Early blight of tomato is caused primarily by the fungus Alternaria linariae (=A. tomatophila; formerly known as A. solani), although other species of Alternaria may be isolated from lesions.
The currently known host range of Alternaria linariae is limited to tomato (Lycopersicon esculentum).
The leaves, fruit, and stem may be affected by Alternaria linariae.
Symptoms of early blight can occur on the foliage, fruit, and stem at any stage of development. The disease is more commonly observed in the field, however, seedlings in the greenhouse can be affected by collar rot (also caused by species of Alternaria).
Lesions first develop on lower leaves as small, brownish-black spots which can expand to about 1⁄4 - 1⁄2-inch in diameter with characteristic concentric rings in the darkened area. The area surrounding the lesions may become yellow and, as disease progresses, the entire leaf may turn yellow. In later stages, lesions may appear in the upper leaves and defoliation may occur in the lower part of the plant leaving the fruit susceptible to sunscald.
Fruit may become infected through the calyx around the stem attachment and are susceptible in the green or red stage. Lesions can expand to cover the entire fruit and are typically sunken, leathery, and dark brown to black with concentric rings.
Spores may be abundant on lesions on any part of the plant.
Disease is favored by warm temperatures and moderate to heavy rainfall.
The fungus can survive between seasons on crop debris in the soil. Volunteer tomato plants also can be a primary source of inoculum.
Spores of Alternaria linariae are primarily spread by wind, air currents, and water splash. The fungus survives in plant debris in soil and, in milder climates, can survive on volunteer tomato plants.
- Maintain plant vigor. Maintaining adequate fertilization and improving host vigor can reduce susceptibility to early blight.
- Remove volunteer weeds. Removing volunteer tomatoes can reduce disease as they can serve as an inoculum source.
- Rotate every 2-3 years. Rotating away from tomato can reduce inoculum density in a field.
- Plant tolerant varieties. There is no resistance to early blight, however, some varieties are more tolerant to the disease.
- Apply fungicides preventatively.
In addition to the cultural practices listed above, there are several products that are effective at controlling the disease. For the latest fungicide recommendations for early blight, consult the Southeastern US Vegetable Crop Handbook.
Example products for control of early blight in tomato.
|Active Ingredient||Example Product||PHI (days)||FRAC Group|
|azoxystrobin + chlorothalonil||Quadris Opti||0||11 + M|
|azoxystrobin + difenoconazole||Quadris Top||0||11 + 3|
|cyprodinil + fludioxinil||Switch||0||9 + 12|
|difenoconazole + benzovindiflupyr||Aprovia Top||0||7 + 3|
|difenoconazole + cyprodinil||Inspire Super||0||3 + 9|
|fluopyram + trifloxystrobin||Luna Sensation||3||7 + 11|
|fluopyram + pyrimethanil||Luna Tranquility||1||7 + 9|
|fluxaypyroxad + pyraclostrobin||Priaxor||7||7 + 11|
|mandipropamid + difenoconazole||Revus Top||1||40 + 3|
|strobilurinR||Quadris, Cabrio, Gem, Evito||0||11|
|R Resistance to this group of fungicides has been reported in North Carolina.|
For organic control, the cultural control measures described above are the best means of control.
Several copper-based fungicides can reduce the severity of disease. Consult the Organic Materials Review Institute (OMRI) pesticide list for approved products.
In addition to the cultural practices mentioned above, home gardeners may reduce disease by the following.
- Trellis tomatoes to increase air flow and to prevent spores splashing up from the soil.
- Use a mulch to prevent spores from splashing up onto plants.
- Prune the bottom most leaves as the plant grows. These leaves are usually more infected than the upper parts of the plant.
- The NCSU Plant Disease and Insect Clinic provides diagnostics and control recommendations
- The Extension Plant Pathology Portal provides information on crop disease management
- The Southeastern US Vegetable Crop Handbook provides information on vegetable disease management
- The USDA Fungus-Host Distributions Database provides information about reported hosts for plant pathogenic fungi and oomycetes
Publication date: Dec. 11, 2015
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