‘R. multiflora’ & Rose Rosette Disease The White Menace ‘R. multiflora’ & Rose Rosette Disease The Good, The Bad, The Ugly

This Program Services Committee presentation created by: Mary Peterson Master Rosarian

‘R. multiflora’ Multiflora rose is a non-indigenous rosaceous plant that is native to East Asia (Japan, Korea, and eastern China) It has been introduced into North America many times since the late 1700s as garden plants and as root stock for ornamental roses. It was widely planted in the 1940’s to 1960’s in the eastern United States as a wildlife plant for erosion control and as a living fence. Panicles contain six to 100 (average of 63) hypanthia or hips that are glabrous to pubescent, develop during the summer, and become bright red by mid-September; hips contain an average of seven achenes. Each large cane can potentially produce up to 17,500 seeds. Seeds remain viable for a up to twenty years. In Iowa it is estimated that more than one million acres of pastureland and wildlife areas have sustained significant degradation as a result of colonization by ‘Rosa multiflora’. The principal area of infestation are 61 counties; nearly two thirds of the counties in Iowa.

Plants of ‘R. multiflora’ R. multiflora is a perennial shrub that grows 6-10' tall, up to a maximum of 20'.  They form dense clusters of shrubs, spanning as much as 30' across.  The many stems originate from the base, growing upright. They then arch over and become almost trailing.  The stems grow up to 13' long.  Along the stems are stiff curved thorns.  The alternate leaves are 3-4" long.  They are pinnately compound, typically with 7-9 leaflets but may have anywhere from 5-11 leaflets.  The leaflets are 1/2 to 1"ovals with toothed margins.  The top of the leaflet is smooth whereas the bottom is covered with short hairs and is paler. Plants of ‘R. multiflora’

Fields overgrown with ‘R. multiflora’ Originally, this plant was brought here to be used as rootstock for cultivated roses. Since then, it has been the "solution" to various problems.    In the 1930's, the United States Soil Conservation Service strongly recommended planting this species to prevent erosion. Concurrently,  the nursery industry was advertising it as the perfect solution to fence in cattle and to create a natural crash barrier along the highway.  Later, in the 1960's, wildlife biologists were recommending this plant as a good source of food and shelter for the fauna.  Until recently, humans have been the main spreader of this plant.  The primary reason that this plant has become so successful is the widespread and intense distribution by humans.  We planted this shrub in various habitats across the United States. In addition, this shrub has many characteristics that further helped it succeed in dominating the landscape.  It is capable of propagation in two ways: by seed, or by the formation of roots when a stem touches the ground. This allows the plant to reproduce asexually even when conditions may not be right for flowers to form.  When it does flower and fruit, up to 500,000 seeds can be produced. These seeds can remain dormant in the soil for up to 15 years, so it can appear years after it was thought to have been eradicated.  The fruits are appealing to birds and mammals which carry the seeds to new locations.   Costs of conventional control methods are high ($50 to $200 an acre) and there are concerns about water contamination effects of repeated application of herbicides to pasturelands. Biological control methods would be less environmentally costly because they are better targeted and run no risk of added pollution to groundwater. The difficulty with biological control lies in identifying pathogens and pests with minimal or no risk to non-target organisms. Fields overgrown with ‘R. multiflora’

Flower clusters of ‘R. multiflora’ Photo by John Lynch Say everything’s coming up roses, and it is generally a positive statement, unless you are talking about multiflora roses. Multiflora rose comes up everywhere and is so widespread and familiar that many do not realize it is a troublesome and costly invasive non-native plant. R. multiflora blooms in late spring with white or light pink flowers 1/2 to 3/4" across.  The flowers often form a panicle 1 to 1 1/2" wide. In the late summer, the fertilized fruits form.  These red fruits are round or ovoid, approximately 1/4" in diameter, and persist throughout the winter, often until spring.  The seeds inside the fruit are angular achenes.     

Panicles of ‘R. multiflora’ flowers Photo by James Miller These species are called 'invasive exotics' because their growth rate is aggressive and rapid. They tend to leaf-out before native plant species, and thereby shade emerging native plant species. This shading factor further retards the growth of native plants, and gives the exotic invasive species a head start on the growing season. As a result of this aggressive growth factor, invasive exotics are out-competing native plant communities. Panicles of ‘R. multiflora’ flowers

‘Achenes’ or rose seeds of ’R. multiflora’ Multiflora rose is named for the clusters of many white flowers borne on this perennial bramble during May or June. The flowers develop into small, hard fruits called hips that remain on the plant throughout winter. The great majority of plants develop from seeds remaining in the soil relatively close to plants from which they were produced. Birds and mammals also consume the hips and can disperse them greater distances. Rose seeds may remain viable in the soil for 10-20 years. Multiflora rose also spreads by layering, i.e., where tips of canes touch the ground and form roots, and by plants that arise from shallow roots. ‘Achenes’ or rose seeds of ’R. multiflora’

Northern Mockingbird and Multiflora Rose Hips Photo by Johann Schumacher Distribution by birds and other mammals (deer) is difficult if not impossible to control. Robins, mockingbirds, starlings, red-winged blackbirds and other species feed heavily on multiflora rose hips in fall and winter. Passage of seeds through digestive tracts of songbirds increases the germination rate, while bird feces provides fertilizer to seedlings.

Distribution of ‘R. multiflora‘ (green areas = areas of ‘R Distribution of ‘R. multiflora‘ (green areas = areas of ‘R. multiflora’) (white areas = none reported) In eastern North America, multiflora rose is abundant from the Great Plains (where the species has been planted as wind breaks) to the east coast. It occurs from northern Texas, Arkansas, Mississippi, Alabama, and Georgia in the south, north to the New England coast, central New York, southern Michigan, Wisconsin, and Minnesota. It occurs only as plantings south of central Georgia, probably because of the lack of cold temperatures needed to stimulate seed germination. The plant’s northern distribution is limited by its sensitivity to severe cold temperatures. ‘R. multiflora’ grows native in Korea, Eastern China and Japan.  It can now be found all over the northeast and midwest United States. It has been found almost everywhere except in the Rocky Mountains, the Southeastern Coastal Plains and the Nevada and Colorado desert. R.multiflora was brought to the United States in 1886 from Japan   It was introduced on the East coast. R. multiflora can survive and thrive in a variety of habitats.  It is found in prairies, savannas, open woodlands, forest edges, old or abandoned fields, mature forest, roadsides, etc.  Its soil and environmental requirements are broad, but it prefers well-drained soils and good sunlight.  The only conditions it is not found in is extreme cold, with an intolerance to temperatures below -28` F, dry or wet areas.  

‘R. multiflora’ infected with Rose Rosette Multiflora rose is highly susceptible to rose rosette disease, so much so that the disease was initially considered a potential biological control for multiflora rose. Even now, some people suggest introducing infected plants into areas with multiflora rose to control this weed. Most rose growers, however, are very wary of this recommendation because rose rosette disease can spread quickly from multiflora roses to cultivated roses. Photo by S. Debolt

“Witches Broom” Photo by M.A. Hansen Since the new leaves of many rose cultivars normally have reddish pigments, it may be difficult to determine whether the reddish color is abnormal or not. Therefore, it is important to continue to monitor symptoms on suspect roses. On RRD-infected plants, the reddish color does not go away, whereas on healthy plants, the reddish color usually disappears as the leaf matures. Witches brooms on some diseased plants may be an unusual color of green that can be mistaken for symptoms of nutrient deficiency. However, nutrient deficiency should affect the whole plant. If these symptoms appear only on parts of the plant, they are probably not due to nutrient deficiency, and RRD is more likely. The witches broom symptoms itself is not necessarily diagnostic for RRD. This symptoms can also occur in response to certain types of herbicide injury. Photo by Ann Peck Photo by James W. Amrine Jr.

Photo by M.A. Hansen If glyphosate, the active ingredient of the herbicide Round Up®, contacts green tissue of rose plants in the fall, it is translocated to the buds, and symptoms do not become evident until those buds emerge the following spring. Witches brooms with yellow, narrow leaves on clusters of shoots are typical of glyphosate injury. The commonly used broadleaf herbicide 2,4-D can also cause leaf distortion on roses. Unless plants are injured again, symptoms of herbicide injury should disappear by the following year. Abiotic damage to foliage from RoundUp® Photos by Baldo Villegas Entomology Dept. UC Davis

Reddish aberrant new growth on modern roses infected with RRD The disease is known to be transmitted by the eriophyid mite Phyllocoptes fructiphylus or by grafting. The wild multiflora rose (Rosa multiflora) is very susceptible to the disease and is a common source of inoculum. Cultivated roses planted downwind of infected multiflora rose are especially at risk because the mite vector travels on wind currents from infected to healthy plants. Some growers have observed symptoms on previously healthy plants within four weeks of being planted downwind from diseased multiflora rose. Photos by Ann Peck

Typical Rose Rosette growth on ‘R. multiflora’ roses Rose rosette disease (RRD) was first reported on Multiflora roses at the Morden Research Center in Morden, Manitoba, Canada in 1940.  The first report of the disease in the Midwest occurred in 1968 in Nebraska.  There were few additional reports of the disease in the central U.S. until 1976 when the disease was identified  on cultivated roses and multiflora roses in Kansas and Missouri.  A survey conducted in 1999 reported occurrence of the disease in Iowa, Nebraska, Kansas, Colorado, Utah, California, Missouri, Arkansas, Illinois, Indiana, Ohio, West Virginia, Pennsylvania, and Tennessee. Photo by Chris Evans

Distorted bud formation on a modern rose infected with RRD The causal agent of rose rosette disease is not soil-borne, so it is possible to successfully plant healthy roses in beds where diseased plants have been removed; however, the pathogen may persist in old root pieces that remain in the soil from previous diseased roses. If plants regrow from these old root pieces, as multiflora rose is apt to do, they can serve as an inoculum source for healthy plants. Therefore, it is important to remove old plants thoroughly and ensure that infected plants are not allowed to regrow from old, infected root pieces. Flowers that are normally a solid color may be mottled. Buds may abort, be deformed, or be converted to leaf-like tissue. Infected rose plants often die within one to two years. Photo by S. Debolt

Typical Red New Growth of RRD Infected plant Photo by James W. Amrine Jr. Considerable research with RRD was conducted in the 1980’s and early 90’s, and while much was learned about the disease, wide gaps in our knowledge remain.  RRD is able to infect most species of the Rosa genus, whereas other plants in the Rose family appear to be tolerant to the disease organism.  Within the Rosa genus there is considerable range in susceptibility, with Multiflora roses appearing to be most easily infected and most susceptible.  The earliest symptoms of RRD are development of a deep red color on the undersides of leaves.  Affected stems may grow vigorously with a pink to magenta coloration.  Later symptoms include small, distorted leaves with a bright red coloration..  Leaf petioles are shortened and affected stems develop a rosette appearance.  Plants generally survive for two to five years following development of initial symptoms before eventually succumbing to the disease.

Twisted stem growth on RRD infected plant Twisted stems and aberrant reddish twisted foliage is indicative of RRD.

Symptomatic thorns on roses caused by rose rosette Photo by Jim Yearwood These pictures are typical of the extreme thorniness that RRD produces. Photo by S. Debolt

Mowing and burning operation Rose bushes cut with a chain saw during the winter months Physical Control of stands of ‘R. multiflora’ Pulling, grubbing, or removing individual plants from the soil can only be effective when all roots are removed or when plants that develop subsequently from severed roots are destroyed. In fire-adapted communities, a routine prescribed burn program will hinder invasion and establishment of multiflora. Research indicates that 3-6 cuttings or mowings per growing season for more than one year can achieve high plant mortality. Such treatment may need to be repeated for 2-4 years. Increased mowing rates (+6 per season) did not increase plant mortality. In some areas, repeated cutting is preferred over mowing because repeated mowing will damage native vegetation as well as multiflora rose. Mowing and burning operation After spending approximately 2 months cutting Multiflora rose bushes, burning them was very satisfying

Biological Control of RRD Mites over winter as adult females on living, green rose tissue. In early spring, the mites move from wintering sites (clumps of over wintering foliage, loose bark on live stems, old or loose bud scales, etc) onto developing shoots to lay eggs. A favorite oviposition site is between the stem and basal petiole of young leaves. Females live about 30 days and lay about one egg per day. Eggs hatch in three to four days and the development of each immature state requires about two days. Thus, in warm weather, one generation may be produced per week. Development is continuous throughout the season until weather turns cold in the fall and mites seek protective wintering sites on the plants. Over wintering mites will die if host canes die, as they require green stem or leaf tissue to survive. Eriophyid Mites

Microscopic Eriophyid Mites Phyllocoptes fructiphilus Keifer Phyllocoptes fructiphilus Keifer Several types of biological controls exist already or are being tested. Rose rosette disease, carried by the mite Phyllocoptes frutiphilus , is a native virus that is fatal to R. multiflora.  Unfortunately, it is also kills our native roses, in addition to commercial species such as apples, berries, and cultivated roses.  Although it is not recommended to increase or introduce this disease, it may naturally infect this shrub. Phyllocoptes fructiphilus Keifer

Rose Stem Girdler Agrilus aurichalceus (Coleoptera: Buprestidae) Photo by Whitney Cranshaw Girdled cane caused by larva Photos by James W. Amrine Jr. The rose stem girdler beetle (5-9 mm long) has also been found to negatively impact this invasive plant. It chews a ring around the stem of the plant, killing it.  It should be kept in mind that although these methods are 'natural' they all have the potential to strongly impact native roses or other species in the Rose family.   The rose stem girdler [Agrilus aurichalceus (Coleoptera: Buprestidae)] may be of lesser importance, but in concert with the others should further enhance biocontrol. The larvae girdle can kill individual canes, not whole plants. Developing rose hips (fruits) and seeds above the girdling will die. This biological agent is likely to spread and colonize all stands in possibly 20 or more years, eventually destroying the viability of 90% of yearly seed production. Agrilus aurichalceus (Coleoptera: Buprestidae) Close up of girdle and broken cane A "flag" caused by the break of a cane at the girdle

Rose Seed Chalcid Wasp Photo by James W. Amrine Jr. Another control method is the European rose chalicid wasp, Megastigmus aculeastus nigroflavus .  This non-native has been found in nurseries on the East coast, apparently brought in with imported rose seed and was reported in New Jersey in 1917.  These wasps lay one egg in the fruit, which hatch into larvae. The larvae consumes the contents of the seed.  In the late spring, the adult emerges.  It is a weak flyer with a short lifespan.  The adult completes the lifecycle, theoretically on the same plant or in the same thicket, effectively destroying the plant over several generations. Photo by James W. Amrine Jr.

Rose Seed Chalcid The rose seed chalcid (Megastigmus aculeatus var. nigroflavus) has been shown to be widely distributed where multiflora rose is found in the United States. The chalcid, more prevalent in eastern states than Midwestern, is spread by birds and is catching up to the widespread distribution of multiflora rose. The small torymid wasp lays eggs within seeds, rendering them sterile. This biological agent is likely to spread and colonize all stands in possibly 20 or more years, eventually destroying the viability of 90% of yearly seed production. This would become a powerful biological control, especially where rose rosette is also present.

Seed parasitism by the Chalcid Wasp The adults vary greatly in size and coloration. Wasps that are raised from a wild or multiflora rose are considerably smaller than those raised from the larger cultivated rose. Typically, they are approximately 3 mm in length and are mostly yellow in color. The females carry an ovipositor that curves upward from the last abdominal segment and is about the same overall length as the wasp. Brown patches are on top of the head surrounding the ocelli, on the sides of the thorax, and on the dorsal side of the abdomen. The elbowed antennae are also brown and have eleven segments. The males are typically smaller, darker to nearly black in color, and do not have an ovipositor. The eggs are oviposited into rose hips during June and July. The larvae feed entirely within the rose seed and can grow to 2.8 mm or slightly more than 1/10 inch in length. The size, however, is greatly dependent on the size of the seed. The larvae become fully grown in the fall and remain within the seed casing until the following spring when they pupate. The adults emerge from the seed by chewing small openings in the seed in early summer.

Rose hips damaged by Chalcid wasp In Asia, the chalcid may infest 95% of the achenes or seeds. Chalcids have limited ability to fly to newly established rose plants. Most dispersal is by movement of infested seed by birds; seed chalcids rapidly pass through the gut unharmed if the seed is eaten by song birds.

Cold Weather Affect on New Rose Growth This may be the result of a late frost while roses are in the active growing stages. It is also thought that Spring Dwarf Disease may also be viral in nature. These samples are not RRD. Spring Dwarf Disease?

‘R. multiflora’ and RRD Early Identification of RRD infected ‘R. multiflora’ Physical Control – cutting/burning Herbicide/Chemical – Round Up, Krenite, Banvel Biological Control – Eriophyid Mite Rose Seed Chalcid Rose Stem Girdler Garden roses should not be planted within 100 yards or downwind of stands of Rosa Multiflora. Repeated cutting and proper disposal of infected multiflora can be effective. Chemical eradication can be both expensive and a concern to the ecological health of other plants. The use of Eriophyid mites that may infect garden roses is a concern to rosarians. The only known control of the mite presently is Cygon 2E. There is no known control for Rose Seed Chalcid or Rose Stem Girdler.

What The Future Holds… The reduced populations of multiflora rose remaining after the RRD epidemic are likely to be infested by the seed chalcid at the same rate (90-95%) as plants in Korea and Japan. Multiflora rose will then be another occasional plant in the environment, and not the noxious weed that it is today. It is estimated that this scenario will transpire within the next three to five decades. Farmers and others wanting eradication of multiflora rose desire human intervention to increase the rate of spread of the disease, the mite and the torymid into uninfested areas. However, many rosarians desire that all augmentation work with RRD and the mite cease. The rose seed chalcid could be intentionally released in areas wherever infestation rates are below 50-60%. Risk to other rose species from this seed chalcid appears to be minimal. Even if not deliberately spread, its range will increase by birds. Eventually, multiflora rose will be reduced to low levels, occurrence of RRD will become minimal and problems for farmers and rosarians alike should be greatly reduced. It is virtually certain that RRD will greatly reduce the density of multiflora rose. No multifloras have been found that are resistant to the disease. Millions of dollars now spent annually by farmers in many eastern states to control multiflora rose will be saved when the plant is eventually controlled. In West Virginia, during 1980-1981, more than 36,500 hectares were heavily infested with multiflora and a ten-year eradication program using herbicides was estimated to cost more than $40 million. Managing the weed with herbicides is costly and can have serious effects on nearby trees and contaminate water tables. The same or increased acreage is now infested, and allowing for inflation this cost has probably doubled. However, monetary savings will be slow to develop because of the slow natural spread of both the epidemic and biological control agents. One problem with using the rose seed chalcid is that it is not specific for Rosa Multiflora and rose hybridizers who have fertilized hips in the growing fields might be impacted by having all their rose hips rendered sterile by this insect.

Additional Considerations… Dr. Keith Zary (VP of research for Jackson & Perkins) has encouraged breeders to concentrate their efforts on hybridizing roses that are RRD resistant and RRD tolerant. A species called the McCartney rose, which exists as a weed in Texas, is susceptible to RRD but resistant to feeding by the mites that transmit the disease. It may be possible, through breeding techniques, to incorporate this mite resistance into cultivated roses in the future. In the meantime, it would be wise to assume that all cultivated roses are potentially susceptible to the disease and to be on the lookout for symptoms of rose rosette. We hope that this program will increase awareness of the dangers of Rose Rosette and that rosarians will keep a close eye on their gardens and roses growing in public areas. Proper identification and early intervention are two powerful tools available to the rosarian presently.

Program Services Committee John Mattia, Chairman Jolene Adams Richard Donovan Pat Hibbard Larry Peterson Mary Peterson Diane Schrift

Program Services Power Point programs on roses are available for download from the ARS website, ‘members only section.’ They are offered to our members for use by a local or district rose society or an ARS judging or consulting rosarian school. These programs are copyright © ARS 2007 Commercial use is strictly forbidden.

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