We have bush type roses that grow on the south side of our home. Over the past few years we have noticed they are becoming infested with some type of pest that creates pods on the stem. It seems to suck the life out of that stem and moves on to another. Inside these pods are small worms. We have done some dusting in the past, with little luck. We trim out the infested stems, but it seems as this is becoming a losing battle, as more appear. What are these little pests and how can we be rid of them?
Several boring type insects can cause the stem swelling you describe. The adults are flying insects that lay eggs on the rose stems. The eggs hatch and the larvae (immature stage) tunnel into the stem, feed and cause the swelling. Many just feed in the pith and cause minimal damage to the health and vigor of the plant. Many rosarians cover cut stems with a drop of white glue to seal the wound and keep out the pith borers. Stem girdlers feed under the bark and can cause the infested stem to wilt and die. Regular pruning, removing older canes in suckering roses, will help reduce the risk. Continue to prune out the swollen areas as soon as they are discovered. There is no effective chemical treatment for this pest.