Tomatoes are one of the most popular vegetables to grow in home gardens. However, tomato plants are susceptible to various diseases that can severely impact your harvest. Knowing how to identify and treat common tomato diseases is crucial for any gardener who wants to enjoy a bountiful crop of juicy, flavorful tomatoes. This comprehensive guide covers the 15 most widespread tomato plant diseases and provides effective solutions to combat them.

Early Blight

Early blight is one of the most common and destructive tomato diseases. It is caused by the fungus Alternaria solani and favored by warm, humid conditions.

Symptoms

Small brown spots with concentric rings on leaves that gradually expand into large necrotic lesions.
Spots may also develop on stems and fruit.
Severely infected leaves turn yellow and drop.
Fruit lesions are dark, sunken and leathery.

Solutions

Provide good air circulation and avoid overhead watering.
Mulch plants to reduce soil splash onto foliage.
Remove and destroy affected leaves and fruit.
Apply fungicidal sprays containing chlorothalonil, myclobutanil or copper early in the season.
Rotate crops and avoid planting tomatoes in the same spot for consecutive years.
Plant resistant tomato varieties.

Late Blight

Late blight is a dangerous disease that spreads rapidly in humid, cool conditions. It is caused by the oomycete Phytophthora infestans, which was responsible for the Irish potato famine.

Symptoms

Irregular, water-soaked, greenish-black lesions on leaves that quickly expand, becoming brown and brittle.
Whitish fungal growth may appear on the underside of lesions in humid weather.
Stem lesions are dark brown to black and occur at stem nodes.
Fruit lesions are brown to greenish-black, firm and leathery with defined borders.

Solutions

Remove and destroy all infected plant material promptly.
Provide good air circulation and avoid overhead irrigation.
Apply fungicides containing chlorothalonil, mancozeb or copper weekly as a preventative.
Once infection occurs, switch to systemic products with active ingredients like azoxystrobin, cyazofamid or mandipropamid.

Septoria Leaf Spot

Septoria leaf spot is caused by the fungus Septoria lycopersici. It is favored by wet conditions and typically appears after the first fruit sets.

Symptoms

Small water-soaked circular spots on older leaves that develop gray centers with black dots (pycnidia).
As spots enlarge, they form a yellow halo. Leaves eventually turn yellow and drop.
Stem lesions are also possible.

Solutions

Remove lower leaves showing symptoms.
Apply chlorothalonil, mancozeb or copper sprays at 7 to 10 day intervals once disease is present.
Space and stake plants to promote air flow.
Rotate crops yearly and remove tomato debris after harvest.

Bacterial Spot

Bacterial spot results from infection by Xanthomonas campestris pv. vesicatoria. The bacteria enter plants through natural openings and wounds.

Symptoms

Small, water-soaked, greasy spots on leaves and stems that become brownish and papery with yellowing halos.
Black, scabby lesions on fruit.
Severe infection defoliates plants.

Solutions

Purchase certified, disease-free transplants.
Do not work in the garden during wet conditions.
Remove infected plant parts promptly.
Apply copper-based bactericides weekly as a preventative.
At the end of season, collect and destroy all plant debris.

Bacterial Speck

Bacterial speck is caused by Pseudomonas syringae pv. tomato.Infection occurs through natural openings and wounds during cool, moist conditions.

Symptoms

Tiny black spots with yellow halos on leaves and stems.
Fruit spots are small black dots that do not penetrate deeper than the skin.
Severe infection leads to leaf and fruit drop.

Solutions

Purchase certified disease-free transplants.
Avoid overhead irrigation to limit spread.
Apply copper-based bactericides as a preventative measure.
Do not work among wet plants.
Monitor for symptoms and remove affected plant parts promptly.

Bacterial Canker

Bacterial canker arises from Clavibacter michiganensis. Infection happens through natural openings in cooler weather.

Symptoms

Margins of leaves curl upward and turn brown.
Cankers form on stems as raised, brownish lesions that may crack open.
Fruit spots are corky and brownish, often appearing as rings.
Severe infection leads to wilting and plant death.

Solutions

Start with certified, disease-free transplants.
Remove infected plants or prune out cankers on stems.
Disinfect tools between plants with a 10% bleach solution.
Rotate crops yearly.
Apply copper sprays weekly when disease is present.

Target Spot

Target spot is caused by the fungus Corynespora cassiicola. It thrives in hot, humid weather and often appears mid to late season.

Symptoms

Circular, brown lesions with concentric rings on leaves, stems, and fruit. Lesions resemble a target.
Stems lesions are sunken with darker margins.
Fruit spots have light centers with dark borders.

Solutions

Provide good air flow and avoid overhead irrigation.
Remove infected leaves and stems.
Apply fungicides like mancozeb, chlorothalonil or azoxystrobin at 7-10 day intervals.

Buckeye Rot

Buckeye rot stems from the fungus Phytophthora parasitica. It requires prolonged warm, wet conditions to develop.

Symptoms

Circular, brown to black spots on ripening fruit that enlarge into sunken lesions. Lesions have distinctive concentric rings.
White fungal growth may appear on lesions in wet weather.
Infected fruit turn brown, shrivel and mummify on vines.

Solutions

Avoid overhead irrigation and allow soil to dry between waterings.
Stake plants to keep fruit off wet ground.
Remove and destroy any affected fruit promptly.
Apply fungicide sprays containing chlorothalonil, mancozeb or copper weekly.

Verticillium Wilt

Verticillium wilt is caused by the soil-borne fungus Verticillium dahliae. It enters plants through the roots and restricts water flow in the vascular system.

Symptoms

Yellowing and wilting of lower leaves progressing up the plant.
Brown discoloration of stem near the soil line.
Overall stunted growth.
Eventually the entire plant wilts and dies.

Solutions

Rotate crops. Do not plant tomatoes in the same spot for 3-4 years.
Plant resistant varieties like Celebrity, Mountain Spring or Defiant.
Solarize soil prior to planting to reduce fungal populations.
Remove and destroy affected plants promptly.

Fusarium Wilt

Fusarium wilt is another soil-borne disease resulting from Fusarium oxysporum f. sp. lycopersici. It enters through the roots and impairs water transport.

Symptoms

Yellowing and wilting of leaves on one side of plant or on individual branches.
Brown streaks visible within wilted stems when cut.
Plants are stunted and may eventually die.

Solutions

Use resistant varieties like Better Boy, Celebrity, Amish Paste or Ace 55.
Rotate crops. Avoid planting tomatoes in same spot for 3-4 years.
Solarize soil or apply biofungicides with Trichoderma to reduce fungal populations before planting.
Remove and destroy affected plants promptly.

Southern Blight

Southern blight arises from the fungus Sclerotium rolfsii and thrives in warm, humid climates. It attacks tomatoes close to harvest.

Symptoms

Yellowing of leaves starting from the base of the plant.
White fungal mycelium appears near soil line that can girdle and kill the stem.
Small tan fungal structures called sclerotia form on infected tissue.

Solutions

Improve drainage and avoid overhead irrigation.
Use stakes or cages to prevent contact between stems and soil.
Mulch well around plants.
Apply fungicides containing azoxystrobin to soil drenches.
Remove and destroy infected plants.

Powdery Mildew

Powdery mildew is caused by Oidium neolycopersici. It spreads rapidly in greenhouses and high tunnels with poor air circulation.

Symptoms

White talcum-like fungal growth on the upper surfaces of leaves and stems.
Infected leaves eventually turn yellow and die.
Reduced fruit quantity and quality.

Solutions

Improve air flow and reduce humidity in covered structures.
Avoid overhead irrigation late in the day.
Apply fungicides with myclobutanil, sulfur or neem oil every 7-10 days once disease appears.
Remove heavily infected leaves.

Gray Mold (Botrytis Blight)

Gray mold arises from the fungus Botrytis cinerea. It requires cool, humid conditions to spread.

Symptoms

Soft, brownish spots on leaves, stems and fruit that expand rapidly into a fuzzy gray fungal growth.
Infected fruit eventually rots.
Defoliation and plant death can occur in wet conditions.

Solutions

Improve air circulation between plants and avoid dense planting.
Remove affected leaves, stems and fruit.
Apply fungicides containing chlorothalonil, myclobutanil or fenhexamid preventatively every 7-10 days when cool, wet weather is expected.

Anthracnose

Anthracnose is caused by the fungus Colletotrichum coccodes. It spreads rapidly in warm, wet weather.

Symptoms

Small, sunken, water-soaked lesions on ripening tomatoes that enlarge to 1⁄2 inch with dark borders and lighter gray centers.
Raised black fungal structures may be visible in centers of lesions.
Fruit rot progresses rapidly.
Stem lesions are long and sunken with orange coloration.

Solutions

Use stakes or trellises to avoid soil contact with fruit.
Promptly remove infected fruit and prune out stem lesions.
Apply fungicide sprays containing chlorothalonil, azoxystrobin or mancozeb on a 7-10 day schedule when disease is present.

Tomato Mosaic Virus

Tomato mosaic virus (ToMV) causes mottling, discoloration and distortion of leaves and fruit. It is spread by contact between plants, workers and tobacco products.

Symptoms

Yellow mottling, curling and distortion of younger leaves.
Fruit show uneven ripening, mottling, bumps and distortions.
Infected transplants may appear stunted with dark green foliage.
No treatment once plants are infected.

Solutions

Start with certified virus-free transplants.
Do not use tobacco products when handling plants.
Control weeds that can harbor the virus.
Remove and destroy infected plants promptly.

Tomato Spotted Wilt Virus

Tomato spotted wilt virus (TSWV) causes ringspots, distorted growth and plant death. It is spread by various thrips species.

Symptoms

Leaf bronzing, yellowing and necrosis starting from leaf tips and margins.
Ring spots on fruit range from circles to irregular blotches.
Severe infection stunts plants and prevents fruit set.

Solutions

Use virus-free transplants.
Control thrips populations with insecticides and reflective mulches early in season.
Apply systemic insecticides like imidacloprid to transplants before setting out.
Remove and destroy infected plants promptly.

Conclusion

Tomatoes can fall victim to a range of fungal, bacterial and viral diseases. Successful prevention relies on proper cultural practices like rotating crops, staking plants, and improving air circulation. When conditions favor disease development, taking prompt action to remove infected plants and applying protective fungicide and bactericide sprays is key to safeguarding healthy plants. Selecting disease-resistant varieties can also help thwart many common tomato afflictions. With vigilance and quick response to emerging problems, gardeners can still reap bountiful harvests of delicious, wholesome tomatoes.

Save Your Tomato Plants From These 15 Common Diseases

Early Blight

Early blight is one of the most common and destructive tomato diseases. It is caused by the fungus Alternaria solani and favored by warm, humid conditions.

Symptoms

Small brown spots with concentric rings on leaves that gradually expand into large necrotic lesions.
Spots may also develop on stems and fruit.
Severely infected leaves turn yellow and drop.
Fruit lesions are dark, sunken and leathery.

Solutions

Provide good air circulation and avoid overhead watering.
Mulch plants to reduce soil splash onto foliage.
Remove and destroy affected leaves and fruit.
Apply fungicidal sprays containing chlorothalonil, myclobutanil or copper early in the season.
Rotate crops and avoid planting tomatoes in the same spot for consecutive years.
Plant resistant tomato varieties.

Late Blight

Late blight is a dangerous disease that spreads rapidly in humid, cool conditions. It is caused by the oomycete Phytophthora infestans, which was responsible for the Irish potato famine.

Symptoms

Irregular, water-soaked, greenish-black lesions on leaves that quickly expand, becoming brown and brittle.
Whitish fungal growth may appear on the underside of lesions in humid weather.
Stem lesions are dark brown to black and occur at stem nodes.
Fruit lesions are brown to greenish-black, firm and leathery with defined borders.

Solutions

Remove and destroy all infected plant material promptly.
Provide good air circulation and avoid overhead irrigation.
Apply fungicides containing chlorothalonil, mancozeb or copper weekly as a preventative.
Once infection occurs, switch to systemic products with active ingredients like azoxystrobin, cyazofamid or mandipropamid.

Septoria Leaf Spot

Septoria leaf spot is caused by the fungus Septoria lycopersici. It is favored by wet conditions and typically appears after the first fruit sets.

Symptoms

Small water-soaked circular spots on older leaves that develop gray centers with black dots (pycnidia).
As spots enlarge, they form a yellow halo. Leaves eventually turn yellow and drop.
Stem lesions are also possible.

Solutions

Remove lower leaves showing symptoms.
Apply chlorothalonil, mancozeb or copper sprays at 7 to 10 day intervals once disease is present.
Space and stake plants to promote air flow.
Rotate crops yearly and remove tomato debris after harvest.

Bacterial Spot

Bacterial spot results from infection by Xanthomonas campestris pv. vesicatoria. The bacteria enter plants through natural openings and wounds.

Symptoms

Small, water-soaked, greasy spots on leaves and stems that become brownish and papery with yellowing halos.
Black, scabby lesions on fruit.
Severe infection defoliates plants.

Solutions

Purchase certified, disease-free transplants.
Do not work in the garden during wet conditions.
Remove infected plant parts promptly.
Apply copper-based bactericides weekly as a preventative.
At the end of season, collect and destroy all plant debris.

Bacterial Speck

Bacterial speck is caused by Pseudomonas syringae pv. tomato.Infection occurs through natural openings and wounds during cool, moist conditions.

Symptoms

Tiny black spots with yellow halos on leaves and stems.
Fruit spots are small black dots that do not penetrate deeper than the skin.
Severe infection leads to leaf and fruit drop.

Solutions

Purchase certified disease-free transplants.
Avoid overhead irrigation to limit spread.
Apply copper-based bactericides as a preventative measure.
Do not work among wet plants.
Monitor for symptoms and remove affected plant parts promptly.

Bacterial Canker

Bacterial canker arises from Clavibacter michiganensis. Infection happens through natural openings in cooler weather.

Symptoms

Margins of leaves curl upward and turn brown.
Cankers form on stems as raised, brownish lesions that may crack open.
Fruit spots are corky and brownish, often appearing as rings.
Severe infection leads to wilting and plant death.

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