Damping-Off and Seedling Blight

Text adapted from Turfgrass Pest Management: A Guide to Major Turfgrass Pests in Oklahoma. Oklahoma Cooperative Extension Service.

CAUSE: Damping-off and seedling blight are collective terms applied to several seedling diseases, including those caused by species of Pythium, Fusarium, Drechslera, Bipolaris and Rhizoctonia.

HOSTS: All turfgrasses.

SYMPTOMS: When environmental conditions favor the growth of pathogens more than the germination of seeds, the pathogens can cause decay and death of seed prior to seedling emergence (preemergence damping-off). If conditions are less favorable for the pathogens, the seed may germinate to produce a weak seedling that may then be attacked and killed after seedling emergence (postemergence damping-off). In the latter case, the seedlings usually become water soaked, turn yellow to brown and finally collapse. The end result is thin stands or irregular patches of dying turfgrass.

DISEASE CYCLE: Pathogens capable of causing seedling diseases are likely to be present in all seedbeds, except those that have been fumigated. They should be assumed to be present wherever seed is planted. When pathogen growth is active and seedling growth is slow, pathogens attack and easily kill entire plants. Fungus-infected seed lots are particulary prone to diseases, because the pathogens are in an ideal location to attack at the very beginning of seedling development.

FACTORS FAVORING DISEASE DEVELOPMENT: The development of Pythium damping-off is usually favored by cool, wet conditions, while species of Rhizoctonia, Bipolaris, Drechslera and Fusarium are usually most serious during warm, wet weather.

CONTROL: Provide good surface and subsurface draining and aeration in the seedbed. Avoid planting in areas where air movement is limited due to trees, shrubs, or other barriers. Plant seeds at the recommended depth when the soil is cool and dry. Very high seeding rates should be avoided, because exceptionally dense seedling stands are generally more susceptible to these diseases. Ensure that seed/soil contact is good so that germination will be rapid. Avoid overwatering the new seedbed. Several excellent fungicides are available for use as seed treatments or soil drenches to control seed decay and as foliar sprays or soil drenches to control seedling blights.