Damping Off Disease – Prevention and Treatment

Damping off disease is probably the number one killer of small seedlings. If you grow anything from seed you should be familiar with this problem and know how to prevent it. If your seedlings already have the disease – read on – I’ll show you how to fight it.

What is Damping Off Disease?

Gardeners consider this to be one disease but it is actually many diseases. “Numerous soil-borne fungi belonging to over a dozen of genera” have been reported to cause damping off. Most of these are common in soil. The fungi, Rhizoctonia spp. and Fusarium spp., along with the water mold Pythium spp. are the most common culprits.

Think of damping off as a type of disease and not a specific disease, in the same way that a virus infection is a type of disease that can be caused by many different organisms. Knowing this, it should come as no surprise that there are a range of symptoms for damping off, and a variety of conditions that encourage its spread.

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Most gardeners identify the disease after the seedling makes an appearance above ground, but the disease can strike even before there is any above ground growth. Scientists divide the diseases into two groups: pre-emergent and post-emergent. The former is a larger concern because it affects food crop seeds in the field and can have a dramatic effect on yield. I suspect this also happens to gardeners quite a bit, but we tend to blame seed quality or the weather on poor germination.

The post-emergent version is of most concern to gardeners because it is so much more visible.

Damping off disease affects smaller seedlings. Once they produce true leaves the stem hardens off and the plants are less susceptible to the fungus.

Symptoms of Damping Off Disease

Since damping off is a range of diseases there are also a range of symptoms.

• White/pink/gray cottony fungus may appear at the base of the stem.
• A seedling may look quite healthy except for the fact that it is laying on the ground. When you look closely at the stem near the ground it is darker in color, thin, almost thread-like. The seed leaves still look green and healthy, at least for a while.
• A complete lack of germination. If the root is infected soon after it starts to grow, the shoot can rot underground before you ever see it.
• Rotted roots.

Preventing Damping Off Disease

Prevention is quite simple for gardeners starting seeds indoors but it is much harder to do in the field.

Every winter I see numerous posted pictures showing pots of dead and dying seedlings accompanied by a plea for help. Invariably, those pictures show a very wet soil, indicating that the damping off problem was caused by improper watering. Fungus grow best in wet conditions and overwatering gives it the perfect place to grow.

Here are some ways to reduce the chance of getting damping off.

• Keep the soil drier. Don’t water until the surface of the soil is dry. A one inch seedling already has a root that is two inches deep. The surface does not need to be wet.
• Keep a fan running 24/7. The fan keeps humidity from gathering at soil level and helps dry out the surface of the soil.
• Use fresh seedling mix. Don’t reuse seedling mix to start seeds. It is fine to reuse it for other purposes like repotting larger seedlings, but not for germinating seeds.
• Keep seedlings at the right temperature. A temperature that is too low or too high can weaken the seedling. Pythium is most active in wet, warm soils, while Rhizoctonia is more active in cool, moist soils.
• Clean your grow area, including pots and tools.
• Use seed treated with a fungicide.
• If you germinate under a plastic dome, remove it, at least partially, as soon as seed starts to germinate.

I rarely get damping off and I have been starting seeds indoors for 30+ years. I don’t clean up my work area but I do use fresh media and keep it on the dry side. I also run a fan 24/7. The fan and less watering are the most important ways to control it.

Treatment for Damping Off Disease

You have to act quickly once you notice the problem. Infected seedlings are unlikely to recover and if they are laying on the ground they are definitely goners. You can however prevent the fungal infection from spreading to other seedlings.

The following sections discuss treatment options that are promoted online.

Cinnamon for Damping Off

I have written a complete post on the use of cinnamon for damping off, so I’ll just summarize the key points here. For a more detailed discussion see Cinnamon – Does It Stop Damping Off in Seedlings?

There are many types of cinnamon and the one in your spice cabinet it probably not true cinnamon. For this reason anything that I say about cinnamon may or may not apply to the stuff you buy.

Cinnamon does have anti-fungal properties. Scientists using cinnamon extracts have shown that it is effective against some species of damping off fungi. That sounds promising, but the extracts are usually concentrated alcohol extracts. Alcohol is very good at extracting organic compounds so it concentrates the active ingredients. Many of these studies also use leaves and not the bark which is used to make the spice.

Gardeners on the other hand sprinkle ground bark on the seedlings. At best some active ingredient is extracted with water from the wet soil but that is not nearly as effective as alcohol.

The science is positive but we can’t extrapolate it to the way we treat our seedlings.

There are many anecdotal reports saying that cinnamon stops damping off. I’ll add to that list. I have used it and it always seems to stop the disease. I don’t know if it is the active ingredient, or maybe it just dries out the soil enough to stop the fungi from growing? I have covered very visible mycelium growth with it, and the growth seems to die, but I don’t know what species of fungi I treated.

Bottom line is that we don’t have scientific proof that cinnamon powder works, but a lot of gardeners do report success with it.

Chamomile Tea for Damping Off

This is another common remedy suggested by gardeners. You brew some chamomile tea and use that in a diluted form to treat seedlings.

Chamomile oil does show antifungal properties, but this would normally be extracted using alcohol, or even distillation. An oil extract did reduce damping off fungus on pine seedlings. One study reported the tea had some moderate antifungal properties but another study that looked at aqueous extracts of 22 of plant species found no reduction of damping off fungi for chamomile.

There are numerous anecdotal reports that it works and I tried it once and it seemed to work, but I did not have controls and without them, who knows if it worked. I might have watered less at the same time or turned the fan on high. Anecdotal evidence without controls is of limited value.

What is the proper way to make the tea? Can you use commercial tea bags or do you need to use collected dried blossoms as in this recipe; pour one cup boiling water over one-fourth cup dried chamomile blossoms. There are also two species of chamomile, the German and the Roman. Extracts made by laboratories show different compounds from each one and yet gardening advice never specifies which one to use.

There is no science to support the use of chamomile tea and I doubt there ever will be any because making tea is not an efficient way to extract the active compounds.

Sand on the Surface

Some suggest that placing a sand layer on the potting media will keep the fungi from growing. I found no evidence this works and I have my doubts. The sand would keep the surface of the media wetter, which the fungi want. It doesn’t seem like a good idea to me.

Fungicides Stop Damping Off

There are a number of commercial products, like Captan, that will work, and some can even be sprayed before you see any damage to seedlings. Pretreating vegetable seed with a fungicide is common.

There is a fundamental problem using fungicides. They only work if you apply the right one for the species of fungi you have, and it’s pretty impossible for gardeners to correctly ID the species causing the problem. So a fungicide may not work in your case because you picked the wrong one.

Biologicals Stop Damping Off

A number of biological organisms have been isolated and formulated into easy to apply products. These include “Bacillus subtillus (Companion), Streptomyces lydicus (Actinovate), Streptomyces griseoviridis (Mycostop), Trichoderma harzianum (PlantShield, Rootshield), and Trichoderma virens (SoilGard)”. These products are generally watered in before you see a problem. It is important for the applied organism to grow in the potting media before the damping off fungus takes hold.

One such species, Streptomyces sp. Di-944, was isolated from the rhizosphere of field-grown tomatoes where it naturally suppressed damping-off caused by Rhizoctonia solani.