What is Damping Off

"Damping-off" is a single, collective term used to describe underground, soil line, or crown rots of seedlings due to unknown causes.  Many soil borne diseases and fungi can cause these symptoms of sudden plant death.  Some of the more common causes are listed below.

Pythium Root Rot (Pythium spp.) - Similar to Rhizoctonia in that it causes both damping-off as well as foot rot in plant cuttings.  However, infection occurs in cool, wet, poorly-drained soils, and by over-watering.  Infection results in a wet odorless rot.  Species of Pythium can survive for several years in soil and plant debris.

Phytophthora Root Rot (Phytophthora spp.) - Usually associated with root rots of established plants but are also involved in damping-off in seedlings.  These species enter the root tips and cause a water-soaked brown to black rot similar to Pythium.  Survives indefinitely in soil and plant debris.

Rhizoctonia Root Rot (Rhizoctonia solani) - A fungi which causes damping-off of seedlings and foot rot of plant cuttings. Infection occurs in soils with warm to hot temperatures and moderate moisture levels. The fungi is found in all natural soils and can survive indefinitely. Infected plants often have slightly sunken lesions on the stem at or below the soil line. Transferring this fungi from nature to your germination area or greenhouse is as simple as using the same tools out of doors as you do in. Do not use your germination area to mix potting soils or transplanting seedlings using soils. Cleanliness is key here. There are also other miscellaneous fungi which cause similar symptoms. These include Sclerotinia (white mold), Sclerotium rolfsii, Macrophomina phaseoli, some species of Botrytis (gray mold), Aphonomyces, Fusarium, and Cylindrocladium.

Preventative measures include:
• Utilizing sterile, soiless mixes for seed starting and rooting of cuttings.
• Sterilize tools, trays and pots with a 10:1 ration of water and household chlorine bleach.
• Provide adequate airflow and ventilation in the germination area using fans if necessary.
• Provide optimum soil temperatures for the plant variety that you are germinating.
• Avoid over watering and bottom watering. Saturate the soil but allow good drainage and apply no more water until just before the plants approach wilt stage.

Additional Information:
Damping-off of seedlings - University of Minnesota Extension