Disease guide

Pythium spp., Rhizoctonia solani, Fusarium

Pre-emergence Damping-Off: Seeds may rot before germinating or seedlings may die prior to emergence.

Post-emergence Damping-Off: Young seedlings develop a rot at the crown. Later, the tissue becomes soft and constricted, and the plants wilt and fall over.

Pythium spp.: This fungus is the most common cause of pre-emergence Damping-Off. Typical symptoms include dark-brown to black, water-soaked lesions that rapidly spread over the entire seedling. Brown, water-soaked lesions that start on the roots and later extend up the hypocotyl characterize post-emergence Damping-Off. Eventually, the lesions girdle the hypocotyl, causing seedlings to wilt and die. The root cortex becomes macerated and easily sloughs off.

Rhizoctonia solani: Pre-emergence symptoms include reddish-brown lesions on hypocotyls and death of growing tips. Post-emergence Damping-Off is characterized by reddish-brown to black lesions that develop on roots and hypocotyls at or below the soil line. Later, hypocotyls collapse and seedlings wilt and die.

Fusarium spp.: Dark-brown lesions on hypocotyls characterize pre-emergence Damping-Off. Postemergence Damping-Off is characterized by dark-brown lesions on roots and hypocotyls at or near the crown. Lesions eventually girdle hypocotyls, killing the seedlings. Root lesions become soft and water-soaked.

These fungi have a wide host range and can survive for long periods in soil, plant debris and weeds. Damping-Off is generally most severe under conditions of high soil moisture and/or compaction, overcrowding, poor ventilation and cool, damp, cloudy weather. Water-splashing moves infested soil from diseased to healthy plants.

Improving drainage and moisture regulation to help prevent soil saturation reduces Damping-Off. Fungicidal soil drenches and seed treatments are available that help manage Damping-Off. Rotation to cereal crops and soil fumigation or solarization may help reduce Damping-Off in the field. Use pasteurized soil mixes in nurseries.