Hello all, I've recently moved into a new place and there is a shelter belt in the yard (we are in Saskatchewan) The row of choke cherries is riddled with black knot. I pruned the first bush, but I have some questions that I would like to get answers for before I do the whole row (and potentially cause more harm than good!) 1. Should I prune now, or wait until fall when the plant is dormant? 2. I am trying to cut the branch so I get rid of all the rot, however there are occasions when I cut the branch right back to the crotch (I believe this is the correct term!) but the cut shows that there is still rot inside. Is it best to cut the healthy-looking main branch that the diseased one was attached to, to make sure there is no trace of rot remaining, even if I would cut off quite a large chunk of the bush in doing so? 3. Where is the best place to cut any branch? a) as close as you can to the rot, without having any trace remaining, even if there is no offshoot branch near the cut b) just above the nearest offshoot on the branch c) the crotch where it meets the main branch 4. Should I sterilize the loppers between each bush, even though they all have black knot? Really hope someone out there can help me - I want to do the best job I can! Thank you!
Hello, Black Knot is a common fungal disease of many Prunus trees and shrubs. I am writing this almost two months after your post so you may have already found the answers to your questions, here are mine anyway. 1. Black Knot cankers can be safely removed from the shrub or tree at any time of the year. Spores are produced on the surface of the cankers in late winter/early spring just in time to infect new shoot growth. The cankers should be removed from the plant and destroyed prior to this stage of growth. If you drop the cankers on the ground they will continue to produce spores and that will reinfect your plant. 2. This disease does usually extend several inches beyond the canker inside the branch and all of the infected area needs to be removed or the canker will grow back. The infection in the branch will look like a dark shadow. Remove at 4" - 6 " beyond the canker or more if required. 3. the best location to cut the branch is usually b. just above the next off shoot branch that is clear of infection. 4. This disease is not likely to be spread on pruning equipment. I do not sterilize my pruning equipment when removing these cankers.
