The Q&A Archives: Insect boring rose stems

Question: A bug is boring into the pruning cuts on my rose stems, killing about 4 inches of the stem. What is it and how do I stop it? Debbie Tuck McMinnville, OR

Answer: Although many insects can bore into rose stems, the most common one to bore into pruning wounds is the carpenter bee, says Lorrie Coletti, horticulturist at Jackson Perkins Nursery, specialists in roses in Medford, Oregon. The adult carpenter bee resembles a bumblebee, but it overwinters in wood and emerges in May and June. The adult female bee chews into the pith of rose stems at pruning cuts. It lays eggs in the pith, where the larvae feed for a few months until pupating. There is usually only one generation a year. The carpenter bee is attracted to pruning cuts because they offer easy access to the soft pith, says Coletti. Canes that are more than 1/4-inch diameter are most susceptible to the bee damage. The best control is to remove thelarvae by cutting away the infected stems just below the blackened area where the bee has been feeding. After pruning the stems, dab a white glue, such as Elmer's, on the pruning cut to seal it. We've found white glue is the only sealant that keeps the bee from penetrating the pruning cut, says Coletti. Apply the glue after each pruning no matter what time of year. Even though carpenter bees are most active in spring, they will attack old cuts.

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