Several rose pests can be described as "green worms." They all inflict similar damage, whether it is defoliating bushes or eating new buds. Chemical control is rarely effective at controlling these pests. Whatever control you can offer with your own two hands by removing these larvae yourself may be the best method of control. Identifying the pest in question can lead you to the right solution, but don't hesitate to remove whatever you see before taking the time to identify them.
Identifying Sawfly Larvae
Sawflies and their larvae are some of the most pervasive and pesky of the rose pests. The light green larvae are about 1¼ inches long. Sawflies are small, dark, non-stinging wasps. Their larvae feed on rosebush leaves, and it doesn't take long for them to devour the greenery. They are differentiated from caterpillars by the number of prolegs (legs behind the front three pairs). Sawfly larvae have five or more pairs, while caterpillars have fewer. They are also called rose slugs.
Leaf-Rolling Caterpillar Damage
Female leaf-rollers lay their eggs in rose leaflets and secrete a chemical that induces the leaf rolling. The caterpillar larvae feed within the safety of the leaf roll. The rolling occurs soon, within 24 hours of an egg deposit. The leaves do not fall off but remain on the bush for the remainder of the season. Remove and destroy affected leaves immediately.
Identifying Rose Budworms
Rose budworms are little green worms that are rarely seen. If you notice that new buds have holes and are eaten inside, then the problem is most likely rose budworms. The larvae live in the bud, essentially eating their way out, and pupate in the ground to emerge as adults. Again, if you can catch it early, remove the affected buds immediately to keep it under control.
Introduce Birds and Wasps
Many people do not want wasp nests in their backyards for fear of being stung, but the truth is that wasps are highly beneficial insects because they eat the bugs and larvae that damage your roses. At the same time insects are developing, birds are nesting, which means there are a lot of hungry babies to feed, and those protein-packed larvae are just what they want. Begin by letting wasps nest on or around your house. If you don't like the spot they choose, destroy it while it is still small and encourage them to build elsewhere. By simply providing a birdbath with a battery-operated bubbler (birds love moving water) you will attract all the bluebirds, chickadees, grosbeaks, woodpeckers and warblers you need to get rid of whatever infestation plagues your roses.
If you monitor your rosebushes closely and routinely, you should be able to catch an infestation before it devastates your plants. Often the underside of leaves is where these hungry pests hang out, so lift the leaves and pluck off what you see. You will have to destroy the larvae by either squeezing them between your fingers or dropping them into soapy water. If the entire idea of handpicking is distasteful to you, try attacking the pests with a strong stream of water (early in the morning so the plant has time to dry out during the day) or spraying the rosebush with an insecticidal soap.