Damping off is a term commonly used for the sudden death of young seedlings. This occurs when pathogens cause new shoots to decay and die not long after germination. It’s a common cause of failed seeds or seedlings. Some seeds even rot and die before germinating.
Learning how to prevent the conditions of damping off will help keep your seedlings happy and healthy.
Damping Off Disease
Damping off (also written as damping-off) occurs in many types of soil and in various climates. It affects both flowers and vegetables. The amount of damage to seedlings depends on the particular fungus, soil moisture, and temperature. Often, germinating seeds are killed by fungus prior to emerging from the ground.
Several soil-borne fungi can be responsible for damping off, including Rhizoctonia solani, Botrytis, Sclerotinia, Sclerotium, Fusarium spp, Pythium spp, and Phytophthora spp. Though many pathogens can lead to damping off, the results are always basically the same.
Older, more established plants are seldom affected. However, portions of the roots and stems can still be attacked, resulting in poor growth and reduced yields.
What Does Damping Off Look Like?
If you've experienced failed seeds or seedlings, there is a good chance you lost them to damping off. It’s a common occurrence that causes seeds and seedlings to rot before they can fully develop.
So, what does damping off look like? This often depends on the particular fungus, but there are some common signs of damping off in seedlings. Here are some signs and symptoms:
- The seedlings never emerge from the soil.
- The cotyledons (first leaves to appear) are water soaked.
- The cotyledons may be gray or brown.
- The stems are water soaked and very thin.
- Rotting often begins on the stem at the soil line, causing the seedling to fall over.
- Early leaves wilt and turn gray or brown.
- The roots are very small, stunted, or non-existent.
- Any roots that do form have sunken and gray-brown spots.
- There may be some white, fluffy growth on the seedlings.
Conditions of Damping Off
What causes damping off? The phenomenon is caused by fungi in contaminated soil. If the pathogens are introduced to a seed tray, they can affect all seedlings. The wetter the soil, the more likely plants are to be affected. Some of the fungi that cause damping off can swim through water to get to other tray cells and infect more plants.
Unfortunately, the conditions required for seed germination also create favorable environments for the growth of fungus, as both seeds and roots must be kept moist and warm. The conditions of damping off vary depending on the fungus.
Normally cool, wet soils favor development of the disease. For instance, the fungal disease Pythium root rot occurs with cooler temperatures in poorly drained soils. The lower portion of the stem may become slimy and black. Rhizoctonia root rot occurs with moderate moisture levels in warm to hot temperatures. Infected plants often have sunken lesions on the stem at or below the soil line.
The fungi that cause damping off are found naturally in garden soil, but seedlings are not always able to fight off an infection. This is why it is so important to take care when starting seeds to use uncontaminated soil and to keep everything as clean as possible.
How to Prevent Damping off Disease
Seeds and seedlings are vulnerable to fungi and other pathogens. Once a plant has mature leaves and has developed strong roots, it is better able to fight off the natural pathogens in the soil. You have a critical period of time between planting seeds and mature plants during which you can take steps to prevent damping off.
Sanitize
Keep your tools, trays, pots, and working areas very clean to prevent fungi from getting into the seed tray. Avoid working on a wood bench if you can. Other materials are easier to clean. Use a 10% bleach solution to clean and sterilize everything before you begin sowing seeds. Be sure to rinse the bleach thoroughly. If you can, use new seed trays every year.
Purchase a high-quality, sterile potting mix for starting seeds. Don’t let it come into contact with other soils, especially areas outside in your garden. Store unused sterile mix in a sealed container.
Keep Seeds Warm and Not Too Moist
Cold, wet soil promotes damping off in seeds and seedlings. Use a grow lamp that provides some warmth or a heating pad set to 70 to 75 F (21-24 C) under the seed trays. Developing seedlings need 12 to 16 hours of light, so a window is not adequate. Use a grow light for the best conditions.
In terms of moisture, never plant seeds into soil that is wet and soggy. They should thrive in moist conditions, but wet soil and high humidity contribute to fungal infections. Thin seedlings as they grow for good air circulation.
Use Fungicide to Prevent Damping Off
Fungicides may be applied as a soil drench after planting, incorporated into the soil as a dust before planting, or sprayed in mist form on all seedlings. Once transplanted, only those seedlings known to be especially sensitive to damping off need to be misted with fungicide daily until the first or second seed leaves have emerged.
Another option may include seed treatment. Damping off can be reduced by planting fungicide-treated seed directly into the garden.
Starting Seeds Outside
Starting seeds indoors gives you better control over growing conditions. This makes it easier to prevent damping off. If this isn’t an option, you can take a few steps to reduce the risk of damping off in seeds sown directly in beds:
- Avoid starting seeds before the soil has warmed adequately. Check the appropriate soil temperature for whatever type of plant you’re growing.
- Prepare the soil. Damping off is more common in compacted soil.
- Use raised beds, if possible, for better drainage.
- Use clean, warm water to keep the soil moist.
- If using a hose, don’t let the head rest in the soil or on the ground when not in use.
- Don’t use fertilizer until there are several true leaves on the plants.
- It’s always best to start seeds inside if you can. The more control you have over growing conditions, the less likely you are to experience frustrating damping off and loss of seedlings.
Now that you know the answers to the questions "what is damping off" and "what does damping off look like," you can successfully keep it from happening to your seedlings. With a little TLC seed treatment, damping off will be a thing of the past.