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July 2011

Welcome Biological Control or Dreaded Plant Pest?
Rose Rosette Disease

Contact: Robert B. Trumbule, Entomologist, Maryland Department of Agriculture | rtrumbule@rcn.com

rose rosette disease
rose rosette disease
Photos: Robert B. Trumbule, Maryland Department of Agriculture

ANNAPOLIS, MD (July 6, 2011) - Multiflora Rose, Rosa multiflora, a now common and widely recognized invader of old pastures, fencerows and right of ways throughout much of the Midwestern and eastern U.S. was once hailed as a hero of soil and wildlife conservation. Planting of multiflora rose was recommended by the US Soil Conservation Service from the 1930’s through the 1960’s. It was even touted as a “Living Fence”. In defense of this recommendation, multiflora rose was indeed a very hardy plant that readily colonized areas where planted and was good at seedling establishment and soil stabilization as well as beneficial for wildlife shelter and food…unfortunately the plant is too good in its success and has become the bane of managers of pastureland and right of ways. (see MISC Invader of the Month May 2006)

Nearly everything in nature, however, seems to have its own natural checks and balances, and a disease of multiflora rose began to be noticed in western North America as early as 1941 in California, Wyoming and Canada. This disease was given the common name “Rose Rosette Disease” (RRD). The introduction of RRD is linked with the introduction of multiflora rose stock to the United States from Japan which was imported to the U.S. as early as 1886. The disease causes stunting and a reddening discoloration of the new growth of multiflora rose, a growth pattern known as a “witches’ broom”. After as few as two or three and up to several years following onset of the disease, infected rose plants finally succumb and die. The disease is caused by a virus-like pathogen which is transmitted by a nearly microscopic eriophyiid mite; Phyllocoptes fructiphilus. This mite feeds on roses and is known to build up in very large numbers on multiflora rose. The disease moved from the western United States eastward, likely, for the most part as the tiny mites infected with the disease were carried by prevailing winds, and was in West Virginia by 1988 where it has been extensively studied by Dr. James Amrine of the West Virginia University.

RRD was monitored for and first detected by the Maryland Department of Agriculture (MDA) in western Maryland in 1996. At first the presence of the disease on multiflora rose was considered to be beneficial because of its ability to kill the tough invasive species which was difficult to control using either mechanical or chemical measures. However over the following 15 years, as MDA has monitored the continuing eastward spread of RRD, it has become apparent that many of our cultivated rose varieties are susceptible to the disease as well. Many popular varieties have been noted exhibiting symptoms of the disease with apparent susceptibility ranging from very susceptible (plants die in one to two seasons) through resistant (plants exhibit symptoms but live for several years) to apparently immune. In field trials conducted by MDA, ‘Flower Carpet” varieties have proven to be very susceptible, Meidland cultivars, including ‘Alba’ are moderately susceptible and the native species of roses; Rosa setigera, R. virginiana, and R. palustris and the naturalized R. rugosa seem to be very resistant to possibly immune to the disease. There are reports from the landscape and nursery trade in Maryland that other rose cultivars and species affected include, in no particular order: ‘Knockout’ , ‘Tamora’, ‘Zephrine Drouhin’ , ‘Collette’, ‘Snowbush’, ‘Kew Rambler’, ‘New Dawn’, ’Daybreak’, ‘Carmenetta ‘, ‘Clymenestra’, ‘Alexander Girault’, ‘America’, ‘William R. Smith’, ‘Zitkala’, ‘American Pillar’, ‘Snow Dwarf’, ‘Edmund Proust’, ‘Easlea’s Golden Rambler’, ‘Mrs. F.W. Flight’, ‘Edith Ballenden’, ‘Walsh Rambler’, ‘Madam Alfred Carriere’, and Rosa wichuriana hybrids.

While Maryland does not have a huge wholesale cultivated rose growing industry, roses are a favorite of gardeners and hobbyists and are an important component of the commercial retail nursery trade as well as of the landscape industry. It is unclear at this point as to what economic impact RRD may have on the green industry. Fortunately, along with the fact that several of the native species trialed by MDA were very resistant to potentially immune, there is hope for limitation of the effects of this disease in managed home gardens and landscapes. While there is no chemical measure that will directly control the causal agent of the disease, the eriophyiid mites can be managed. It is important to note, however, that not all miticides will control eriophyiid mites, so it is important to determine what mites are controlled when choosing a chemical control. Also, some of the horticultural oils and soaps seem to be somewhat effective at controlling mites. The key is early detection of mite populations and effective mite management as well as immediate eradication of any symptomatic plants. It is also advised that multiflora rose plants within the environs or surroundings of landscape rose plantings or commercial rose production facilities be removed. On the bright side, this disease may lead to a new level of breeding of roses for disease resistance, and after all, Rosarians, both professional and amateur, have been battling rose diseases and pests for centuries, so what is one additional challenge to them?

Thank you to contributors of information to this article including: Dr. James Amrine, West Virginia University, Mr. Nick Weber, Heritage Rosarium and; Ms. Leesa Green, Chapel Valley Landscape Co.

For more information, please visit:

Invasive.org

Virginia Cooperative Extension

For more information about Invasive Species of Concern in Maryland, visit www.mdinvasivesp.org

photos available electronically on request.

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