Damping off disease of seedlings occurs worldwide in all kinds of soils. These soils are filled with microorganisms. Some are beneficial to the seedling and some are pathogenic. These organisms are activated by the presence of the plant and the substances released by its roots. These pathogenic organisms invade the root directly or through wounds and move into the cortical tissues or on into the vascular system. These pathogens release enzymes which degrade the seedling tissue and disrupt normal plant growth processes. Damping off can affect seeds and seedlings of all kinds of plants such as vegetables, flowers, field crops, fruit, and trees. Losses vary considerably with soil temperature and moisture. Most of these pathogens are favored by low temperature and high soil moisture. Favorable conditions result in poor germination and poor emergence. Seedlings often die after emergence, but the most vulnerable period is from germination to emergence. Symptoms of seed infection include failure to germinate, becoming soft, turning brown, eventually shrinking and disintegrating. Infection of seedlings, under the soil, before emergence is dark, and water-soaked. The infected area enlarges, the invaded cells collapse, and the seedling dies shortly after, without emerging. Seedlings that have already emerged are attacked at the roots and on the stem at the soil line or below.
The infected areas become water soaked and discolored. As the cells collapse, the lower part of the stem can not support the upper part of the seedling, and it falls to the ground. Once the fungus girdles the stem, the seedling dies and dries up.
Damping-off can be controlled with water control and fungicide treatments. Over- watering tends to encourage damping-off. Add only enough water to seedlings to prevent wilting. Water in the morning and allow to dry before night. When seedlings begin to damp-off, they should be given as much light as possible. Sterilization of the soil before planting is one of the most satisfactory means of preventing loss of seedlings in garden areas. Small lots of soil can be baked for 3 to 4 hours in a 160 oF oven to kill the damping-off organisms. It can also be controlled to a large degree by seed treatments and soil drenches. Use fungicides at rates recommended on the label. Fungicides considered as good soil drenches include Captan, Thiram, and Terraclor. In many cases, seed treatment alone is sufficient to protect plants from damping-off.