Damping off: Pythium seed rot
Pathogen: Pythium irregulare
Symptoms
Seeds water-soaked, mushy and decomposing; infected roots are gray and water-soaked; seedlings that have already emerged prior to infection collapse and die; older plants that become infected become severely stunted.
Disease development
The fungi that cause damping-off are usually common in an onion production field. These fungi generally survive for long periods in soil and may persist in plant debris or on roots of weeds. Damping-off tends to be most severe under conditions of high soil moisture and compaction. Moderate temperatures, especially when onion crops are grown in succession, favor this disease. In greenhouses, damping-off can be more common when improperly pasteurized soil or previously used seedling trays are used for planting. Water splash can move infested soil from diseased to healthy plants and spread this disease.
Disease management
Control of disease is dependent on minimizing soil moisture: break up compacted soil; plant in well-draining areas or raised beds; treat seeds with appropriate fungicides prior to planting.
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