Boring Insects That Attack Roses

Borers are among many insect species that prey on roses.

Various boring insects are among the primary pests of roses (Rosa spp.) in the United States. Borers are the larval form of various insects, including beetle and moth species, that drill into the rigid stems, called canes, of rush bushes. Not all borers pose a serious threat to a large crop of roses, but a few target rose bushes specifically and are capable of causing widespread damage.

Raspberry Cane Borer

The raspberry cane borer (Oberea bimaculata) is a small beetle species that primarily infests raspberry plants, but they can also attack roses if their preferred host is not present. Adult beetles are dark black and less than an inch long. Females carve a small opening in their host's canes and deposit their eggs on the surface. Upon emerging from the eggs, the larvae tunnel directly into the plant's stems. They take shelter there as they complete several stages of their development. Damage done to the plant's circulatory system can be evident in less than a week as growth attached to the infested stems begins to wilt and die. The larvae also feed on the roots of their host, depriving them of water and nutrients.

Rose Stem Borer

The rose stem borer (Agrilus aurichalceus) is a significant insect pest that prefers to prey on rose bushes. According to the University of Minnesota Extension, these larval worms penetrate rose canes and carve winding paths down entire shoots. The leaves attached to infested canes often become discolored, making them easy to distinguish from canes supporting healthy growth. These worms also cause the formation of galls, malformed sections of dead tissue, near the base of damaged canes. Damaged growth should be removed as soon as possible to prevent the insects from maturing or attacking neighboring plants.

Tobacco Budworm

Tobacco budworm (Helicoverpa virescens) is a notorious pest of commercially cultivated tobacco and cotton in the United States, but it also threatens rose bushes and a variety of other garden plants. These pests, which are the larval form of a moths species, infiltrate the base of budding and opening flowers. Damage caused by these caterpillars prevents flowers from opening, which mars the beauty of ornamental plants, like roses, and prevents the formation of fruit on vegetable plants.

Pacific Flatheaded Borer

The Pacific flatheaded borer (Chrysobothris mali) is another prolific pest found throughout North America. It has a wide range of potential hosts and is known to attack both shrubs and trees. According to the Washington State University, damage caused by just a single one of these borers can fatally damage a young tree. The larval form the insect is a cream-colored worm that is roughly 1 inch long. The larvae penetrate the canes, branches or trunk wood of their host plant to feed on the softer tissues inside. The adult insects are brown and black beetles that are roughly half as long as the larval worms.

References

• University of Guelph; Insect Pests of Roses; Paula C. Richards; June 2000
• Washington State University; Pacific Flatheaded Borer; Hugh W. Homan
• University of Minnesota Extension; Roses for the North: Insects; Kathy Zuzek et al.; 1997
• Colorado State University Extension; Tobacco (Geranium) Budworm; W.S. Cranshaw; November 2006
• University of California: Pests in Gardens and Landscapes, Rose-Rosa Spp.