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Early Blight of Tomatoes



Information
Common Name | Scientific Name | Geographic Distribution | Symptoms and Signs | Disease Cycle | Host
Control
Sampling | Control Strategies


Information

Common Name:

English: Early blight of tomatoes.
Spanish: Tizón temprano.

Scientific Name:

Alternaria solani (Ell. and Mart.) Jones and Grout.
(Class: Deuteromycetes, Order: Monilialales, Family: Dematiaceae)

Geographic Distribution:

World wide.

Symptoms and Signs:

The fungus infects stems, leaves and fruit of tomatoes. It may girdle seedlings causing damping-off in the seedbed. On the leaves, brown circular spots are often surrounded by a yellow area. Leaf spots have characteristic dark concentric rings. Leaf spots usually appear on the oldest leaves first and progress up the plant. As the disease progresses, the fungus may infect the stems and fruit. The spots on the fruit look similar to those on the leaves--brown with dark concentric rings. Dark, dusty spores are produced in concentric rings. The spores can be seen if the spot is touched to a light-colored object.

Disease Cycle:

The fungus can survive in soil and in infested crop and weed residues. It may be seed-borne and carried by wind, water, insects, workers and farm equipment. The spores that land on tomato plants will germinate and infect the leaves when they are wet. Spores can enter the leaf, steam or fruit. The fungus is most active during mild to warm temperatures and wet weather. The disease is worse during the rainy season. Early blight is most severe on plants stressed by a heavy fruit load, nematode attack, or low nitrogen fertility.

Host:

Tomato, potato, eggplant, green pepper, hot pepper and other plants of the solanum family.

Control

Sampling:

The best way to manage the disease is on a preventive basis. Once early blight is established in the crop, it is very difficult to control. Inspect the crop twice a week for plants with disease symptoms before initiating the fungicide application.

Control Strategies:

IPM Strategies:
Planting season
It is preferable to plant tomatoes in the dry season when the incidence of early blight is lower.
Plot location
It is better not to have multiple plantings in the same area because old crops will serve as inoculum of early blight for the new plantings. Select plots surrounded by grasslands because they are not a host of this disease.
Windbreaks
Plant windbreaks of fodder grasses such as Napier (elephant grass), or more permanent fruits trees such as mango, fig, banana or mulberry.
Irrigation
Avoid the use of overhead irrigation. If overhead irrigation is used, then apply it early in the day to allow time for the crop to dry.
Seed quality
Use disease-free certified seed. This can be bought from reputable seed merchants. Ensure the seed is in the original seed packet.
Seedlings
Seed-beds should be distant from old plantings. It is important to use new deep soil that has good drainage properties for the seed-beds. Sterilize the soil with hot water or ashes to eliminate the fungi from the soil. Inspect seedlings for any sign of disease and discard and destroy any that are suspected of being infected.
Fertilization
Increase the organic matter in the soil as much as possible, especially by using old manure and maize stalk. This will increase fertility and decrease nematodes. The use of nitrogen fixing legumes in the crop rotation scheme can also increase the fertility of the land and eliminate some of the inoculum.
Remove unharvested plant parts
Destroy tomato plant and crop debris as soon as the crop is finished. Make a compost heap and cover it with a layer of soil. Do not use this compost on tomato or any susceptible crops.
Rotation
Rotate crops by not planting tomatoes, potatoes, peppers, or eggplant in the same land for at least two, and preferably three, years.
Chemical control:
Pesticide recommendations
You need to contact the local authorities for the specific pesticides to use in your country. Remember, you must use only fungicides that are legal to use for this pest and crop in your country. When early symptoms of the early blight are detected in the field, apply protectant fungicides (carbamates, clorotalonil, cuprics); use seven day intervals when the weather is cool and damp, and up to ten day intervals if the weather is dry. Overhead irrigation and rainfall will wash the fungicide off. They should be applied after an irrigation cycle and may have to be reapplied after a heavy rainstorm.
Spray techniques
Sprays should be applied using a knapsack sprayer which is in good condition. It should be fitted with a hollow cone nozzle. The applicator should walk slowly down the rows covering the whole plant. Enough spray must be applied to coat the plant thoroughly, but the spray must not run off the plant.

References:

Dillard H, D. Cole, T. Hedges, A. Turner, D. Utete, B. Mvere, Agubba and P. Wilkinson. 1995. Early Blight of Tomatoes. Zimbabwe. Horticultural Crops Pest management. NYSAES, Geneva NY. 2 pp.
Castaño-Zacata J. and L. del Río Mendoza. 1994. Guía para el Diagnóstico y Control de Enfermedades en Cultivos de Importancia Económica. 3ra. Edición. Zamorano, Honduras: Zamorano Academic Press. 302p.

Credits:

Technical content
Alfredo Rueda and Anthony M. Shelton
Production
Ben Shelton, Cathy Weeden, and Linda McCandless
Pictures
From the Archives of the Integrated Pest Management Program at the New York State Agricultural Experiment Station in Geneva.

Contact Form:

For more information regarding this publication, contact Alfredo Rueda (aar4@cornell.edu). You may also contact one of our collaborators in your geographic region that may have more specific technical information on the topic.

Your contributions are important to us

In most cases, farmers and practitioners are the real innovators in pest management. If you have made an improvement or a new system to control this pest we will be happy to publish it here. Please send a description of your discovery to Alfredo Rueda (aar4@cornell.edu).

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    This document last modified 12/4/95 at 8:39PM EST
    If you have questions or comments about this page, please send e-mail to Alfredo Rueda (aar4@cornell.edu)