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Wednesday, July 30, 2014
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Published: Saturday, 7/16/2011

Early blight a common tomato disease

BY BARBARA NORTHRUP
SPECIAL TO THE BLADE

Questions from Blade subscribers continue to come into our office regarding problems and concerns with vegetables.

One caller was worried about brown lesions appearing on the leaves of his tomato plants. He brought a sample into our office and it was determined to be Tomato Early Blight disease.

This is one of the most common foliar diseases of tomato, a fungal infection caused by the pathogen Alternaria solani. The name "early blight" makes many gardeners think that this fungus can only infect plants during the early fall or spring; unfortunately, it can occur anytime during the growing season.

The infection results in very unique and identifiable spots often developing first on older leaves located nearest the soil, and then it spreads to younger leaves as the season progresses.

Early blight lesions are easy to diagnose due to their characteristic circular rings of infection with a target-like appearance. These leaf spots are brown and vary in size and shape. Often, several lesions overlap, causing the leaf to turn yellow or brown. The leaves dry up and fall off the plant and the defoliation usually begins at the plant base and works upward, creating a palm tree-like appearance.

The lack of foliage quickly will expose the ripening fruit to direct and excessive sunlight, resulting in sun-scald injury. The lack of foliage drastically reduces fruit quality and quantity. Although early blight primarily is a disease of the leaf, the same characteristic bull's-eye type lesions might develop on stems and fruit.

This fungus might overwinter on plant debris, seeds, or on weeds in the Nightshade family like horsenettle or black nightshade. Splashing rain, running water, and moving spreads the fungus throughout the field. Disease development is favored by abundant rainfall, high relative humidity, and warm temperatures. All of these environmental elements have been seen in our local area.

Garden sanitation is the best way to reduce the amount of fungus present that causes infections the following year. In the fall, be sure to clean up tomato plots by removing the dead plants or burying tomato debris deep into your garden. Try to avoid planting tomatoes in the same area of the garden year after year. If starting seeds, use clean, new seeds or purchase healthy transplants in the spring.

This disease might be controlled effectively using fungicides which contain the active ingredient chlorothalonil. Most garden centers will be able to direct you to the correct pesticide. Be sure to follow the directions on the label, and do not use this on other plants, unless the label specifically lists that plant.

For the best results, applications should begin as soon as symptoms begin to appear, typically around the time when the fruits are about the size of small grapes. Applications should be made every seven to 10 days, depending upon label instructions; however, severely infested plants are not likely to be rescued by fungicide treatments.

OSU Extension has FactSheets available that cover a myriad of problems you might be experiencing in your garden. These are available on line at ohioline.osu.edu, or by calling OSU Extension Lucas County at 419-578-6783 and we will be happy to mail out the items to your home. For specific information on Early Blight, check this link: http://bit.ly/cUHf2V.

Next week we will focus on soil -- don't treat it like dirt. You will be amazed at what all can be found in your soils. Some good things, and some not so good. We will point out the differences.

Barbara Northrup is an information associate with OSU Extension Lucas County. If you have questions, call the OSU Extension Master Gardener Volunteer Horticultural Hotline at 419-578-6783. Volunteers are on hand Monday, Wednesday, and Friday from 10 a.m. to 1 p.m. Questions also may be e-mailed to mghotline@ag.osu.edu and possibly answered in a future Plant to Plate column.



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