Q: As I inspected my forsythia recently, I saw several odd-looking knots on stems that had few flowers. Can you tell me what this is?
A: Crown gall is caused by a bacteria. It induces the host plant to produce hormones that cause abnormally rapid cell division and enlargement of stem tissue. Galls range in size from a fraction of an inch to several inches in diameter. The disease affects forsythia, euonymus, willow, oak and several other plants. Galls interfere with water and nutrient transport and can result in unthrifty plants or death; however, in many cases the damage is mainly cosmetic.
The best treatment on forsythia is to prune out the galls ( make your cut 3 – 4 inches below the gall) and dip your pruner in a 1:10 bleach:water solution between cuts so you don’t spread the disease.