Tomatoes are one of the most popular crops grown in home vegetable gardens. However, they are susceptible to several diseases that can significantly reduce yields and fruit quality if left uncontrolled. Knowing how to identify and treat the most common tomato diseases is critical for any gardener wishing to successfully grow this crop. This article provides an in-depth overview of 8 major tomato diseases, including early blight, late blight, septoria leaf spot, bacterial spot, bacterial canker, fusarium wilt, verticillium wilt, and tomato mosaic virus. We’ll explore symptoms, causes, treatments, and prevention methods for each disease to help you develop an effective disease management strategy in your own tomato patch.
Early Blight
Early blight is one of the most common and destructive tomato diseases, attacking plants throughout the growing season. This fungal disease thrives under wet, humid conditions.
Symptoms
- Dark brown to black lesions on older leaves near the bottom of plants. Lesions have distinct concentric rings giving them a “bull’s eye” appearance.
- Leaves yellow, wither and drop off, exposing fruits to sunscalding.
- Small, dark spots form on stems and leaf stalks.
- Fruits can develop leathery, brown spots.
Causes
- Caused by the fungus Alternaria solani.
- Spreads via air-borne spores and infected seed.
- Favored by warm, wet, humid weather.
Treatment
- Improve air circulation around plants through proper spacing and pruning.
- Mulch plants to prevent soil from splashing up onto foliage.
- Apply chlorothalonil, mancozeb or copper-based fungicide sprays weekly starting when first fruits form.
- Remove and destroy severely infected plants and fallen leaves and fruits.
Prevention
- Choose resistant varieties like Defiant, Mountain Merit or Iron Lady.
- Rotate tomato planting areas each year.
- Prune plants to improve air circulation.
- Stake and trellis plants to keep foliage off the ground.
- Apply mulch around plants to prevent soil from splashing onto leaves.
- Water at the base of plants, avoiding wetting foliage.
Late Blight
Late blight is a dangerous tomato disease that spreads rapidly under cool, wet conditions. It is the same disease that caused the Irish potato famine. Entire tomato crop can be destroyed in just a few weeks by late blight.
Symptoms
- Water-soaked, grey-green spots on leaf margins and tips that quickly expand into large brown lesions.
- White fungal growth develops on the underside of affected leaves in wet weather.
- Stems, petioles and upper surfaces of leaves develop dark brown to black lesions.
- Brown to black lesion form on fruits.
Causes
- Caused by the fungus-like pathogen Phytophthora infestans.
- Spreads via microscopic spores carried by wind, rain, insects, and garden tools.
- Thrives under cool, wet conditions.
Treatment
- Remove and destroy all infected plants immediately.
- Apply copper-based fungicide sprays weekly as a protective barrier.
- Improve air circulation around plants through proper spacing and staking.
Prevention
- Monitor plants vigilantly and remove infected plants promptly.
- Plant resistant varieties like Mountain Merit, Iron Lady, or Legend.
- Avoid overhead watering. Water at the base of plants instead.
- Stake, prune and space plants appropriately to promote good air circulation.
- Remove solanaceous weeds like nightshade which can harbor the disease.
- Disinfect tools and equipment regularly with a 10% bleach solution.
Septoria Leaf Spot
Septoria leaf spot is a common fungal disease of tomato foliage. It appears as small circular spots on leaves and stems during cool, wet weather.
Symptoms
- Small (1/8 to 1/4 inch), circular spots with dark edges and tan centers on leaves.
- Spots may merge and turn leaves yellow.
- Tiny black dots (pycnidia) develop in the centers of spots.
- Stems develop elongated, dark lesions.
Causes
- Caused by the fungus Septoria lycopersici.
- Spreads via wind, rain splash, and contaminated seed.
- Thrives in cool, wet weather.
Treatment
- Improve air circulation around plants through proper spacing and staking.
- Mulch plants to prevent soil from splashing up onto foliage.
- Apply chlorothalonil or copper-based fungicide sprays.
Prevention
- Use disease-free seeds and transplants.
- Space plants appropriately to allow good air movement.
- Stake, trellis and prune plants to improve air circulation.
- Remove infected leaves promptly.
- Rotate tomato planting area each year.
- Avoid overhead watering.
Bacterial Spot
Bacterial spot is a common disease across warm, humid tomato growing regions. It is characterized by small lesions on leaves, stems and fruits. Severe infection can defoliate plants.
Symptoms
- Small, brown, watersoaked lesions on leaves which grow into large spots with yellow halos.
- Raised, brown, scabby lesions on fruits.
- Dark, cracked lesions on stems.
- Leaf spots and lesions often have concentric rings giving a “target-like” appearance.
- Heavily infected leaves turn yellow and drop off.
Causes
- Caused by four species of bacteria: Xanthomonas euvesicatoria, X. vesicatoria, X. perforans, and X. gardneri.
- Bacteria enter plants through natural openings and wounds.
- Spread by wind, rain splash, insect, contaminated seed and garden tools.
- Thrives in warm, wet weather.
Treatment
- Apply copper-based bactericide sprays.
- Improve airflow around plants through proper spacing and staking.
- Prune infected leaves and branches.
- Disinfect tools and equipment regularly.
Prevention
- Plant resistant varieties like Mountain Spring, Plum Regal, or Fletcher.
- Use disease-free transplants and seeds.
- Rotate plantings to different areas of the garden each year.
- Stake and trellis plants to promote good air circulation.
- Avoid overhead watering.
- Control insect and weed hosts.
Bacterial Canker
Bacterial canker causes shoot dieback and leaf spots. It can spread rapidly in warm, wet conditions through rain and contaminated equipment.
Symptoms
- Margins of leaves turn brown and wilt.
- Dark lesions appear on stems and branches.
- Stems and branches collapse, shrivel and die from the point of infection downwards.
- Small, dark spots develop on fruits.
Causes
- Caused by the bacterium Clavibacter michiganensis subsp. michiganensis.
- Enters plants through wound sites and natural openings.
- Spread by wind-driven rain, overhead irrigation, insects, contaminated seed and tools.
Treatment
- Prune infected branches several inches below visible symptoms.
- Disinfect tools with 10% bleach between plants.
- Apply copper-based bactericide sprays.
- Improve airflow by proper spacing and staking.
Prevention
- Use certified disease-free seed and transplants.
- Rotate tomato planting areas each year.
- Control insect and weed hosts.
- Sanitize tools, equipment and gloves regularly in 10% bleach solution.
- Stake and trellis plants to improve airflow.
- Water at the base, avoiding wetting foliage.
Fusarium Wilt
Fusarium wilt is a common soil-borne fungal disease that causes rapid wilting and death in tomato plants. It survives in the soil for many years.
Symptoms
- Leaves wilt and droop on one or more branches.
- Inner stem tissue appears brown or reddish-brown when cut.
- Wilting advances up the plant until the entire plant dies.
- Lower leaves yellow and drop.
- No fungal growth visible on the exterior of the plant.
Causes
- Caused by the soil-borne fungus Fusarium oxysporum f. sp. lycopersici.
- Enters plants through the roots.
- Survives in soil for years via durable spores.
Treatment
- No chemical controls available.
- Pull up and dispose infected plants promptly.
Prevention
- Plant resistant varieties like Celebrity, Better Boy, Ace 55 or Marglobe.
- Solarize soil or practice crop rotation with non-solanaceous plants to reduce fungal populations.
- Disinfect tools and equipment regularly.
Verticillium Wilt
Verticillium wilt causes wilting, yellowing, and plant death. It survives in the soil for many years, making crop rotation essential for prevention.
Symptoms
- Leaves wilt and turn yellow beginning on the lower parts of plants.
- Brown discoloration develops inside the stems near the soil line.
- Leaf edges may turn brown or black (early blight symptom).
- Entire plant wilts and dies.
- No fungal growth visible externally.
Causes
- Caused by the soil-borne fungus Verticillium dahliae.
- Enters plants through the roots.
- Persists in soil via durable resting structures called microsclerotia.
Treatment
- No fungicides available. Must pull up and dispose of infected plants promptly.
Prevention
- Plant resistant varieties like Mountain Fresh Plus, Mountain Merit and Iron Lady.
- Practice at least 2-3 year crop rotation.
- Solarize soil using clear plastic mulch to kill fungal resting structures.
- Control solanaceous weeds like nightshade.
Tomato Mosaic Virus
Tomato mosaic virus causes mottling, mosaic patterns, and distortion of leaves and fruits. It is transmitted by insects, human handling, and contaminated tools.
Symptoms
- Yellow mottling, mosaic patterns on leaves.
- Leaves distorted, curled, stunted.
- Plants stunted.
- Fruits show pale yellow blotches and uneven ripening.
Causes
- Caused by Tomato mosaic virus.
- Spread by aphids, human hands, tools, and infected seed.
Treatment
- Remove and destroy infected plants immediately.
- Control aphid populations.
- Disinfect tools and hands regularly.
Prevention
- Plant resistant varieties.
- Control weeds and insects like aphids.
- Use virus-free seed and transplants.
- Do not smoke near plants.
- Wash hands and disinfect tools between plants.
Conclusion
Tomatoes are prone to several destructive diseases that can wipe out crops quickly if left uncontrolled. However, by accurately identifying diseases early and promptly applying recommended management strategies, tomato plants can thrive and provide bountiful yields. Scout plants frequently, control weeds/insects, choose resistant varieties, employ preventative measures like crop rotation and sanitation, and be prepared to take action with appropriate fungicides or bactericides when needed. With vigilance and proper care, your tomato patch can flourish and provide an abundant harvest despite the array of potential diseases.
Frequently Asked Questions About Tomato Diseases
Here are some common questions and answers about identification, treatment, and prevention of major tomato diseases:
How can I tell if my tomatoes have early blight or septoria leaf spot?
Look closely at the leaf lesions. Early blight spots have concentric rings giving a bull’s eye pattern. Septoria spots are circular but lack the bull’s eye appearance, instead developing tiny black pycnidia in the center.
What causes spots on my tomato leaves?
Numerous diseases can cause leaf spots including early blight, septoria leaf spot, and bacterial spot. Compare symptoms to pictures to identify the disease. Prevent spread by improving airflow.
How do I treat fusarium or verticillium wilt in tomatoes?
There are no chemical treatments for these soil-borne fungal wilts. Remove and destroy affected plants immediately. Improve soil health through rotation and solarization to reduce the fungal populations for future years.
What causes the spots on my tomato fruits?
Bacterial spot, early blight, anthracnose, and other diseases can cause spots on tomato fruits. Check leaves and stems for corresponding symptoms to identify the disease. Prevent issues by improving airflow and not splashing soil onto plants.
Why do my tomato leaves have yellow splotches and curling?
These are common symptoms of tomato mosaic virus, transmitted by insects and contact. Remove and destroy affected plants immediately. Control insect vectors like aphids and tobacco hornworms.
How do I treat late blight in my tomatoes?
Late blight is difficult to control once started. At first signs, remove and destroy all infected plants and apply fungicide sprays. Avoid overhead watering and promote good airflow through proper spacing and staking.
What causes the brown wilting on my tomato plants?
Fusarium and verticillium wilts cause similar wilting symptoms. Check stem interiors for brown discoloration. Improve soil conditions to reduce fungal populations. Solarization and long rotations help.
How can I prevent tomato diseases naturally?
Choose resistant varieties, rotate planting areas, remove weeds/debris, use disease-free seed, apply mulch, improve airflow, avoid overhead watering, and promptly remove infected plants. Maintaining optimal growing conditions is key.
Conclusion
Identifying and managing common tomato diseases is essential for every gardener in order to protect yields and quality. Learn to recognize early symptoms of diseases and quickly take appropriate treatment and preventative steps. Sanitation, proper plant care, and control of disease vectors are critical. Remove and destroy infected plants promptly to avoid spread. With quick identification and action, your tomato crop can thrive and keep producing all season long despite the various disease threats.