How to Control Fungal Diseases in Tomatoes and Effective Management Strategies

Tomatoes (Solanum lycopersicum) are a popular crop, but they are susceptible to various fungal diseases that can cause significant damage to the plants and reduce yield. To ensure healthy tomato plants and a successful harvest, it is essential to implement effective management strategies for controlling fungal diseases.

These include using disease-resistant varieties, crop rotation, good sanitation practices, and judicious use of fungicides. This article will discuss common fungal diseases of tomato plants and provide practical tips on preventing and managing them.

How to Control Fungal Diseases in Tomatoes

Common Fungal Diseases of Tomato Plants

Fungal diseases are a common problem for tomato plants, caused by pathogens such as damping-off, early blight, septoria leaf spot, powdery mildew, verticillium wilt, late blight, and southern blight. Other pathogens include cercospora leaf mould, fusarium wilt, grey leaf spot, white mould, Alternaria stem canker, corky root rot, didymella stem rot, fusarium crown and root rot, fusarium foot rot, and buckeye rot.

Factors Contributing or Favorable Conditions for Fungal Diseases Spread

Favorable conditions for spreading fungal diseases in tomato plants include air temperature and humidity, soil moisture, pests that transmit the disease, nutritional disorders, and lack of sanitation.

Early Blight Disease and Effective Management Strategies

It is caused by a fungus that creates small black lesions, mostly on older foliage, which grows in size and develops a bull’s eye pattern with concentric rings. Yellowing of surrounding tissue may also occur.
High temperatures and humidity can kill much of the foliage. Lesions on stems are similar and can girdle the plant.
The fungus can also infect the fruit through the calyx or stem attachment, causing lesions that often involve nearly the entire fruit.
The fungus survives in infected plant debris and can be seed-borne, while water, wind, insects, animals, and machinery spread spores. Warm, rainy, and wet weather favor disease development and spread.

Effective Management

Cultural and biological control measures for early blight include using pathogen-free seeds, following crop rotation for at least two years, controlling susceptible weeds, and using drip irrigation instead of overhead irrigation.
Staking plants can increase airflow and reduce contact between leaves and soil. Pseudomonas gladioli B25 and Trichoderma viride can be used for seed treatment or foliar spray.
Chemical control options include Azoxystrobin 23% SC, Metiram 70% WG, Pyraclostrobin 20% WG, and Boscalid 25.2% + Pyraclostrobin 12.8% WG, which can be applied as two foliar sprays.

Septoria Leaf Spot Disease and Effective Management Strategies

Septoria leaf spot disease affects less vigorous tomato plants and is characterized by small, round to irregular spots with a grey center and dark margin on leaves.

The spots usually start on lower leaves and gradually advance upwards, eventually leading to complete defoliation of affected leaves. Stems and flowers can also be attacked, but fruits are rarely affected.
The disease survives in infected plant debris or solanaceous weeds and is spread through conidia by rain splash, wind, and sticking to hands and clothing.
High humidity and moist weather with intermittent showers at 25°C are favorable conditions for disease development. Nutrient inadequacy in the late season can also contribute to its spread.

Effective Management

Bury crop debris after harvest reduces pathogen survival and promotes rapid leaf drying by avoiding dense plantings, staking plants, and orientating rows parallel to the prevailing wind direction.
Avoid overhead irrigation, time irrigations to end before dusk, and reduce contact between foliage and soil.
Do not work in tomato fields when foliage is wet to reduce the plant-to-plant spread of the fungus.
Chemical control can be achieved by spraying the crop with Copper oxychloride 50% WP or Cyazofamid 34.5% SC.

Late Blight Disease and Effective Management Strategies

Late blight is caused by Phytophthora fungus, preferred by cold nights and humid days. The disease mainly survives in potato seed tubers and contaminated tomato transplants. Symptoms start with water-soaked spots on leaves, rapidly growing into pale green to brownish-black lesions. Lesions on the undersides of leaves can be covered with grey-to-white mouldy growth during wet weather. The disease progresses with the yellowing and browning of foliage. Lesions also occur on petioles and stem, rapidly expanding into brown to black lesions filled with mouldy growth. Infected stems and petioles can collapse, causing the death of the crop.

Effective Management

Checking transplants for symptoms before planting.
Removing infected plants to avoid spreading.
Avoiding overhead irrigation.
Using fungicides such as Azoxystrobin, Copper oxychloride, Cyazofamid, Mandipropamid, Cymoxanil, Famoxadane, and Mancozeb.
Seed infection is unlikely on commercially prepared tomatoes or thoroughly dried saved seeds.

Damping-off Disease and Effective Management Strategies

Damping-off disease is a fungal disease affecting tomato seedlings in two phases: pre- and post-emergence. Pre-emergence damping-off causes complete rotting of the seedlings before they reach the soil surface, while post-emergence damping-off infects the juvenile tissues of the collar at the ground level.

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High humidity, high soil moisture, cloudiness, and low temperatures below 24° C for a few days are favorable conditions for infection and development of the disease. Seed, soil, and water are the primary sources of survival and spread, while conidia through rain, splash, or wind are secondary sources. The only preventive measure for pre-emergence damping-off is seed treatment with Trichoderma viride, while Metalaxyl, Mancozeb, Fosetyl Al, and Carbendazim are effective management strategies.

Southern Blight Disease and Effective Management Strategies

The soil-borne fungus Sclerotium rolfsii, which infects the plant’s lower stem and thrives in hot weather with high humidity and soil moisture, is the cause of southern blight.

Symptoms: The first sign is a rapid wilting of the entire plant, then a water-soaked lesion near the soil line that quickly turns brown and girdles the stem.
Management: To manage Southern blight, crop rotation is recommended, allowing ample time to break down green manure before planting tomatoes. Trichoderma konigii can be sprayed at 2 grams/lit of water. The crop can be sprayed with Fluxapyroxad 25%+Pyraclostrobin 25% SC at 1 to 2 ml/liter or Pyraclostrobin 20% WG at 1 gm/liter of water.

Tomato Anthracnose Disease and Effective Management Strategies

Tomato anthracnose is caused by several species of fungi in the genus Colletotrichum. It infects ripe tomatoes but can also infect green and tender ones.

Symptoms on ripe fruits include round, depressed lesions with darkened centers. Anthracnose lesions often combine and contribute to large areas of rotting that make the fruit unfit for processing. Anthracnose signs first appear on the surface of the ripening fruits as thin, oval, slightly sunken lesions.
Management: Enrich the soil with organic mulches and improve drainage to protect against rain splash. Spray the crop with Tebuconazole, Azoxystrobin + Difenoconazole, Azoxystrobin + Mancozeb, or Flupyram + Tebuconazole in water.

Powdery Mildew Disease and Effective Management Strategies

Powdery mildew disease affects tomatoes and is caused by Leveillula taurica, Oidium neolycopersici, and Oidium lycopersici.

Symptoms include light-green to bright-yellow lesions, white powdery masses of conidia, and necrotic lesions that can lead to reduced yields and defoliation of plants. Avoid overcrowding seedlings, excessive nitrogen fertilizer, and moisture stress to reduce susceptibility to the disease.
Management: Spray with Azoxystrobin, Difenoconazole, Flusilazole, Hexaconazole, Kresoxim methyl, or Myclobutanil to manage the disease. Collect and dispose of infected plant material and avoid overlapping crops to prevent spores from infecting new plants. Crop rotation with non-host crops, such as root crops or those in the cabbage family, can also be effective. Sulfur-based treatments can also be used to manage powdery mildew.

Tomato Wilt Disease and Effective Management Strategies

Fusarium wilt is a disease that causes the clearing of veinlets and chlorosis of leaves in tomato plants, followed by wilting and death within a few days. It is spread through soil and implements and thrives in relatively high soil moisture and temperature.

Effective management: Avoide excessive nitrogen, crop rotation, and use calcium nitrate fertilizer instead of ammonium nitrate. Root dip or drenching with Trichoderma harzianum can also help. Seed treatment with Tebuconazole or Carboxin + Thiram is recommended.

Buckeye Rot/ Root Rot Disease and Effective Management Strategies

Phytophthora nicotianae var parasitica, capsici, and drechsleri cause buckeye fruit and root rot disease. These pathogens can survive in soil and plant debris for at least two years and spread through irrigation water and farm machinery. Moderate soil moisture and temperatures (20°C) encourage infection.

Symptoms of the disease include root and crown rot, foliar blight, fruit rot, and stem lesions.
Effective management strategies include growing tomatoes on raised beds with well-drained soil, staking or mulching plants to prevent fruit from contacting the soil and avoiding frequent irrigation. Crop spraying with Mancozeb 75% WP or Propineb 70% WP can also help manage the disease.

Verticillium Wilt Disease and Effective Management Strategies

Verticillium wilt is caused by two species of Verticillium fungi and affects almost 200 plant species. The pathogen is soil-borne and can survive for years. Infection occurs when the fungus reaches root wounds caused by intercultural interactions, secondary root forming, and nematode feeding.

Symptoms include uniform yellowing and wilting of lower leaves, younger leaves wilting and dying, stunted growth, and small fruits. Internal browning streaks of the vascular system in the stems are also present.
Management strategies include crop rotation, root dip or drenching with Trichoderma harzianum, and seed treatment with Tebuconazole or Carboxin + Thiram.

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Conclusion

Fungal diseases can cause significant damage to tomato plants, resulting in reduced yield and quality. Effective management strategies include crop rotation, disease-resistant varieties, proper irrigation and fertilization, and timely application of fungicides. Implementing these strategies can help control fungal diseases and improve tomato production.

How to Control Fungal Diseases in Tomatoes and Effective Management Strategies