria solani, Phytophthora infestans)
Blight is a devastating tomato disease that many growers have encountered. Both early blight and late blight cause yellow-brown lesions on leaves and stems, leading to plant collapse and fruit rot.
The best way to prevent this from happening to your tomato plants is to ensure they are well-spaced and prune lower leaves to increase good air circulation. Avoid watering from above and keep growing areas well-ventilated. Late blight can be quite damaging during seasons of wet weather, including heavy rain.
Treatment: It can be hard to save tomato plants affected by blight, but removing affected older leaves early in the disease can sometimes be effective. In severe cases, the entire plant should be removed and destroyed.
6. Fusarium Wilt (Fusarium oxysporum f. sp. lycopersici)
Fusarium wilt is a soilborne fungus disease that causes the lower leaves of tomato plants to wilt and turn yellow. As the disease progresses, symptoms often seen in the plant include loss of developing tomato fruits and stunting of new growth.
Crop rotation can help prevent a buildup of fungal spores in the soil. Placing clear plastic over the soil in full sun for a month will kill existing fungal spores.
7. Gray Mold (Botrytis cinerea)
Gray mold causes grayish-brown fuzzy growth on the leaves, stems, and fruit of tomato plants. Gray mold spreads through airborne spores and thrives in cool, humid conditions. If you notice this tomato disease, remove and destroy affected leaves and treat the remaining foliage with an organic fungicide containing copper or sulfur.
8. Mosaic Viruses
Three mosaic viruses affect tomato plants: tomato mosaic virus,
It’s best to use companion plants during the growing season to attract beneficial insects that control aphid populations.
9. Powdery Mildew (Leveillula taurica)
Powdery mildew causes a white, powdery growth on all parts of the tomato plant. The leaves will become distorted, and the fruit will drop prematurely. This fungal disease spreads quickly via airborne spores. If you notice this disease, remove and destroy infected leaves, then apply a sulfur-based fungicide.
10. Root-Knot Nematodes (Meloidogyne spp.)
Root-knot nematodes are microscopic worms that infect the roots of tomato plants. The roots become deformed and struggle to provide the plant with sufficient water and nutrients, resulting in stunted growth and wilting.
The best preventative measure is to avoid growing tomatoes in the same area year after year – crop rotation prevents a build-up of nematodes in the soil.
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11. Septoria Leaf Spot (Septoria lycopersici)
Septoria leaf spot is a fungal disease that causes small circular lesions with dark borders on the lower leaves of tomato plants. The plant quickly becomes weakened, and crop yields are poor. To prevent this disease, it’s best to water early in the day and avoid splashing the leaves. To conserve moisture, mulch around the base of the plants. Treat the plant with a copper-based fungicide.
12. Southern Blight (Sclerotium rolfsii)
Southern blight causes tomato plant stems to turn yellow and rot near the ground, resulting in the complete loss of the plant. It is spread through infected plants, soil, and plant debris. The best way to prevent this is to keep the soil around tomato plants clear of plant matter.
13. Tomato Spotted Wilt Virus (TSWV)
Tomato spotted wilt virus is spread by thrips and causes characteristic rings on developing fruit. You may also see dark spots on the leaves and stunted growth.
As there is no cure for this virus, affected plants must be removed and destroyed. Control thrips by attracting beneficial predators such as lacewings, parasitoid wasps, and ladybugs.
14. Tomato Yellow Leaf Curl Virus (TYLCV)
Tomato yellow leaf curl virus is spread by whiteflies and causes upward curling and yellowing of tomato plant leaves. While there is no effective treatment for leaf roll, it’s simply best to remove and destroy any affected plants and Control whitefly populations with insecticidal soap or neem oil.
15. Verticillium Wilt (Verticillium spp.)
Verticillium wilt is a soilborne fungal disease that causes wilting and yellowing, often only on one side of the plant. If verticillium wilt is prevalent in your area, grow resistant varieties (marked with a ‘V’ on the label).
In addition, this soilborne pathogen can only be eradicated by soil fumigation. All affected plants should be removed and destroyed.
16. White Mold (Sclerotinia sclerotiorum)
White mold causes a cotton-like fungal growth on tomato plants’ stems, leaves, and fruit. To prevent white mold, maintain a good crop rotation schedule, keep plants well-ventilated, and avoid overhead watering. Organic treatments, such as Coniothyrium minitans, can eliminate soilborne spores.
