Rose Cane & Wasp Nests

About

• Pemphredon wasps are small, black wasps about 1/4-inch long. They prey on other insects, especially aphids. Females establish their nets by making a small tunnel into the cane of roses and other plants. They then fill the cell with about a dozen paralyzed insects, usually aphids. Once this is done, they lay a single egg before sealing up the chamber with chewed pith. When she is done, the female repeats this process in another location.

Symptoms

• The first symptom of cane borers are small tunnels at the end of pruned canes. Eventually, leaves at the top of the bush may wilt and turn yellow. Canes may brown, lose their leaves, and die back as well. A small bulge may appear at the nest location. Cane borers rarely kill rose bushes, but they can weaken canes, causing them to break in the wind.

Prevention

• Preventing cane borers is a simple, but somewhat tedious, process. After pruning, seal your canes with Elmer's glue or water-soluble wood glue. The water-based glue will not burn the plant. Adding a few drops of food coloring to the glue can help you keep track of which canes you have sealed. Glue can be spread with a paint brush or small cotton swab. Other substances you can use instead of glue include fingernail polish, pruning sealant or orange shellac.

Control

• If the rose borers are doing significant damage to your rose plants, then control is necessary. Although chemical control is an option, it is not recommended by Stephen Scanniello, author of "A Year of Roses." Instead, control can be achieved by pruning and sealing canes. Inspect canes until you find one with a hole in the end. Cut the cane back an inch at a time until the hole is no longer visible. If you come across a white worm, or larvae, kill it by squashing it. Seal the cane with glue or fingernail polish.