This fungus disease can be the bane of the inexperienced seed starter and comes in several guises. The best known type of Damping Off first manifests itself as a fuzzy whitish mold on the surface of the soil and then goes on to girdle the succulent stems of newly germinated plants. These develop shrunken black stems and eventually fall over and die, though the stem may remain upright for a while afterward. This type of Damping Off mainly affects very small seedlings and becomes is less of a problem as they get older and their stems get tougher. Other kinds of Damping Off kill the seed before it germinates, or rot the roots, causing the tops to turn yellow and die. Almost all soil contains the spores of Damping Off so commercial growers often avoid soil in their mixes, or sterilize it with heat or chemicals. Fortunately such techniques aren’t really necessary for the home grower. The best defense against Damping Off is to avoid giving it the growing conditions it needs. It shouldn’t be a big problem if you take the precautions outlined below. You may lose a few plants occasionally, but so what. Damping Off is mostly a disease of indoor seed raising. Growing your seedlings in a well ventilated, cool greenhouse will produce far fewer problems with Damping Off. However, if your climate dictates that you start your seedlings inside then you have a potential problem. Damping Off fungi need high humidity, so thin your seedlings promptly to prevent overcrowding, avoid overwatering (especially on cool sunless days when water doesn’t evaporate quickly) and make sure there is good ventilation and air circulation. Sulfur powder, or a tea of Seaweed, Garlic or Chamomile has been used to treat small areas of infection and prevent it spreading. Covering the seeds with compost or Sphagnum Moss (instead of sowing mix) may also help.
Photo: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org