Oak rough bulletgall
Impudence; audacity—gall! My intellectual self tells me that the gall I’ve been dealing with this week is of a different nature, but there are certain times of the year when I’m painfully sure that homonyms are no accident.
I guess I should start by saying that September is the month when the top of my desk takes on a decidedly camouflage look—woodsy, if you prefer…diseased and dying, if you’re into accuracy. Diagnosing customers’ plant problems is nothing new for me, but this week’s batch of samples has left my desk somewhat buried in a sea of gall-covered branches. Still, it’s a nice change from the rotting apples that competed for my workspace last week.
Galls, or bullets, as they are also referred to, can range from small bumps to bizarre-looking, marble-sized growths and are usually found on the leaves and small branches of willows, roses and oaks. And just what is responsible for causing these growths to suddenly show up on trees and shrubs? Gall wasps—600 species of them, to be exact.
Oak rough bulletgall
Home sweet home
If you’ve never noticed gall wasps around your plants, it might be because you didn’t realize what you were looking at. Gall wasps look nothing like the steak-and-burger-eating wasps that buzz our decks during the summer; they look more like tiny, inconspicuous houseflies. But unlike houseflies, gall wasps prefer to build their homes in leaf tissue. And that’s exactly what a gall is—a tiny, one-bedroom home for developing gall wasp larvae. How does a wasp build a home in a leaf? Well, it secretes chemicals that mimic plant growth hormones, of course. These chemical mimics cause the plant tissue to enlarge, thereby creating a protective enclosure in which the immature wasps can grow and mature.
One gall wasp that seems to be a particular problem this year is the oak rough bulletgall wasp. In fact, I’ve seen more samples of it at our garden centre than ever before. It attacks a range of oak trees but is particularly bad on bur oak, which is by far the most prominent species of oak on the prairies. The life cycle of this wasp is fairly simple and representative of most gall wasps. Adult wasps lay eggs in leaf-buds, and by early summer of the following year, the developing larvae cause galls to grow and envelope them. By late summer, the galls grow to a marble size and exude a clear, sticky secretion called honeydew. At this stage of the cycle, you’ll often notice that the gall wasps’ burger-eating cousins often swarm the honeydew-covered galls. Although these intimidating onlookers are of no harm to your trees, the words swarming and wasps don’t provide much comfort when used in the same sentence. The bulletgall wasp’s life cycle is finally completed when a single adult wasp emerges from each gall, mates, and the females once again lay eggs in the leaf-buds.
Control issues
How you control your gall wasps will have a lot to do with the species of tree or shrub you’re dealing with. Roses can be treated fairly easily by simply snipping off the effected branches, but when dealing with trees, a thorough spraying of horticultural oil is required to kill the over-wintering gall wasp eggs. But how does one thoroughly spray a 20-metre oak? It takes some specialized equipment to reach and completely coat the upper branches with oil—a task that often requires a professional arborist. The good news, however, is that the galls don’t seem to cause any long-term damage to most trees and shrubs, so living with the problem is often the simplest solution. It may not be the most aesthetically pleasing option, but you have to admit that gall wasps do create fairly interesting blemishes. Hmm…perhaps if you’re lucky, some pesky squirrels will mistake the galls for acorns and solve the wasp problem for you. Wishful thinking never hurts.
