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.