Forsythia – Stem Gall Disease

Q: I transplanted a large forsythia last spring and managed to get it through the summer drought. It flourished and I began to neglect it – at least I wasn’t checking it hourly like a new mother. Now I find it has clusters of “knots” throughout approximately one third of the bush and it appears that that section is sick and dying. Is this a disease? Should I remove the diseased parts of the bush?

A: Your forsythia has a disease called forsythia stem gall on its stems. Galls like this are common among trees and shrubs. I once saw a tree in Hawaii that had suffered from the disease for many years. The swollen and gnarled trunk gave it the appearance of a huge owl getting ready to hoot at hikers as they passed by.

There are no curative sprays for the galls so the best treatment is to prune out the affected branches. Make your cuts at least six inches below the knots. It would also be a good idea to disinfect your pruner with a 1:10 solution of bleach and water between cuts.

Forsythia stem gall