Damping-off is a common problem when greenhouse or field seedlings are grown in wet or infected soils. Damping-off is caused by various soilborne pathogens such as Pythium, Phytophthora, Rhizoctonia and Fusarium species.
Infected plants typically fail to emerge from seed, or seedlings collapse and die soon after germination. Stems will turn black and shrivel at the soil line. Pythium spp. can also cause root dieback in carrots later in the season.
Damping-off typically occurs during times of cool and wet weather. Soilborne pathogens thrive in moist soils, ideally around 6.8 pH. Pythium overwinters in the soil as survival structures called oospores, which then become active as the soil temperature warms. Under saturated conditions, Pythium forms swimming zoospores, which cause infection.
- Maintain uniform soil moisture at seed depth. Prevent over or under watering. Pythium requires free water to spread, and allowing soil to dry between waterings will help prevent infection. Avoid planting seeds too deep.