Plant Pathology Infobytes

May 19, 1999
Disease Control for Tomato Early Blight

Year in and year out, gardeners who have the fewest disease and insect problems are those who start their pest control programs early in the season. A good example is early blight of tomato. This fungus disease is correctly named since it gets off to an early start following spring rains.

Early blight is generally one of the most severe tomato problems faced by home vegetable gardeners each season, and for top yields of high quality fruit, early blight control is essential. Early blight-resistant tomato varieties aren't available, so gardeners have to use a combination of disease management practices.

Early blight shows up as a leaf blight on the lower part of plants. The disease moves upward, and by early to mid-summer, early blight has caused a "firing-up" of foliage over most of the tomato plants in the garden.

As the disease progresses, leaves turn yellow, wither, and drop from plants. Tomato plant severely infected by early blight produce low yields of undersized fruit. Generally, fruit also show signs of sun-scald since leaves aren't present to protect fruit from direct sunlight.

Early blight tends to be more severe when periods of rainy weather are experienced after transplants are set. Plants are more likely to become infected by the blight fungus under these conditions.

How do you handle early blight? A management program for this disease is based on crop rotation, removal and destruction of crop debris from previous crops, staking, mulching, and timely application of fungicides.

Staking and mulching are important in an early blight control program, since staking keeps foliage and fruit from contacting the soil surface, and mulching cuts down on "soil splash" onto lower parts of the plant. Soil particles often contain the early blight fungus spores, and mulching is a good way of keeping the fungus from invading plants. Plastic, or organic mulches (pine straw or even newspapers) are equally effective.

Application of fungicides is also generally needed for early blight control. Field tests have shown that chlorothalonil, maneb, and mancozeb fungicides --- all available at gardening supply stores under a variety of trade names --- provide effective early blight control when used according to label directions and applications are started early in the season.

As an added plus, any of these fungicides may be "tank mixed" with an insecticide such as malathion or sevin, thus allowing a single application for control of disease and insects.

Begin fungicide applications as soon as possible after transplants are set out and continue at 7 to 10-day intervals throughout the season. Also, applications should be made after rainfall. Other leaf diseases such as leaf mold, gray leaf spot, and Septoria leaf spot are controlled by these fungicides.

Read and follow label pesticide directions concerning rates, application intervals, and the number of days required from the last application until fruit can be harvested.

For additional information on early blight and other disease problems, check with your County Extension Office.



Written by the late Dr. Frank Killebrew

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