Damping off disease is one of the most destructive diseases affecting seedlings and transplants. It can cause significant losses in farms, nurseries, greenhouses, and home gardens by killing seedlings before or soon after they emerge. Understanding the causes, symptoms, and management of damping off is key to preventing and controlling this common disease.
What Causes Damping Off Disease?
Damping off is caused by several fungi including Pythium, Phytophthora, Rhizoctonia, and Fusarium species. These soil-borne pathogens infect the seeds, seedlings or transplants at the soil line causing the stems to shrink and rot. Damping off fungi thrive in wet, poorly drained soils with high moisture levels. Cool soil temperatures and high humidity also favor disease development.
The fungi produce motile zoospores that can swim in water films around soil particles. When seeds germinate or seedlings emerge, the zoospores infect the succulent stem tissues at the soil line. The fungi grow into the stem, disrupting water and nutrient transport in the plant. This causes the seedling to collapse and die which is described as “damping off”.
Key factors leading to damping off disease include:
- Excess moisture in the soil from overwatering, poor drainage or heavy rains
- Cool soil temperatures between 50-60°F
- High relative humidity above 85%
- Overcrowded seedlings allowing fungi to spread
- Poor sanitation allowing inoculum to persist in soils
The main damping off fungal pathogens include:
- Pythium spp.
- Phytophthora spp.
- Rhizoctonia solani
- Fusarium oxysporum
- Thielaviopsis basicola
Pythium and Phytophthora species are called water molds and prefer wet, poorly drained soils. Rhizoctonia and Fusarium favor slightly drier conditions. Thielaviopsis basicola causes black root rot in seedlings. Most damping off fungi produce resting structures that allow them to survive in soil or plant debris for many years.
Symptoms of Damping Off Disease
Damping off can occur before or after seedlings emerge from the soil. The symptoms include:
Pre-emergence Damping Off
- Failure of seeds to germinate and emerge
- Decay of seed before germination
- Rotting of seedlings before they break through soil surface
Post-emergence Damping Off
- Water-soaked lesions on stem at soil line
- Stem collapse and shriveling near soil line
- Dead, collapsed seedlings laying on the ground
- Fungal growth visible on affected stems
- Rapid death of seedlings in patches
Post-emergence damping off can occur quickly, sometimes killing seedlings overnight. Lower leaves initially appear wilted, and the weakened stems fall over. The infected area of the stem near the soil will show water-soaked, soft, mushy tissues. A lesion develops as the fungi invade the stem vascular tissues cutting off water supply. The seedling eventually collapses and dies.
Factors that increase damping off severity:
- Dense spacing of seeds/transplants
- Cool, wet conditions
- Working soils when wet
- Insufficient light
- Nutrient deficiencies
- Transplant shock
- Root damage from transplanting
Plants most susceptible to damping off disease:
- Beans, peas, soybeans
- Cucumbers, melons, squash
- Onions, cabbage, broccoli
- Lettuce, spinach, beets
- Flowers like marigolds, zinnias
- Ornamentals like roses and bedding plants
- Tree seedlings like pines and oaks
Young succulent seedlings and transplants are at greatest risk before their stems lignify and roots establish. Damping off rarely affects mature plants. Some varieties of crops are more tolerant while others are quite susceptible to the disease.
How to Prevent Damping Off of Seedlings
Prevention is the key to controlling damping off disease in plants. Good cultural practices and sanitation will reduce fungal inoculum and create unfavorable conditions for infection.
Provide Proper Soil Drainage
Excess moisture promotes damping off fungi. Ensure seeds and transplants are in well-drained soils or planting mixes. Raised beds can improve drainage. Avoid overwatering and wetting foliage. Allow soil to partially dry between irrigations.
Use Sterilized Soilless Mixes
Use a sterile, soilless growing medium when starting seeds or transplanting. Commercial potting mixes are pasteurized to kill damping off fungi and other pathogens. Make your own mix using compost, vermiculite and perlite.
Follow Good Sanitation Practices
Disinfect pots, trays, propagation tools and greenhouse surfaces. Remove and destroy infected seedlings immediately to limit spread. Rotate seedlings in new ground annually. Allow 2-3 years before replanting in previously affected areas.
Give Seedlings Space and Light
Avoid overcrowding and ensure ample air circulation around seedlings. Thin seedlings to recommended spacing. Provide 14-16 hours of light daily for rapid, healthy growth.
Use Fungicide Seed Treatments
Treat seeds with fungicidal products containing captan, thiram or metalaxyl to kill damping off fungi. Biological controls like Trichoderma species can also protect seedlings.
Use Bottom Heat for Warmth
Maintain soil temperatures at 65-75°F to discourage fungal pathogens. Bottom heat, heating cables or heating mats can gently warm the root zone.
Allow Soil to Dry Between Waterings
Let the soil dry down slightly before watering to avoid saturated conditions. Water early in the day so foliage dries quickly. Drip irrigation is ideal for delivering water right to the roots while keeping foliage dry.
Improve Soil Nutrition
Healthy, vigorous seedlings are less susceptible to disease. Test soils and amend appropriately to ensure balanced fertility.
Choose Resistant Varieties
Select vegetable varieties labeled as resistant (VR) to races of fungal pathogens like Fusarium oxysporum. Some varieties tolerate damping off better than others.
How to Treat Damping off in Seedlings
If damping off occurs, prompt action is needed to contain the disease and protect remaining seedlings.
- Immediately remove and destroy badly infected, dying seedlings. Do not compost.
- Improve air circulation and light exposure between plants.
- Apply fungicide drenches to soil such as mefenoxam for control of Pythium and Phytophthora. Follow label directions carefully.
- Drench soil with beneficial fungal products containing Trichoderma species to parasitize disease fungi.
- Allow soil to dry between waterings and avoid wetting foliage.
- Space out seedlings further if possible and replant if needed.
- Treat remaining plants with OMRI-listed biofungicides based on Bacillus subtilis to suppress damping off pathogens.
With vigilance and prompt action, damping off damage can be minimized. But prevention is most effective through proper cultural practices to create soil conditions unfavorable to the disease. Carefully follow seed planting guidelines, ensure good drainage, provide adequate space and avoid overwatering. Inspect seedlings daily and quickly treat or remove infected plants. Using clean techniques when starting seedlings or transplanting can help avoid introducing damping off fungi in the first place.
Frequently Asked Questions About Damping Off
What is damping off disease?
Damping off disease is caused by soil-borne fungi that infect seedlings at the soil line leading to rotting and collapse of stems. Pre-emergence and post-emergence damping off can kill seedlings rapidly.
What causes damping off fungi?
Excess moisture and cool temperatures favor damping off pathogens including Pythium, Phytophthora, Rhizoctonia, and Fusarium species. They thrive in wet soils and infect succulent plant tissues.
How do you fix damping off?
Improve drainage, avoid overcrowding, remove infected plants promptly, apply fungicides, introduce beneficial fungi, and follow good sanitation practices. Reduce moisture and use bottom heat to warm roots.
Can damping off be cured?
There is no cure once seedlings are infected. Prompt removal of diseased plants and preventative fungicide applications can help stop spread and protect healthy seedlings.
What is the best treatment for damping off?
Prevention is key! Sterilize soils, use clean containers and tools, avoid excess moisture, allow proper spacing and airflow, and use fungicidal seed treatments. Maintain optimal temperatures and treat immediately at first disease signs.
What are signs of damping off?
Signs include failure to emerge, collapsed seedlings, water-soaked stems at soil line, shriveling lower stems, lesions, rot, fungal growth on affected areas leading to rapid plant death.
Can damping off spread?
Yes, damping off fungi can spread readily in moist soils via swimming zoospores. Overcrowding worsens spread from plant to plant. Remove and destroy infected plants quickly.
Is damping off fatal?
Yes, damping off is usually fatal to infected seedlings which collapse and die rapidly. Older plants can better withstand infection without dying but may be stunted.
How do you disinfect soil for damping off?
Heat sterilization, solarization, or fumigation can disinfect soil. Or drench soil with fungicides or beneficial microbiologicals prior to planting. Potting mixes can be safely reused after steam or chemical treatment to kill fungi.
Can damping off return?
Yes, damping off fungi produce persistent spores that can survive for many years in soil or plant debris. Rotating plantings and avoiding repetitive plant families helps reduce inoculum.
Conclusion
Damping off disease requires close monitoring, prompt action, and excellent prevention measures to avoid significant losses of seedlings or transplants. Carefully regulate soil moisture and temperature conditions to prevent fungal pathogens from thriving. Follow good sanitation practices and treat at the first signs of infection. With proper management, damping off can be controlled to ensure healthy, vigorous seedlings. The keys are avoiding excess moisture, lowering density, and creating an environment unfavorable to fungal pathogens in the soil and growing medium. A combination of cultural techniques and targeted fungicidal treatments will provide the best protection against damping off disease.