Tomatoes are one of the most popular vegetables grown in home gardens. However, they are susceptible to several fungal diseases that can severely impact tomato plant health and fruit production. The three most common tomato fungal diseases are early blight, late blight, and fusarium wilt. Learning how to properly diagnose and treat these diseases is crucial for growing healthy, productive tomato plants.

Understanding Tomato Fungal Diseases

Fungal pathogens affect tomatoes by colonizing either the leaves, stems, roots or fruits of the plant. The fungi can quickly spread to infect the entire plant, reducing vigor and yield. Tomato fungal diseases thrive in warm, humid environments. Once a tomato plant is infected, it is very difficult to eliminate the pathogen completely. Therefore, prevention and early treatment of infections are vital.

The development of fungal diseases depends on several factors:

Environmental conditions – Extended periods of warm, rainy, and humid weather promote fungal growth and disease development. Poor air circulation also enables fungal spore dispersal.
Susceptible varieties – Some tomato varieties are more prone to fungal diseases than others. Heirloom types tend to be more susceptible.
Unhealthy plants – Plants that are stressed due to improper care or poor soil conditions are more vulnerable to fungal pathogens. Proper fertilization, mulching, and irrigation helps strengthen plant defenses.
Inadequate garden sanitation – Fungal spores can overwinter in plant debris and soil. Removing affected plants and fallen leaves helps limit reinfection sources.

Recognizing Early Blight

Early blight, caused by the fungus Alternaria solani, is one of the most common tomato diseases. Symptoms typically appear on older foliage near the base of the plant. However, early blight can also affect stems, fruits, and younger growth in severe cases.

Early Blight Leaf Symptoms

Small brown spots on leaves which enlarge into circular lesions with concentric rings that resemble bullseyes. Lesions may be up to half inch in diameter.
Older lesions are darker in color and more irregularly shaped. They may connect and cover large sections of a leaf.
Severely infected leaves turn completely brown and brittle before withering and falling off. Defoliation typically progresses from older leaves upward.
Dark colored lesions may also appear on stems. Cankers can girdle stems, causing wilting above the damaged area.

Early Blight Fruit Symptoms

Sunken, dark colored lesions form on ripe fruit. Lesions are leathery in texture and may be up to an inch across.
Infected fruits often drop prematurely or ripen unevenly. The fungi can spread from diseased leaves into fruits through the stems.
Lesions on green fruit are typically small, brown, and slightly indented. Enlarging fruit may crack along the margins of lesions.

Diagnosing Late Blight

Late blight is caused by the oomycete Phytophthora infestans. It spreads rapidly under cool, wet conditions, quickly defoliating plants. Late blight also infects potato and related crops. There are now strains resistant to some fungicides, so accurate diagnosis is essential for effective management.

Late Blight Leaf Symptoms

Irregularly shaped olive green to brown lesions first appear on older leaves at margins or tips. Spots have indistinct edges and a water-soaked appearance.
Lesions rapidly coalesce, destroying large sections of leaf tissue which then turn brown and brittle. leaves wither quickly but often remain attached to stems.
Fuzzy white fungal growth may be visible on the underside of affected leaves in humid conditions. Rusty orange spores also form on leaf undersides.
Stems display grey-green or dark brown lesions that can girdle and kill stems above the infected area.

Late Blight Fruit Symptoms

Fruit symptoms begin as pale green, water-soaked patches, often at the stem end. Patches enlarge and darken rapidly into brown, greasy lesions.
Firm, white fungal growth develops on infected fruit during humid weather. Lesions may be surrounded by a light green halo.
Infected green fruit shrivel, turn brown or black, and drop from plants. Ripe tomatoes develop a tough, leathery texture.

Identifying Fusarium Wilt

The soil-borne fungus Fusarium oxysporum f. sp. lycopersici causes fusarium wilt disease. Once introduced, the fungus can persist in soil for years, making crop rotation essential for disease management. Resistant cultivars should be selected for susceptible sites.

Fusarium Wilt Leaf Symptoms

Initial symptoms appear first on oldest leaves. Leaves wilt during the daytime and recover overnight, but eventually do not revive.
Affected leaves turn yellow between the veins while the veins remain green, giving a mottled appearance. Leaves eventually turn brown and die.
Leaf symptoms typically appear on one side of the plant or on one branch initially. Eventually the entire plant wilts and dies.

Fusarium Wilt Stem Symptoms

Cutting stems lengthwise reveals dark brown streaks or discoloration within the vascular tissue. This diagnostic symptom differentiates fusarium wilt from other wilting disorders.
Lower stem tissue may feel spongy or rotten in advanced stages of disease. Severely infected plants are stunted and wilted.
Yellowing and death of older leaves precedes wilting of the entire plant. However, in some cases, plants collapse and die very rapidly.

Treating Early Blight Infections

While there are no chemical controls that can eliminate early blight once plants are infected, the following practices help slow disease development and reduce impacts:

Remove and destroy severely affected leaves which are the main source of spore production. Avoid composting diseased debris.
Improve air circulation around plants through proper spacing, staking, and selective pruning to reduce foliage wetness.
Apply protective fungicides containing chlorothalonil, mancozeb, or copper compounds before symptoms appear and repeat according to label instructions. Organic options include sulfur and bacillus subtilis.
Spread a layer of disease-free mulch under plants to prevent soil from splashing spores onto lower foliage. Use drip irrigation instead of overhead watering.
Rotate tomato crops onto different beds each year to avoid soil-borne inoculum buildup. Delay fall tilling to allow debris time to decompose.

Managing Late Blight Outbreaks

Once late blight is detected, aggressive measures are needed to contain it:

Inspect plants frequently and remove any affected leaves, stems or fruits immediately. It’s critical to prevent the establishment of sporulation sources.
Apply fungicide sprays containing chlorothalonil, mancozeb, copper compounds, or other labeled products every 5-7 days after initial symptoms appear or during cool, wet weather.
Keep tomato foliage as dry as possible by avoiding overhead irrigation and excessive densities. Stake, trellis or prune plants to enhance air movement. Remove nearby weeds.
Disinfect tools after working with infected plants to avoid spreading spores. Wash hands before handling uninfected plants.
At the end of the season, dispose of all tomato debris by burning, burying or hot composting. Do not add diseased residues to normal compost piles.

Controlling Fusarium Wilt

Since fusarium wilt fungus persists indefinitely in soils, management requires long-term practices:

Select wilt-resistant cultivars suitable for your region. Many hybrids have resistance bred into them. Grafting susceptible varieties onto resistant rootstocks is also effective.
Test soil pH and maintain around 6.5. Fusarium thrives in acidic conditions. Liming soil above pH 7 helps suppress the pathogen.
Improve drainage in affected areas and avoid compacting soil. Fusarium develops most readily in saturated or poorly aerated soil.
Solarize soil by covering it with clear plastic for 6-8 weeks during hot weather to reduce fungal populations.
Remove and destroy infected plants immediately. Do not compost wilt-diseased residues.
Avoid planting tomatoes, potatoes, peppers or eggplants in the same location for at least 3 years.

Frequently Asked Questions About Tomato Fungal Diseases

1. How do I know if my tomato plant has a fungal disease?

Look for key symptoms like leaf spots, wilting, stem cankers, and fruit rot. Compare to descriptions and images to identify the specific disease. Lab testing can also confirm the fungal pathogen.

2. What causes fungal diseases in my tomato plants?

Various fungal organisms such as Alternaria, Phytophthora and Fusarium species. They infect plants through spores when conditions are favorable. Preventing introduction is key.

3. Are tomato fungal diseases treatable?

Early blight and late blight may be suppressed but not cured using fungicides. However, fusarium wilt cannot be reversed. Resistance and prevention are most important for managing wilt.

4. How do I prevent fungal diseases from infecting my tomatoes?

Use resistant varieties, test soil, maintain proper plant spacing and avoid wet foliage. Rotate plant locations yearly. Remove and destroy diseased debris promptly.

5. Should I use fungicide sprays to prevent tomato fungal diseases?

Preventative fungicide applications can be made based on disease risk. But they must be repeated regularly to be effective. Cultivar selection and cultural practices are preferable.

6. If my tomatoes had late blight, can I compost the plant waste?

No, late blight pathogens can survive in compost piles. Burn, bury or hot compost affected plant residues. Sterilize tools and stakes before reuse.

7. How long do I need to rotate tomatoes after fusarium wilt problems?

Avoid planting tomatoes or related crops in affected areas for at least 3 years, preferably longer. Solarization helps reduce fungal populations.

8. What are the best tomatoes to grow to avoid fungal diseases?

Choose resistant hybrids or disease-tolerant heirlooms suitable for your climate. Consult regional vegetable gardening guides for recommendations.

9. Should I prune my tomato plants to improve air circulation?

Selective pruning to reduce dense foliage, especially lower leaves, can aid airflow and foliage drying. But avoid excessive pruning which stresses plants.

10. Is early blight on tomatoes detrimental to eating the fruits?

Early blight lesions on tomato fruit are superficial and do not affect eating quality. However, late blight renders fruits inedible.

Conclusion

Tomato fungal diseases like early blight, late blight, and fusarium wilt can be devastating but are manageable with accurate identification and integrated disease management. Examine plants frequently for symptoms, remove affected parts promptly, follow recommended fungicide programs, utilize resistant cultivars, and employ preventive cultural techniques. With proper diagnosis and treatment, healthy and productive tomato crops are achievable even when fungal pathogens are present. Consistent vigilance, sanitation and smart practices will limit losses and help sustain tomato yields season after season.

Diagnosing and Treating Three Common Tomato Fungal Diseases