Damping off is caused by several soil fungi including Pythium, Fusarium and Phytophthora species, and Rhizoctonia solani.
Seedlings affected by damping off may fail to emerge (can be mistaken for poor germination of seeds). Above ground symptoms of seedlings include brown water soaked areas at the base of stems which causes the seedling to fall over and die. Roots of these seedlings are rotten.
Damping-off pathogens are soilborne and are ubiquitous even in small amounts of soil and dirt. They can be found in dirt that is stuck to reused seed trays and benches. After planting in reused trays infected with damping-off, fungal spores (mycelium) will start to colonize the soil in the trays and subsequently the seedlings. Chances of damping off in seedlings increase when seedlings are kept very wet. Some damping-off pathogens, like Pythium, have motile spores that can swim in a film of water. If seedling trays are standing in water the spores can move through the water to other seedlings.
The two most important management options are sanitation and seed treatments with fungicides.
- Sterilize reused pots and trays. If pots and trays are re-used they should be sterilized with a 10-15% bleach solution for one hour and then rinsed with clean water to remove chloride residue.
- Clean and disinfect greenhouse benches. Benches should be cleaned and disinfected with bleach.
- Place plastic under pots and trays that are on the floor. If trays or pots are placed on a dirt floor put plastic under the pots to prevent contamination from damping-off pathogens on the ground.
- Treat seeds with fungicides. This reduces the chance of young seedlings becoming infected with dampingoff pathogens.