Early Blight of Potato

Early Blight of Potato

Early blight is a common and sometimes serious disease of its two major crop hosts, Potato and Tomato. The disease is caused by Alternaria solani Sorauer. The fungus has worldwide distribution and infects many types of solanaceous plants, both cultivated and weeds. A. solani overwinters as chlamydospores on crop debris in or on soil and on tubers and seed. In warmer climates it can also survive on volunteer plants as well as weed hosts. Early blight is generally develops on mature plants. Conidia serve as primary inoculum and infect plant material directly through the cuticle. All aerial plant parts including tomato fruit may become infected. Exposed tubers are also susceptible although wounding is necessary for infected on older tubers with well developed skin. Disease development is favored by mild(24-29^oC), rainy weather although it can develop at higher temperature. conidia develop lesions on the host. Profuse sporulation occurs when heavy dews or rain are present. These conidia serve as secondary inoculum and are disseminated by wind, running water, insects, field workers and implements. The disease progresses most rapidly when alternating periods of dry and wet weather occur. It is also more severe on plant under stress and significantly milder on plant grown under conditions of high soil fertility.

Symptoms

Symptoms progress from lower to upper leaves. Leaf spots begin as small brown areas. These areas enlarge and are surrounded by a border of yellow host tissue. As the spots mature, concentric rings of raised and depressed brown tissue are evident. Heavily infected plants often become defoliated. On tomato, this often results in sunscalded fruit. Tomato fruit, both green and ripe, may also become infected with the fungus. Infection generally begins at the calyx end. Brown leathery areas are formed at infection sites. They contain the same concentric rings found in leaf spots. A mass of black spores may be evident on fruit lesions when ideal weather conditions exist. Tuber lesions are characterized by dark, sunken lesions that are circular or irregular in shape. Lesions are bordered by raised area of tissue that has a blue-black to purplish discoloration. The flesh below the lesion is brown and has a corky or leathery texture. Lesions may continue to develop in storage and tubers may become shriveled. In less common instances, young plants, primarily tomatoes, may be affected. Stem infections on this plants may girdle the stem, causing premature death.

Plant Health Management

Use disease resistant or tolerant cultivars.

Crop Rotation.

Apply foliar fungicides.

Many fungicides are labeled for control of early blight. The list includes products containing mancozeb, maneb, and chlorothalonil (1997).

Make sure tubers mature in the ground before digging.

Control weeds.

Maintain vigorous plant growth.

References

Hooker, W.J.,ed. 1981. Compendium of potato diseases. American Phytopathological Society. St. Paul, MN. 125 pp.

Jones, J.B., Jones, J.P., Stall, R.E. and T.A. Zitter, eds. 1991. Compendium of tomato diseases. American Phytopathological Society. St. Paul, MN. 73 pp.

Sherf, A.F. and A.A. Macnab.1986. Vegetable diseases and their control, 2^nd ed. John Wiley & Sons, New York, NY. 728 pp.

Useful Links

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Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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