Black Knot Disease on Schubert and other chokecherry trees

Roots, Shoots and Suckers

Keith Anderson

You’ve all seen it. You’ve all exclaimed, “Woah! That looks like …t! “So what is it? How did it get there?

The good thing about a tree disease is that a tree disease does not affect all types of trees. Certain diseases affect certain trees and do not move onto other tree species or animals. This is called “host specific” and is the only reason after all these years of working with trees I remain Dutch Elm Disease free. My symptoms are the result of something totally different, that thankfully, trees will not get.

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Black Knot Disease affects chokecherry trees including the well-liked, admired, purple-leaved Schubert chokecherry. It is rampant across the prairies both in the wild and in suburban landscapes.

The disease looks like a black mass of burnt rope (this is the polite way to describe poop on a schtick) and sometimes has grey or maroon colouration in the growth. It is usually found on branches, but can also be found on the trunk. Early in spring, a new infection will look like a linear brown swelling on a twig or branch.

This is a fungus that is spread by fungal spores. These spores are carried by birds, insects, wind and rain splash.

What to do about this nasty looking blemish on your landscape? First of all, just be happy that you don’t have any of these growing on your own limbs. Secondly, you have to remove this infection. You must make the cut approximately 12 inches below the infection site (towards the main trunk) preferably at a branch junction.

The best time to do this is when the leaves are off because the infection sites are very visible and the disease is not active.

If you do remove infected tree parts during the growing season there are two things to remember. It is one of the few instances when I recommend painting the wound with tree tar. I believe it can help prevent a re-infection at the fresh cut. The second thing to remember is that if you are pruning diseased wood then you should dip your shears or spray down your saw with a bleach solution or methyl hydrate to disinfect your tools so that you reduce the chance of spreading the disease to other parts of the tree.

If the disease is in the trunk then one pruning cut should suffice if it is made very close to the ground (remove the tree).

Do not save this wood in your woodpile. The fungus stays active even when stored. Small, infected limbs should be sealed up in a plastic bag and disposed of. Larger limbs or tree trunks should, at the very least, be disposed of in the burn pile at the waste management facility formerly known as “the dump.”

My friend Barry from Battleford calls these blemishes monkey turds. If you see them you will know why he calls them that. He has been trying to keep his Schuberts turd-free for several years. Barry is one of those neighbours everyone loves to have. If he sees the monkey has paid a visit to your landscape, he will probably knock on your door and ask to remove the hideous growth from your tree in an effort to maintain turd-free status in his own yard. Everyone must do their part to keep their neighbourhood free of turds.

Black Knot Disease affects: chokecherry, Schubert chokecherry, mayday and plum trees.

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