Black knot on a fruit tree. Photo by Pat Stinson.
By Jennifer Devine
Editor’s note: This article appeared as a post on the Facebook page of Michigan Survival and Homesteading Guide, an informational blog written by the author. An edited version is reprinted here by permission.
Black Cherry Tree
Step outside and see our northwest Michigan landscape in the process of changing from brown to green. Most trees (except pine, now filled with growing pinecones) are leafing out.
But there is one tree that has been leafing out for weeks: the deciduous black cherry tree. Do you see it? Interspersed with all the pine, oak, birch, maple and poplar are skinny-trunked and skinny-limbed trees lined with bright and smooth elongated green leaves. The base of these leaves, if you look closely, come from a red “hair.” You may even see the beginning of a cluster of flowers 5 inches long at the end of leafy twigs in spring, with numerous third-of-an-inch white flowers with five petals that, if pollinated, will bring a harvest of delicious wild black/purple cherries. Chokecherries are similar, however more shrub-like, and the leaves are far more rounded.
Look closer still and you may see what I always called “tree poop.” Yeah, that’s not the scientific name, but I bet you’ve thought it too!
Black knot
Black knot (Dibotryon morbosum or Apiosporina morbosa) is a fungus that affects cherry, apricot, plum and chokecherry trees in North America. Do not confuse this with the very edible chaga, a mushroom which grows on the trunks of birch trees and looks similar. Black knot affects the limbs, rarely the trunk, of fruit trees, encircling the limb and literally suffocating it.
In spring, two winters after initial infection, the fungus produces sexual spores called ascospores. The ascospores mature during the spring of the second season and are forcibly discharged into the air during rainstorms. They are distributed short distances on wind currents and through rain splashing and infecting young saplings and wounded limbs. The anamorph, or sexual stage, produces abundant olive-green fungus spores or “conidia” during the summer on the surfaces of one-year-old knots. If not treated, the next year you will see gnarly black knots.
Is the tree completely covered with black knot? It’s probably best just to get rid of the whole thing, as it is already dead. There’s no coming back.
Is your tree still salvageable? If there are green leaves and other healthy limbs, the answer is YES! All you need to do is grab your pruning shears, a garbage bag and 70% rubbing alcohol or bleach. Dip the shears in the alcohol or bleach to sanitize them, prune the infected limb about 8” below the black knot toward the trunk, and put it in the bag. Careful not to cause too much disturbance or more ascospores will spread. Repeat as needed, sanitizing between cuttings. After trimming, do a heavy sanitize on your tools.
The fungus does not affect our health, so you could use those limbs in your bonfire or burn barrels. Just be careful, again, not to spread the disease. Do not compost them unless you know your compost temperature is 160 degrees or hotter.
Now, sit back and enjoy the beautiful color, the perfume in the air and, later in summer, some sweet wild black cherries.
Get out there and enjoy MI Backyard.
Jennifer Devine is a homesteader with 20 acres of trees. She and her husband have a license to sell black cherry, white oak and white pine. They live off grid and have chickens, ducks and rabbits, a large garden and a lot of woods. She homeschools her two young ones and calls it “an adventure.”
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