Safeguard Your Seedlings from Damping-Off

Damping-off is the rotting of seeds in the soil and the collapse of newly emerged seedlings. Damping-off causes root necrosis (browning), rotting, and sloughing– a condition where the outer root tissue separates from the inner tissue. It is categorized into two types: pre- and post-emergence damping-off. Pre-emergence damping-off destroys the radicle and hypocotyl before the seedling emerges from the soil surface. Post-emergence damping-off occurs after emergence and is characterized by stem rot at or just below the soil line. Affected seedlings may discolor, wilt, collapse, and die. Damping-off is caused by several different fungi and water molds (Oomycetes), including Rhizoctonia spp., Fusarium spp., Pythium spp., and Phytophthora spp. These pathogens may act independently or co-occur to cause damping-off.

Whether you are starting seeds indoors or growing crops in the field, damping-off can occur in both environments. Damping-off is most severe under conditions of excessive soil moisture and high humidity. The disease often begins in localized areas with poorly drained soils and overcrowded seed beds, then spreads over time. Under moist conditions, diagnostic signs may be visible on the affected tissue. Rhizoctonia produce white to tan-brown mycelium, Fusarium produce signs of white to orange-pink fungal growth, and Pythium and Phytophthora produce white, cottony mycelium. Certain taxa within these genera cause additional diseases beyond the damping-off described here and may require additional management strategies.

Rhizoctonia, Fusarium, Pythium, and Phytophthora are soilborne pathogens that can spread on infected seeds and transplants, contaminated soil, irrigation water, equipment, tools, pots, and stakes. People may also inadvertently spread these pathogens when contaminated soil clings to their shoes or when they handle diseased plants before healthy ones. Many soilborne pathogens can survive on weeds or crop debris in the soil. They may also produce survival structures that enable them to persist in the soil in the absence of a host plant.

Implementing an integrated approach for disease management is essential for preventing damping-off and minimizing losses:

• Start with pathogen-free seeds and healthy transplants.
• Grow disease-resistant cultivars or graft onto resistant rootstocks.
• Remove and discard plants showing symptoms of damping-off.
• Clean and sanitize tools and equipment before reusing.
• Use sterile growing medium and disinfected pots, trays, and flats.
• Frequently wash hands and clean and disinfect shoes using footbaths between production areas.
• Avoid overwatering and planting in poorly drained field soils, as saturated conditions can favor damping-off pathogens.
• Avoid overseeding and properly space plants to improve air circulation and reduce humidity.
• Manage weeds, which can harbor pathogens.
• Remove or plow under crop debris following harvest.
• Rotate away from susceptible crops for as long as possible.
• When warranted, use fungicide as a seed treatment or before, at, or after planting, and always follow product label instructions.

For additional information on damping-off management, consult the Penn State Extension website. Commercial growers should refer to their specific production guides, such as the Mid-Atlantic Commercial Vegetable Production Recommendations or the Penn State Agronomy Guide, which offer fungicide recommendations tailored to individual crops. Fungicides vary in their use and efficacy against the different damping-off pathogens. Therefore, it is important to accurately identify the pathogen causing damping-off. Pennsylvania residents have the wonderful opportunity to submit plant samples for FREE to the Penn State Plant Disease Clinic for evaluation of damping-off and other diseases. When submitting samples for suspected damping-off and other root diseases, be sure to include roots in your sample, approximately one cup if possible. Additionally, companies like Agdia, Inc., offer plant diagnostic testing services and Immunostrip® tests for some damping-off pathogens, such as Rhizoctonia solani and Phytophthora spp., which can be done on-site by growers. Informed diagnosis and proactive disease management are the foundation of control.