Black knot on trees

At this time of year, when the leaves have gone, you may notice black swellings on some of the branches of your Schubert chokecherry, Mayday or Pincherry trees. This is most likely black knot.

The fungus that causes this disease mainly affects the new growth on the tree, cutting off nutrients and stunting the growth of the tree. It becomes worse every growing season and may eventually kill the tree. The fungus is spread in the spring, onto the new shoots by rain, wind, and insects. In order to control its spread onto other branches or neighboring trees, the infected area needs to be pruned out before bud break in the spring. Cut 10 cm down from the infected area, and burn or bury the infected branch. Do not compost or mulch. Disinfect your pruning tools with a 10% bleach solution after every cut.