Most seedlings are particularly susceptible to damping-off. In general the disease is caused by the fungi Pythium but some damage also occurs from infection from Rhizoctonia solani. These fungi are found in soils and is not confined to any region.
Pre-emergence of damping-off
Pre-emergence of damping-off occurs when the seed is infected with the fungi which results in poor stands. Post emergence damping-off occurs after the seedlings have emerged from the seedbed, but while they are still your and small. The roots may be killed and affected plants show water soaking and shrivelling of the stems at the ground line. They soon fall over and die. Damping-off usually occurs in small patches at various places in the seedbeds and increase in size from day to day until the seedlings reach such a size that they are no longer susceptible to attack.
Post emergence of damping-off
The most critical stage is two weeks after the seedlings emerge. As the stem hardens and increases in size, the injury no longer occurs. Some seedlings are not killed immediately but their roots are severely damaged and the stems are girdled at the ground line. Such plants remain stunted and often to not survive transplanting.
High moisture content of growth medium increases the risk of damping-off. Irrigation scheduling is crucial during the seedling stage to reduce the development of the fungi. The risk of damping-off can significantly be reduced if the seed trays are sterilized before use.