Black knot?

Asked March 24, 2016, 4:44 PM EDT

Client stopped in with a sample growing in her tree. The branches seem to get black fungus knobs partially up the center of the branches. This has been happening the last 2 to 3 years. Client has been trimming them out. Please diagnose and make recommendations

Lake County South Dakota

1 Response

This is the fungal disease 'Black Knot'. This is a common disease of chokecherry, particularly its many cultivars, and the Mayday tree (a European cherry). There is no cure for the disease. You can prune out every knot and they will come back as the first year infections are very difficult to detect, only a slight swelling on the shoot, and these need to be pruned out as well. There is a wide variation in resistance and trees that have the disease will always have the disease so removal is the best option.