HPIPM:Damping Off, Seedling Blight

Author: Howard F. Schwartz, David H. Gent, and William M. Brown, Jr.

Identification and Life Cycle

Many pathogens can cause damping-off and seedling blight of alfalfa seedlings in the High Plains region, including Pythium spp., Phytophthora spp., and Rhizoctonia spp. Other fungi that cause alfalfa damping-off such as Cylindrocladium crotalariae and Mycoleptodiscus terrestris seldom are found in the High Plains region. Damping-off is associated with cool (Pythium and Phytophthora spp.) to warm (Rhizoctonia spp.) soil temperatures and excess soil moisture. Pathogens associated with damping-off are common soil inhabitants and can survive in soil as dormant oospores or sclerotia, pathogenically on alternate hosts and weeds, and saprophytically on crop residues.

Plant Response and Damage

Damping-off can occur before or after alfalfa emergence. Pre-emergence damping-off results in a brown, gelatinous rotting within the seed coat. Radicles and cotyledons may become brown and soft after germination, but fail to emerge. Water-soaked, greasy lesions may also form on hypocotyls and roots after emergence when seedlings are infected with Pythium or Phytophthora spp., causing plants to collapse and wither. Post-emergence damping-off caused by Rhizoctonia spp. begins as elliptically-shaped, brick-red sunken cankers on roots and hypocotyls. Plants eventually become flaccid and die.

Biological Control

Kodiak (Bacillus subtilis strain GBO3) is registered for suppression of Fusarium, Rhizoctonia, and Pythium spp., but its efficacy in the High Plains is unknown.

Cultural Control

Plant high quality alfalfa seed in a firm, well-prepared seedbed at optimum pH, soil temperature, and fertility level for rapid germination and growth. Avoid compaction, poorly drained fields, and excess irrigation that can favor damping-off pathogens. High seeding rates can partially compensate for stand losses when disease is present.

Chemical Control

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.