Problem type: Disease
Name of problem: Damping-off
Plant name(s): Seeds and seedlings of all plant types
Symptoms / Characteristics:
Damping-off is essentially the in situ rotting of seeds and seedlings. It is an extremely common disease that can occur both before and after emergence. Failure to emerge through the soil surface indicates that the seed or germinant may be infected with damping-off disease. The seeds and germinants must be retrieved and examined for evidence of rotting in order to confirm the disease. In post-emergence damping-off, above-ground symptoms are visible. Girdling of the stem occurs at the soil line. As a result, the stem weakens and eventually the entire shoot collapses. Plant death does not occur in every case. Healthy seedlings may avoid or at least withstand infection, suffering only minor setbacks in growth and development. Seedlings typically become resistant shortly after they have emerged, although woody plant seedlings often remain susceptible until the woody stem has formed (4-6 weeks).
Damping-off is caused by several species of fungi, including Pythium, Rhizoctonia, and Phytophthora. These pathogens exist in both field and greenhouse soils. They may also be introduced with the seed or in contaminated water. Using dirty, contaminated tools often facilitates pathogen transfer. Prolonged periods of high moisture and cool temperatures favor the development of the disease. Such conditions delay germination and emergence, extending the time period in which the seeds/seedlings are susceptible to attack. High moisture, however, is a key element. Soil type also plays a critical role. Heavy soils tend to hold more moisture and harbor more damping-off fungi. For Pythium and Phytophthora, water is necessary for infection.
Control / Preventions:
Before planting, use a fungicidal seed and/or soil treatment to protect seeds and young seedlings from soil-borne diseases during the early stages of growth and development. Use sterilized soil/growing media in seed trays and seedbeds in order to reduce potential sources for the disease. Also, use only clean, disinfected containers and tools. Keep potting areas clean and sanitized. Eliminate weakened and diseased seedlings prior to transplanting. These plants may already be infected with a damping-off pathogen and advancing them to a clean field or bed would likely lead to future infestations. The most effective control is to avoid conditions that favor the development of the damping-off disease. This involves effective water management and a balanced fertilizer program. Applying too much nitrogen fertilizer may render the young seedlings especially susceptible to damping-off. Avoid watering seedlings late in the day; early morning is the best time to water. Avoid planting in low-lying areas with heavy or highly compacted soil, as poorly drained soils typically harbor more damping-off pathogens. Ensure adequate spacing between seedlings to promote air circulation and reduce humidity. Once disease symptoms become apparent, a fungicidal soil drench may be used to prevent further infections. Severely infected plants are generally untreatable.