Rose rosette disease, lethal to multiflora rose and indigenous to North America, has been proposed as a biocontrol agent for multiflora rose, a noxious weed in the central and eastern United States. Studies in experimental plots showed that the disease can be intensified by grafting infected shoots onto plants in established stands (i.e., augmentation). The rate of disease spread in augmented plots was significantly faster compared to epidemics in nonaugmented plots at 5 locations. Augmentation provided effective control 3 to 5 yr after implementation. Risk to ornamental rose seems to be low under conditions of this study. Plots to assess risk of the disease to ornamental roses, located at distances greater than 100 m from augmentation sites, showed no infection during the 3 yr of this study.

Multiflora rose is a serious weed pest in West Virginia. There are cultural and chemical means for control, but expense and environmental consequences often preclude their use. Limited information is available concerning biotic agents with potential for multiflora rose biocontrol. A literature search, contacts with scientists in Asia where multiflora rose originated and apparently is not a pest, and disease and insect surveys in West Virginia indicate this plant is healthy and, generally, pest free. However, three insects in West Virginia and one disease occurring in the midwestern United States were of special interest. The rose hip borer, Grapolita packerdi Zeller, which consumes the hypanthium tissues of the hips; the rose seed chalcid, Megastigmus aculeatus var. nigroflavus Hoffmeyer, which destroys the seeds within the achenes; and the raspberry cane borer, Oberea bimaculata Oliv., which kills canes, were found in West Virginia. The disease, rose rosette, not found in West Virginia, is killing multiflora rose in Arkansas, Indiana, Kansas, and Missouri. There is little information on the biology and/or host ranges of these insects or the disease. However, finding three insects in West Virginia adversely affecting growth and/or reproduction of multiflora rose and learning of a disease that kills this plant suggest there are biotic agents that might help manage multiflora rose.

Multiflora roses showing symptoms of rose rosette were found in nine counties in southern Indiana and two counties in northern Kentucky. The eriophyid mite, Phyllocoptes fructiphilus Kiefer (Acari: Eriophyidae), implicated as the vector of the rose rosette agent, occurred on most symptomatic material. Another eriophyid mite, P. rosarum Liro, was found on symptomatic material collected in Kentucky. Transmission of the causal agent into multiflora rose by shield budding and by P. fructiphilus was successful. The rose rosette agent appears to be spreading east and is established on multiflora rose in the Ohio Valley.

Multiflora rose is a major weed in pastures, highway embankments, and recreational areas. A chalcid wasp, Megastigmus aculeatus (Swederus) (Hymenoptera: Torymidae), which feeds on the multiflora rose seeds, is a potential biological control agent for this weed. Distribution of multiflora rose and the seed wasp was studied from 1983 to 1986 in Virginia. Multiflora achenes collected from 58 sites in 51 counties showed that M. aculeatus was present in all but one of the counties surveyed; female:male sex ratio was high (94:1), indicating parthenogenesis. Infestation rates of the achenes averaged 26.5% in 1985 and 23.9% in 1986. Severe winter temperatures appear to affect the wasp population adversely.