Fungal disease— not tiny aliens — to blame for seedling crop circles
The first time I saw crop circles was when I was a kid. They weren’t the gigantic rings that one might find in some remote cornfield. Instead, they were small circles that were growing in seedling flats in our living room.
Yes, I did say living room. When my mom and dad began their horticulture business, they didn’t have a proper seedstarting greenhouse, so dad just jerry-rigged the living room to accommodate the seedlings. The crop rings would often show up in the seedling flats, leaving a lot of dead plants in their wake.
I always thought these crop circles occurred when the seedlings were too dry, but dad explained that a lack of water wasn’t the problem. Rather, an insidious disease called damping-off was the real culprit.
A BIT OF SCIENCE
Damping-off is not a single plant disease, but rather a group of about three different fungal diseases lumped into one category. Since the affected seedlings look damp and mushy before being “offed” by the fungi, the name really is apropos.
Damping-off is not a rare plant disease. The fungi that cause it are ubiquitous in garden soils, and are even quite common in some seedling mixtures that contain no soil at all. Young seedlings are particularly prone to attack because they have soft shoots and roots that provide little resistance to the attacking fungi.
The reason that damping-off manifests itself as a crop circle is that, in the soil, the fungi often grow from a single, tiny point of infection before quickly radiating through the mixture in all directions, gobbling up seedlings in their paths. The pattern is somewhat analogous to the concentric waves a pebble leaves when it’s thrown into a pond.
WHAT YOU SHOULD DO
The first thing to do to avoid damping-off is to eliminate the use of garden soil in seedling flats. I admit that when we first started growing seedlings we always blended some garden soil into our mixture. It was always pasteurized (heated) to kill the damping-off fungi, which worked reasonably well, but certainly wasn’t perfect. We soon found that eliminating garden soil entirely was a far better strategy. Still, even soilless mixtures can harbour damping-off disease.
One major leap forward in the battle against soil-borne diseases is the advent of soil probiotics, a group of beneficial bacteria — also known as soil activators — that combat damping-off. The mode of action of these probiotic bacteria is multi-faceted.
First, they essentially leave the damping-off fungi homeless by quickly occupying the physical space where the fungi would normally reside. Second, the bacteria steal essential nutrients that are critical for fungal growth. Finally, the bacteria secrete antifungal compounds called iturins. This three-pronged attack is a simple, natural, and beautifully effective way of controlling damping-off.
But don’t forget that probiotic organisms always work best as team players against plant diseases. The winning formula is an excellent growing environment that includes grow lights, water, nutrients, warmth, and high quality root mixtures coupled with probiotic bacteria.
So dad solved the mystery of the crop circles for me long ago; no miniature aliens could take any credit. But to this day, one mystery still remains. How did dad ever convince mom to agree to sacrifice her living room for seedlings? That is a true mystery.