NC State Extension Publications

Pathogen

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.

Early blight symptoms on tomato

Early blight symptoms on tomato

Inga Meadows

Early blight symptoms on tomato

Early blight symptoms on tomato

Inga Meadows

Host Crops and Plants

The currently known host range of Alternaria linariae is limited to tomato (Lycopersicon esculentum).

Host Parts Affected

The leaves, fruit, and stem may be affected by Alternaria linariae.

Blighted tomato plants due to early blight

Blighted tomato plants due to early blight

Inga Meadows

Identification

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 14 - 12-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.

Favorable Environmental Conditions for Disease

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.

Disease Transmission

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.

General Disease Management

  • 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.

Disease Control for Conventional Growers

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
boscalid Endura 0 7
chlorothalonil Bravo 0 M
cyprodinil + fludioxinil Switch 0 9 + 12
difenoconazole + benzovindiflupyr Aprovia Top 0 7 + 3
difenoconazole + cyprodinil Inspire Super 0 3 + 9
fenamidone Reason 14 11
flutriafol Rhyme 0 3
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
penthiopyrad Fontelis 0 7
pyrimethanil Scala 1 9
strobilurinR Quadris, Cabrio, Gem, Evito 0 11
R Resistance to this group of fungicides has been reported in North Carolina.

Disease Control for Organic Growers

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.

Disease Control for Home Gardeners

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.

Additional Resources

Author:

Extension Associate, Vegetable Pathology
Plant Pathology

Publication date: Dec. 11, 2015

The use of brand names in this publication does not imply endorsement by the North Carolina Cooperative Extension Service of the products or services named nor discrimination against similar products or services not mentioned.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.