Damping off disease can be one of the most frustrating problems when starting seeds. Luckily there are things you can do to prevent large losses.
What Is Damping Off Disease?
Damping off is a common fungal disease found in young seedlings. It’s probably one of the most frustrating problems that can occur when starting seeds, especially indoors.
By the time you realize a seedling has been infected, it’s too late. Even worse, if one seedling in your tray is infected there are probably many more. It’s not uncommon to have to throw away an entire tray of seedlings.
The good news is only very young seedlings are affected. If you can use these tips to safely protect your seedlings to the point where they get some true leaves you are most likely safe.
Identification
Technically there are 2 types of damping off. Pre-emergence and Post-emergence.
Pre-emergence damping off occurs when the sprouting seed decays before breaking the soil surface. This type of damping off isn’t as commonly identified since seedlings aren’t visible. People usually chalk up the lack of growth to poor germination.
Post-emergence damping off is much easier to identify. You will likely see a seedling that has just emerged from the soil with healthy looking leaves but it is completely flopped over.
After more careful observation you’ll see that the seedlings stem, especially down low near the soil line, is extremely thin, or thread like.
Causes
There are 4 main pathogens that can cause damping off: Pythium, Phytophthora, Rhizoctonia, and Fusarium spp. These pathogens can get introduced into your seed starting setup in a number of ways:
* Contamination from previous years seed starting supplies. This is one of the most common causes since gardeners try and save money by sterilizing old trays, cell packs, and plastic domes.
* Contamination of garden tools including shovels, gloves, watering cans, and even dirty hands.
* Use of a non sterile potting mix that contains the pathogens that cause damping off.
Even if you’re convinced all your material is sterilized, including your potting mix, it is still likely that some or all of the pathogens that cause damping off are still present.
The key is to be aware of, and avoid, the growing conditions that make these pathogens thrive. Generally they thrive under conditions that slow plant growth:
* Low potting mix (or soil) temperatures
* Over watering and top watering
* Low light intensity or not enough hours of light
* Too much salt which can come from over fertilizing
Treatment
There isn’t much you can do to treat an infected seedling. You can however reduce loss by quickly removing six pack cells in which even one seedling has been infected.
If multiple seedlings are showing signs of the fungus then remove the whole seed tray.
If you’re not ready to part with wasting an entire tray of seeds then consider having a secondary setup that is completely separate from your healthy seedlings. You might get lucky and have some healthy seedlings pop up.
Since damping off disease can be near impossible to treat, prevention is definitely best.
Preventing Damping Off Disease
* Buy new seed starting supplies instead of sterilizing last years supplies. Seed starting materials are relatively inexpensive.
Sterilizing all your cell packs, trays, and domes takes a lot of time and it’s still likely you will have some contamination. If you insist on sterilizing, consider using 10% bleach soaked in water for half an hour.
* Use new potting mix. Don’t use mixes that are old or have been left open since last season. Purchase sterile mixes or take an extra step and sterilize your own potting mix.
* Use a quality heating mat under seed trays. Ideal soil temps for seed germination is 70-75 degrees. If it’s the middle of winter and you are starting seeds in your basement then heat mats are especially useful. This will help speed germination and get your seedlings established before damping off has time to take hold.
* Keep a fan running at low speed, at all times once you have removed humidity domes. This will increase air circulation and help dry out the top layer of your seedlings where damping off occurs. This also helps prepare seedlings for wind conditions they will be facing while hardening off.
* Monitor your watering. Once you remove humidity domes, after your seeds have germinated, back off on watering. Keep a small amount of water in the bottom of your seed tray.
Do not overfill seed trays with water or water seedlings overhead. At this point you want the surface of the potting mix to be moist but not wet.
* Wait until your seedlings have true leaves before using a good liquid fertilizer.
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