Cottage Q&A
QUESTION
Last summer, I spotted this bush at the cottage. Its leaves have sprouted
all sorts of growths, although otherwise, it seems healthy. What's going on?
ANSWER
Your viburnum, sporting those club-like appendages from its leaves, has a classic case of spindle gall. But relax, it's harmless, according to Alan Watson, director of The Arboretum at the University of Guelph, even if it looks ugly. "Actually, some people think it's rather pretty," he muses.
Galls are created by a variety of insects or mites, as well as fungi, bacteria, and other organisms; in this case, mites that feed and breed on leaves, causing the plant tissue to distort and form a hollow structure that expands as the leaves grow. The female mites lay numerous eggs inside and feed on the softer new growth of the gall. When the young mature, they exit the gall to start the cycle over again on new leaves. "Different species of mites go after different plants," Watson says. Some prefer viburnum, some birch, while others have a taste for maples. Spindle gall grows around the Eriophyid mites, providing a home for generations of viburnum connoisseurs. These mites are microscopic beasties a quarter of a millimetre long that hitch a ride on birds, other insects, and even the wind. Now that you have noticed one bush growing spindle gall, you'll probably see others coming down with a similar case of plant acne. It's pretty hard to do battle with an unseen enemy; however, you could try removing infested leaves, which may put a dent in the mite population. In severe cases, apply a dormant oil spray in early spring to the trunk or branches, where the females overwinter. But, Watson warns, it is difficult to get the timing right. Since they've now arrived at your cottage, chances are the mites and galls will take up permanent residence.
* Published in the March 2006 issue of Cottage Life
