Something bored into the canes of my rose bushes last year, leaving hollow openings at the ends wherever I made a pruning cut. This spring I notice that a lot of those canes have died back. What’s doing it?
There are a number of species of bees and wasps that burrow into soft or dead wood to create nesting places to lay eggs and raise their young. These are solitary insects, not colonizers like honeybees. Although they usually seek out decaying wood to make their nests, the pithy heart of a rose cane is soft enough to invite their attention.
One species of burrowing bee is the leaf cutter bee, which leaves more obvious evidence of its presence in the dime-sized, semicircular holes cut into rose leaf edges. These bees are important pollinators, so while you might want to shoo them away from your roses, please don’t go about it by using anything toxic.
You can discourage bees and wasps from setting up household in your rose garden by dabbing a bit of grafting wax (buy it from an agricultural supply retailer) on each cut as you prune your roses, cut bouquets, or deadhead. Some rose gardeners report that a drop of white glue on each pruning cut also works—but it would have to be a type of glue that doesn’t wash away in the rain.
The damage from leaf cutter bees is usually insignificant and doesn’t compromise the plant’s health or vigor. You might decide that applying grafting wax—a messy and tedious task—is worse than simply pruning away the occasional damaged cane. —Doug Hall