Click to enlarge.

Beginner

Scientific Names
Phytophthora spp., Pythium spp., Rhizoctonia spp.,  Fusarium spp.

Identification

• Seedlings affected by damping-off generally rot at ground level and topple over
• Other symptoms may include seed decay, rotting roots and cankers on lower petioles
• On older plants, stem lesions and root rots are typical symptoms, causing stunting, wilting or plant death

Often Confused With
Wireworm damage
Cutworm damage

Period of Activity
Plants can be  infected by damping-off pre-emergence, during the seedling stage, or after transplanting.

Pythium and Phytophthora infections are more likely in cool, wet soils, while Rhizoctonia and Fusarium prefer warmer, drier conditions.

Scouting Notes
While walking fields, look for wilted or stunted plants or gaps in the plant stand where the transplants have died.  Dig around the plant, inspecting the lower stem and the roots to look for lesions or rots.  Record the percentage of the field impacted by damping-off or root rot.

Thresholds
None established.

Advanced

Scientific Names: Phytophthora spp., Pythium spp., Rhizoctonia spp.,  Fusarium spp.

Identification
Damping-off can occur before the plant emerges or soon after emergence, or can damage older plants after transplanting.

Post-emergence damping-off is characterized by seedlings that wilt and fall over.  On larger plants, sunken, dark lesions may develop on the stem or a rot of the feeder roots may occur, resulting in a stunted or wilted plant or plant death.

Pythium generally causes symptoms below the soil line, while Rhizoctonia and Fusarium symptoms are more often at or above the soil surface.  Pythium and Phytophthora cause damage in cool, wet soils; Rhizoctonia and Fusarium prefer warmer, drier conditions.

Often Confused With
Wireworm damage
Cutworm damage

Biology
These pathogens are present in soils and have wide host ranges.  The optimum temperature for Phytophthora and Pythium infections is 15- 20°C (59- 68°F).  Rhizoctonia infects at an optimum temperature of 32°C (90°F).

Period of Activity
Plants can be infected by damping-off before emergence, during the seedling stage, or after field establishment.  Damage from these pathogens may be worse if the crop experiences stressful growing conditions.

Scouting Notes
While walking fields, look for wilted plants and/or gaps in the plant stand where transplants have died.  Dig around the plant, inspecting the lower stem and the roots to look for lesions or rots.  Record the percentage of the field impacted by damping-off or root rot.

Thresholds
None established.

Management Notes

• Heat damage to the stem caused by exposure of the fresh transplant to high temperatures from the soil or plastic mulch may resemble stem disease.
• These pathogens often infect tissue damaged by extreme temperatures, wind whipping, sandblasting or rough handling.  Infections are common on stressed transplants, such as those held back or stored for a period of time before transplanting.