8 Common Tomato Diseases: Identification, Treatment, and Prevention

Identifying and treating common tomato diseases is crucial for successful crop growth. Tomato plants are susceptible to fungi, bacteria, mildew, viruses, and fruit issues like sunscald and blossom end rot. Providing optimal conditions for healthy plants with strong disease resistance is the primary defense.

Many diseases are fungal and thrive in specific weather conditions. Excessive rain in cool or warm periods can create ideal environments. Taking proactive measures to treat your plants when adverse conditions persist can help prevent the spread of problems that become challenging to eliminate once they appear.

Implementing good gardening practices such as crop rotation, debris removal, weed and pest control, and proper irrigation can help deter infections. Despite these efforts, even the most resilient crops can fall prey to these 8 common diseases. Be vigilant for symptoms and adopt strategies to maintain the health of your tomato plants.

1.Early Blight

Early blight, caused by the Alternaria fungus, is the most common among several leaf spot diseases affecting tomatoes. Dark brown spots surrounded by rings typically begin on the lower leaves and progress upwards, leading to the eventual wilting, drying, and shedding of foliage. Lesions may also appear on stems and fruits, potentially resulting in sunscald. Early blight thrives in hot, humid conditions and can persist in the soil for up to a year.

To address early blight, remove lower leaves, including about one-third of the infected foliage. Apply a tomato-specific fungicide at the initial signs of infection or during weather conditions conducive to disease development.

Prevent early blight by watering at the soil level, using mulch, maintaining adequate plant spacing, employing stakes for support, practicing effective weed control, removing bottom leaves regularly, and implementing a two-year crop rotation for tomatoes and related nightshades.

2.Fusarium Wilt

Fusarium wilt, caused by the Fusarium oxysporum f. sp. lycopersici fungus, infects tomato plants through the roots. In warm conditions, the entire plant wilts during the day but may recover at night. Eventually, leaves on one side yellow, dry, and drop off, while the lower stem's inner tissue turns red or black. Plants can perish swiftly or succumb within a week or longer.

As there is no fungicide for fusarium wilt, infected plants must be removed and disposed of. While fungus spores can linger in the soil for years, this disease does not spread among plants within the same growing season.

To prevent fusarium wilt, opt for varieties labeled VFN or FN, denoting resistance. Maintain clean tools and implement a three-year crop rotation. Since pigweed and crabgrass host Fusarium wilt, effective weed control is crucial. Avoid excessive nitrogen fertilization, as it can promote disease development.

Tip

Verticillium wilt, although caused by a different fungus, shows symptoms almost identical to fusarium wilt. It develops in cool temperatures. Treatment and prevention are the same for both types of wilt.

3.Powdery Mildew

Powdery mildew is spread by three different types of airborne fungi. The spore type varies with temperature, but high humidity levels increase the likelihood of disease. Yellow spots on leaves transition to white powdery lesions that cover the entire leaf and spread to the stems. While fruits themselves do not develop powdery mildew, defoliation can lead to sunscald and crop loss.

To address powdery mildew, halt its spread using sulfur dust, fungicides, biofungicides, and horticultural oils. Remove infected leaves and buds, and treat the entire crop.

Prevent powdery mildew by ensuring adequate spacing between plants, pruning for improved air circulation, providing consistent hydration at soil level, and avoiding leaf wetting.

4.Anthracnose

Anthracnose is a disease that mainly affects fruits and is caused by Colletotrichum coccodes, a fungus that thrives in warm and wet environments. Fruit shows small, sunken, water-soaked spots that expand in concentric circles, leading to tomato rot. Leaves may also display small, round spots with yellow halos. Infection typically begins in immature fruits, with symptoms only appearing during ripening. This fungus can be hosted by numerous weeds and plants, surviving in soil and plant remains during winter.

Fungicides are most effective when used preventatively. Apply tomato fungicide to the entire crop at the first sign of infection or when weather conditions are conducive to disease development. Avoid leaving tomatoes to overripen on the vine.

To prevent anthracnose, stake plants, mulch, and water at soil level. Use certified seeds and plant in well-draining soil. Dispose of rotten fruit and debris, practice effective weed control, and rotate crops every two years, including other nightshades.

5.Septoria Leaf Spot

Septoria leaf spot, caused by the Septoria fungus, manifests on leaves as numerous small, dark, circular spots. While symptoms resemble early blight, septoria typically emerges during the initial fruit set. It spreads swiftly, resulting in the loss of older leaves before infecting new foliage and swiftly advancing through the entire crop. Insects, tools, and water serve as vectors for spreading fungus spores, which can persist in the soil for up to two years. Premature leaf shedding can result in fruit loss and sunscald.

The most effective approach is to manage the spread by consistently applying tomato fungicide or biofungicide to the entire tomato crop. Given that this fungus thrives in warm, moist conditions, vigilance for symptoms and prompt action are crucial.

Maintaining good garden hygiene is essential in preventing septoria leaf spot. Promptly remove fallen leaves and debris from the garden, sanitize tools before and after plant work, water at the base, and manage insect pests. Rotate your tomato crops every three years.

6.Botrytis Gray Mold

Botrytis stems from the Botrytis cinerea fungus, characterized by brown lesions on leaves and stems, along with a whitish soft rot in fruits. Infection typically originates from damaged stems or pruning cuts and can remain dormant for up to 12 weeks. This mold can lead to tomato rot post-harvest, causing leaves to wither and drop while stem girdling induces wilting. Even tomato flowers are vulnerable to this fungus. Spores are disseminated through wind and water, being most prevalent in cooler temperatures.

Botrytis commonly diminishes as temperatures increase. Address extensive or persistent infections by applying tomato fungicide or biofungicide specifically designed for gray mold.

To prevent botrytis, prune plants in the early afternoon to ensure rapid drying of cuts. Refrain from overhead watering and handling wet plants. Maintain adequate spacing between plants and rows to promote optimal air circulation.

7.Bacterial Speck

Bacterial speck, caused by Pseudomonas syringae, affects tomato plants during prolonged cool, damp conditions. Small, irregular, dark brown to black spots surrounded by yellow tissue develop near leaf edges. Mature fruit may exhibit superficial raised spots. The disease spreads through water splashing on leaves.

While bacterial speck is incurable, preventive measures involve treating plants with a copper fungicide in cool, wet weather periods. The pathogen's spread is deterred by hot weather.

To prevent bacterial speck, postpone planting until conditions are warmer and drier. Apply a protective fungicide if cool, wet weather persists. Refrain from overhead irrigation and annually rotate tomatoes and other nightshades.

8.Southern Blight

Southern blight is caused by the soilborne fungus Athelia rolfsii. More prevalent in southern regions, it favors high temperatures, moist conditions and acidic soil. Black-brown lesions appear on stems near ground level and spread rapidly forming a white mold that produces sunken brown necrotic tissue. Plants wilt and fall over and fruits that contact soil develop yellow spots that turn to watersoaked lesions. Tomatoes rot within three to four days. Southern blight can persist in soil for years.

Prevention is the best treatment for this fungus. Solarizing the soil before planting can effectively kill spores. Fungicides and biofungicides can help manage southern blight. Soil fumigants can be used but are expensive.1

Prevention steps include solarization, crop rotation, and maintaining soil pH level for tomatoes. Avoid planting during wet weather with expected high temperatures. Remove plant debris and til or disk soil several times before planting. Eliminate weeds and rotate tomatoes with non-host crops.

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