QuestionI was pruning my knockout roses when I noticed a worm crawling out of the center of the stem. I them noticed several of the stems had either a worm coming out or a hollow center where one might have been. What are they and what can I do about them. I live in the south.
Answer
Your roses have an insect called a rose cane borer. Cane borers are often noticed in the summer even though the infestation usually starts in the spring months. Often it will appear your canes are simply rotting and dying. It can be difficult to locate either the original larvae laying insect or the larvae inside the cane that抯 doing the damage. Most cane borers won抰 kill the entire rose. However insecticidal sprays don't help as the borer is protected inside the cane. The main method of control involves cutting the cane down past the borer, until you are left with only a healthy cane that is white inside. If the inside of the cane is brown or hollow you抣l need to trim down further. Once you抳e made your cut and are left with only a healthy cane you抣l need to close off your fresh pruning cut so a new larva doesn抰 reenter. The best way to do this is by covering your pruning cut with a dot of Elmer抯 glue. Nothing else will has an effect on cane borers other than pruning off the damaged canes and then sealing the pruning cuts. The insects and larvae will often over winter on your plants only to reemerge and start the cycle next spring. By keeping your roses pruned and sealed you can eventually lessen the cane borer population in your rose garden. Some gardeners put red food dye in the glue so they will know the canes they have already sealed.
