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Seedling Disease

Cool, wet seedbed conditions are ideal for many soil pathogens. As a result, fungal pathogens that may not cause problems in drier conditions will invade young seedlings. We have seen plenty of cases of seedling blights on corn at the Plant Clinic this year and expect to see the same on vegetable and flower seedlings.

All species of plants grown from seed are susceptible to one or more of the soil-borne fungi capable of causing damping-off of seedlings. Both in the field on direct-seeded crops and in the greenhouse during the production of transplants, damping-off can be a seri-ous problem. Plants wilt and die suddenly, sometimes before emerging from the soil (preemergence damping-off) and sometimes after emerging from the soil (postemergence damping-off). Symptoms can include root rot, stem lesions, and general seedling wilt.

It is well worth the money to use high-quality seed that will germinate quickly and allow plants to establish rapidly. (Mature seedlings are more resistant to seedling blights than are young seedlings.) If possible, buy seeds or transplants certified as disease free. Many commercially produced seeds are treated with broad-spectrum fungicides, such as captan or thiram, to help protect the seeds and young seedlings from fungi. This protection lasts only for a week or two after planting. Because the weather has remained cool and wet for over three weeks, even the treated seed may have problems.

Choose a planting site that is well drained and without a history of seedling disease problems. Plant when soil temperatures and moisture conditions favor quick germination and plant growth. Using raised beds may help improve soil drainage and increase soil temperatures to allow rapid growth.

Fungicides, applied at planting or transplanting, are registered for controlling seedling diseases on such vegetable crops as snap beans, peas, and peppers. The Illinois Commercial Landscape and Turfgrass Pest Management Handbook, 1998-1999 lists treatments, by host, for many ornamental plants. Homegrowers can consult Illinois Homeowners’ Guide to Pest Management. As with most disease control, the fungicide treatments of seeds are intended to protect against the damping-off fungi. You cannot wait for the problem to occur before you treat.

Further information on damping-off diseases is available in Report on Plant Diseases No. 615--Damping-Off and Root Rots of House Plants and Garden Flowers, as well as No. 916--Damping-Off and Seedling Blights of Vegetables.

Author: Nancy Pataky


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