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Extension > Garden > Commercial fruit and vegetable production > Plant diseases > Early blight of tomato

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Early blight of tomato

Anna Johnson, Michelle Grabowski and Angela Orshinsky

Importance

Early blight is one of the most common tomato diseases, occurring nearly every season wherever tomatoes are grown. It affects leaves, fruits, and stems and can be severely yield limiting when susceptible cultivars are used and weather is favorable. Severe defoliation can occur and result in sunscald on the fruit. Early blight is common in both field and high tunnel tomato production in Minnesota.

M.Grabowski, UMN Extension

Leaf spot symptoms of early blight on tomato.

Host and pathogen

Early blight can be caused by two different closely related fungi, Alternaria tomatophila and Alternaria solani. Alternaria tomatophila is more virulent on tomato than A. solani, so in regions where A. tomatophila is found, it is the primary cause of early blight on tomato. However, if A. tomatophila is absent, A. solani will cause early blight on tomato. Both pathogens can also infect potato, although A. solani is more likely to cause potato early blight than A. tomatophila. Both pathogens can also infect eggplant and several Solanaceous weeds including black nightshade (Solanum ptycanthum), and hairy nightshade (Solanum physalifolium)

Identification

Signs and symptoms

Leaves

Stem

Fruit

Environment

M.Grabowski, UMN Extension

Early blight fruit rot symptoms.

Biology and disease cycle

Alternaria tomatophila and A. solani overwinter in infected plant debris and soil in Minnesota. The pathogen also survives on tomato seed or may be introduced on tomato transplants. Lower leaves become infected when in contact with contaminated soil, either through direct contact or through rain-splashed soil. Spores can germinate between 47 and 90 F and need free water or humidity of 90% or greater. Spores infect plants and form leaf spots as small as 1/8 inch diameter and in as little as five days. Spores can be spread throughout a field by wind, human contact or equipment, resulting in many reinfection opportunities throughout a growing season.

Management

Resistant cultivars.

There are many resistant tomato cultivars available, often designated with an "EB" in seed catalogs. There is also an extensive list of resistant cultivars on Cornell University's vegetable pathology website. Resistant varieties are not immune to early blight. Rather moderate levels of resistance to either leaf infection, stem infection or both are present.

A few common cultivars with early blight resistance include:

Cultural control

M. Grabowski, UMN Extension

Early blight stem infection.

Chemical control

Below is a partial list of fungicides available for control of early blight on tomato. Applications should be made when environmental conditions favor disease to be the most effective and repeated according to label instructions.

It is important to alternate between different chemical families to avoid the development of pathogen insensitivity to particular active ingredients. Some insensitivity to the chemical family 11 has become more common in some areas, so particular care should be taken to rotate these with other chemical families. Also, if insensitivity is already present in a given field population of early blight, fungicides in chemical family 11 will not provide good control.

Active ingredient Common product names Chemical family Comments
Penthiopyrad Fontelis 7 Very good
Boscalid Endura, Lance WDG 7 Very good
Pyraclostrobin Cabrio 11 Very good, but insensitivity is becoming more common
Fenamidone Reason 11 Very good, but insensitivity is becoming more common
Azoxystrobin Quadris 11 Very good, but insensitivity is becoming more common
Cymoxanil and Famoxadone Tanos 27 and 11, respectively Good, but insensitivity is becoming more common
Fluxapyroxad and Pyraclostrobin Priaxor 7 and 11, respectively Good, but insensitivity is becoming more common
Pyrimethanil Scala 9 Good
Difenoconazole and Cyprodinil Inspire Super 3 and 9, respectively Good
Mancozeb Dithane, Manzate, Penncozeb M Good
Mancozeb and Zoxamide Gavel M and 22, respectively Good
Difenoconazole and Mandipropamid Revus Top 3 and 40, respectively Good
Cyprodinil and Fludioxonil Switch 9 and 12, respectively Good
Chlorothalonil Bravo, Echo, Equus M Fair
Copper (copper hydroxide, copper oxychloride, etc.) Kocide 2000, Champ Formula 2, Nu-Cop 50DF, C-O-C-S WDG M Fair. Some copper products OMRI listed – copper is best option for organic production

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the University of Minnesota Extension. A pesticide label is a legal document. Always follow the pesticide label directions attached to the pesticide container you are using. The site of use or plant to which the pesticide is to be applied must be listed on the label or the pesticide cannot be used. If a pesticide label prohibits use within a greenhouse, it cannot be used in a greenhouse or high tunnel in Minnesota. Remember, the label is the law.

2015

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