Early Blight of Tomatoes

R. Keith Collins  |  4/26/2011 1:24:56 AM

Photo courtesy of LSU AgCenter's Louisiana Plant Pathology Department.

Keith Collins is the LSU AgCenter county agent for Richland Parish. This news article appeared in  the Delhi Dispatch.

Early blight is one of the most common diseases of tomatoes in Louisiana. The pathogen can cause disease on leaves, stems and fruit but is more damaging on the leaves where it causes lesions and premature defoliation.

This disease first develops on the older leaves lower on the plant then progresses up the plant, especially during fruit production. Initial symptoms are small, dark-colored, circular lesions, often surrounded by chlorotic (yellow) tissue. As the lesions expand, concentric rings or ridges become evident within them. Left untreated, it causes leaf defoliation which exposes stems and fruit to potential damage. Symptoms on stems are oval and elongated, brown and sunken lesions with rings within them. Fruit lesions appear as sunken, dark-colored sunken spots with concentric rings within them.

Early blight survives primarily in infested debris from the previous tomato crop but may also survive on contaminated seeds. The pathogen produced in debris spread to the new crop by wind or splashing water. It spreads over a wide range of temperatures when conditions are wet and humid. Irrigating tomatoes can create these conditions.

Very few early blight resistant tomato varieties are available, so management of the disease relies primarily on cultural practices and the use of fungicides. Cultural practices include use of clean seed, crop rotation and complete removal of plants at the end of the growing season. Increasing distance between plants to improve airflow and promote drying will help.

Fungicides should be used as soon as symptoms appear. Fungicides will only protect the plant tissue that has been sprayed but should be reapplied every seven to 10 days to provide adequate protection. Fungicides containing chlorothalonil, copper hydroxide or mancozeb are recommended and should be available at local lawn and garden centers.

For further information please contact your local Extension office at 318-728-3216 or stop by at 702 Madeline St. in Rayville. Visit our website at www.lsuagcenter.com/richland or visit us on Facebook at Richland Extension.

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