Prevent Damping-Off Fungi

Author: Master Gardener Pat Green

The holidays are over and the seed catalogues are coming on a daily basis. Surely spring cannot be far behind. Those of us who enjoy starting our plants by seed are feeling the itch to get tarted.

One of the first problems of the season is a disease known as pre-emergence or post-emergence damping-off. Fungi in the soil attack seeds and seedlings as they begin to grow and germinate. Pre-emergence occurs when the seed or seedling dies before it reaches the surface. Post-emergence occurs when the seedling emerges and grows to a height of an inch or two, then wilts and dies. Occasionally, plants that are attacked by these fungi do not die but are stunted and may die later. Several fungi can cause this disease, including Rhizoctonia solani, Pythium spp., Phytophthora spp., Sclerotinia spp., and Botrytis spp. Most of these fungi can also cause cuttings to rot. These fungi are found in practically all soils. Older plants are seldom killed by damping off fungi mainly because the development of secondary stem tissue forms a protective barrier and limits fungal penetration.

With all that said the best control for this problem is prevention.

• Prevention starts with good sanitation. Use clean containers and tools. If necessary, disinfect with a 10% bleach solution.
  
• Use a soil less growing mixture containing perlite and vermiculite. A 50-50 mix works well.
  
• Use only clean non-recycled water on seeds.
  
• Place seed trays on clean, sterilized benches if growing in a greenhouse.
  
• Remove any trays with damping-off immediately.

Another way to help prevent this disease is to encourage the seeds to germinate and grow as fast as possible. Plants are only susceptible to damping-off as seedlings.

• Adequate light and heat to germinate and grow seedlings quickly.
  
• Bottom heat may speed germination.
  
• Avoid planting seeds too deeply.

Keep conditions in the seeding trays less favorable to the fungi. These fungi like wet conditions.

• Use well-drained planting media.
  
• Sow seeds thinly to allow air to circulate between seedlings.
  
• Promptly thin over crowded containers.
  
• Avoid excessive watering. Water from below. Keep soil on the dry side.

When considering any chemical measures be aware that many plants may be adversely affected by fungicides. Fungicide treated seeds are available. There is much current research on planting media that suppresses these fungi.
When seedlings emerge remove any plastic covering or lid that was used to increase humidity. Proper watering is important. Don't allow seed trays to stand in water. Allow soil surface to dry if using a potting soil. Do not over fertilize. A half strength water soluble fertilizer used when the second true set of leaves appear is sufficient.

If even one of your seedlings exhibits signs of damping-off, remove it and its immediate neighbors from the container at once.

Transplant your seedlings as soon as the first set of true leaves appear. A 50-50 mixture of potting soil and perlite will help keep your soil draining well and keep your plants healthy.

An excellent resource for all your seed starting is From Seed to Bloom by Eileen Powell available at your local book store or Amazon.com.

Wishing you a good gardening year in 2006.