Quite a few insects can choose to make your rose bush their home but only a few are really harmful. Recognizing the signs of insect damage and matching that to the insect that caused it will put you on the road to treating the problem. Proper maintenance can go a long way in deterring insects from selecting your rose bush but if they do, you’ll be able to recognize them.
Types of Insects
Different parts of the rose bush are attractive to different types of insects. Defoliation can be caused by insects that chew on leaves, cut holes in them or remove layers from the leaf. Other insects suck the sap from the plants leaving them lacking in water and food. Flowers and flower buds are attractive to another group of insects who eat the petals and buds or lay eggs in the buds. Another group lays eggs inside the stem or cane, effectively killing the portion of the cane above the infestation.
The nature of leaf damage leaves clues as to which insect caused it. Some simply chew irregularly shaped holes in leaves like the rose slug and curled sawfly larva. Others like the adult rose sawfly leave behind what looks like the skeleton of the leaf by removing a layer of leaf from between the veins. All that remains is a thin, transparent layer and the veins, creating the skeletal appearance. To line their nests, leaf cutting bees remove round, smooth edged holes from the middle of leaves.
False Japanese beetles feed on flowers and buds as do Japanese beetles but the latter also feeds on leaves. The Hoplia beetle is drawn to and feeds on light colored flower petals. The Rose curculio is a weevil that leaves holes in buds and flowers, most often in white and yellow roses.
Die Back Injuries
Flatheaded borers and raspberry horntails both attack canes and can cause the plant above the infestation site to wilt and die. Borers are drawn to pants that are already stressed or have bark damage. Horntails lay eggs inside the cane and cause a gall to form. The plant is girdled at this point and the cane will die above the site.
Many insects are not actually harmful to the plant and are merely an annoyance. Bees, even the leaf cutters, are more beneficial than harmful and should be tolerated. As for the others, frequent inspection of the plant and applications of insecticidal soaps or other pesticides may be necessary. Always match the insecticide to the insect as insecticides are not “one size fits all”. Be sure to follow manufacturer’s directions for applying insecticide.
University of California: Insect and Mite Pests
University of Minnesota: Insect Pests of Roses