Rosa multiflora (multiflora rose), introduced to America from Japan for ornamental pur­poses 200 years ago, was promoted in Iowa during the mid-1930s as a  living fence  that would help to conserve soil and provide cover for wildlife. Multiflora rose has since natural­ized, and today some two million acres of Iowa land are infested with this pest, which renders pastures unusable (dense stands exist in coun­ ties south of a line from West Pottawattamie through Winneshiek, affecting the southeast­ern two-thirds of the state). Cattle avoid the prickly stems, and grass dies beneath its thick growth. Although tillage can control the weed, land in permanent pasture or under the Conser­vation Reserve Program is at risk for the spread of multiflora rose

Epstein, Abraham H.

Hill, John H.

Iowa State University Computer Science Technical Reports

Characterization of the Rose Rosette Disease causal agent: potential for biological control and multiflora rose

Rosa multiflora (multiflora rose), introduced to America from Japan for ornamental pur­poses 200 years ago, was promoted in Iowa during the mid-1930s as a "living fence" that would help to conserve soil and provide cover for wildlife. Multiflora rose has since natural­ized, and today some two million acres of Iowa land are infested with this pest, which renders pastures unusable (dense stands exist in coun­ ties south of a line from West Pottawattamie through Winneshiek, affecting the southeast­ern two-thirds of the state). Cattle avoid the prickly stems, and grass dies beneath its thick growth. Although tillage can control the weed, land in permanent pasture or under the Conser­vation Reserve Program is at risk for the spread of multiflora rose.</p

Epstein, Abraham

Hill, John

Digital Repository @ Iowa State University (ISU)

89-16 COMPETITIVE GRANTLeopold Center LEOPOLD CENTER FOR SUSTAINABLE AGRICULTURE Characterization of the Rose Rosette Disease causal agent: potential for biological control of multiflora rose Background Rosa multiflora (multiflora rose), introduced to America from Japan for ornamental pur­poses 200 years ago, was promoted in Iowa during the mid-1930s as a "living fence" that would help to conserve soil and provide cover for wildlife. Multiflora rose has since natural­ized, and today some two million acres of Iowa land are infested with this pest, which renders pastures unusable (dense stands exist in coun­ties south of a line from West Pottawattamie through Winneshiek, affecting the southeast­ern two-thirds of the state). Cattle avoid the prickly stems, and grass dies beneath its thick growth. Although tillage can control the weed, land in permanent pasture or under the Conser­vation Reserve Program is at risk for the spread of multiflora rose. In 1980 a state-initiated campaign (replaced in 1982 by a technical committee of the Iowa Department of Agriculture and Land Steward­ship, or IDALS) created a cost-sharing pro­gram to help landowners eliminate this prob­lem, and some herbicide manufacturers of­fered price reductions. However, because conventional control (repeated mowing and herbicide applications) was costly compared to the value of infested land, program partici­pation was low. However, interest in finding alternatives for multiflora rose control remains high among Iowa farmers. Commercial hybrid rose growers are also dis­advantaged by the proliferation of multiflora rose because it harbors pathogens and pests that threaten ornamental roses. However, one such pathogen, Rose Rosette Disease (RRD), also offers potential for reducing and control­ling multiflora rose. Endemic to midwestern states, RRD was first found in Iowa in 1986. It can now be found in virtually all multiflora rose stands in Iowa. Multiflora rose appears to be the preferred host of RRD. RRD occurs sporadically, however—it has eliminated mul­tiflora rose stands on several tracts of land in southern Iowa while leaving other stands un­affected. The goal of this project was to assess RRD's potential as a biological control agent for multiflora rose. This work investigated "augmenting" or arti­ficially intensifying RRD in a stand of multi­flora rose via grafting or other means to hasten the development of the disease. One year following infection (natural or augmented), infected plants go into the rosette stage (exhib­iting distorted leaves and shortened petioles). Once a plant is infected, it becomes highly conducive to build-up of high populations of the eriophyid (wooly) mite Phyllocoptes fructiphilus, the vector for RRD, which is transported primarily via wind. These mites then spread the disease to other plants in the stand. (As the virus spreads, the plants become susceptible to other diseases as well.) The mites thrive on RRD-infested plants, which become devoid of starch and high in protein as the disease progresses. This protein attracts the mites, which feed on the infested plants. But because the eriophyid mite does not over­winter well in Iowa, RRD has not spread well enough on its own to reliably eliminate multi­flora rose. The objectives of this work included deter­mining the extent of multiflora rose infesta­tion, the distribution of RRD infection in Iowa, the disease mechanisms in the plant, the host range of the disease agent, the character and identity of the causal agent, the disease's epi­demiology, means of disseminating the causal agent to achieve practical, field-scale multi-REPORT Principal investigator Abraham H. Epstein Co-investigator John Hill Plant Pathology Iowa State University Budget $47,508 for year one $11,330 for year two $49,653 for year three $8,000 extension for field trials Leopold Center Progress Reports 33 Transmission of RRD via grafting (note bud at center of photo) was highest from the end of May through mid-July; it was also highest on current season growth. flora rose control, and risks associated with RRD as a biological control. Approach and methods Investigators used experimental plots estab­lished in 1986 in natural multiflora rose stands in southeast Iowa. Plots in both open and shaded areas consisted of a small group of symptomatic plants to provide an inoculum focus for new infection of 25 nearby healthy plants. The asymptomatic plants were tagged and observed monthly each growing season from 1986 through 1991. Ornamental rose plantings were also observed for RRD symp­toms in several Iowa locations. Host range studies: Vegetation in and around the experimental plots was observed for ab­normal symptoms. Four additional plots es­tablished in 1987 were observed for RRD augmentation studies on rose and effects on related plants. These plots also consisted of one naturally infected multiflora rose plant in the rosette stage as an inoculum source at the center with four each of the test plants planted around the inoculum source. Various rose-related plants (including apple, peach, pear, cherry, strawberry and raspberry) were tested, as were several varieties of rose including multiflora rose. The same plant varieties that were used in the field studies were also tested in the greenhouse. Plants were then observed for development of symptoms for two years. Transmission to multiflora rose: Transmis­sion of RRD to multiflora rose via grafting was studied in both the field and greenhouse. In the field, 20 grafts (two per plant) were made at each of two locations at two-week intervals. Plots were established at Rathbun Reservoir in 1987, in Dallas and Webster counties in 1990, and in Jackson County in 1992 when RRD was found in these areas. Graft transmission was also studied in the greenhouse. In addition, investigators transported soil from field locations to the greenhouse; they planted a single multiflora rose seedling in each sample to test for RRD transmission via soil. They also examined the potential for transmission via seeds, dodder (a rootless, parasitic vine that establishes itself on a host and draws its food from it), and powdery mildew (which is often severe on infected plants). Investigators also tested whether therapeutic measures such as tetracycline and heat therapy caused remis­sion of RRD symptoms. Mite populations were monitored May through October of 1990 through 1992; data were collected both from solitary plants and from those growing in large, intermeshed clumps, in pure stands, or in association with other woody plants. Because infected plants are more susceptible than non-symptomatic plants to frost injury, investigators quantitatively determined stored starch and soluble sugars in both. In both field and greenhouse plants, stored starch reserves in the graft-recipient shoots decreased within three weeks after the infected grafts began growing until starch was depleted. Comparison of soluble sugars from multiflora rose plants showed a major de­crease in sucrose with corresponding increases in fructose and glucose in symptomatic plants. Electron microscopy revealed that healthy chloroplasts contained large starch granules; those from diseased plants were devoid of starch. Transmission electron microscopy was used to examine diseased plant tissue. Field trials: In 1993 field trials, two transects of ornamental roses were planted in each plot along the lines of prevailing Iowa winds. By recording data on development of mite popu­lation density and relative susceptibility of various hybrid roses, investigators could study how augmentation affected the spread of the disease to multiflora rose as well as the danger to hybrid roses. Volume 3 (1994) 34 Findings Field observations: Investigators character­ized three distinct disease stages for RRD by growth pattern, deformity, color, frost suscep­tibility, and flowering. Numbers of diseased plants increased rapidly for the first three years and then subsided as the supply of symptom­less plants was depleted. (Small plants usually die in two to three years; larger ones may survive four or five years.) Host range: All multiflora rose transplants in the field host-range plots developed symp­toms after six weeks. Investigators deter­mined that RRD host range is restricted to rose species; Prairie rose (Rosa setigera) appears to be immune. Several hybrid rose cultivars showed some symptoms. No rose-related plants developed RRD symptoms in the two years of observation, nor were any noted in surrounding vegetation, including the native roses, which are immune. In the greenhouse, no symptoms developed in any of the test plants other than rose, and several rose culti­vars appeared either fairly tolerant of or im­mune to RRD. Transmission to multiflora rose: Some grafts failed to transmit disease in the field because they lacked buds; others failed due to frost. Viable grafting was highest from the end of May through mid-July; it was also highest on current season growth. Transmission by graft­ing also failed in plants undergoing drought. Those plants contracting RRD via grafting developed stage-two (rosette) symptoms the following year. In greenhouse experiments, grafts lacking buds transmitted RRD as effectively as those with buds. Of 120 plants mechanically inoculated with sap, only two developed symptoms. Transmission of RRD via soil, seed, mildew, or dodder did not occur. Neither tetracycline treatment nor heat therapy prompted remission of symptoms. Production of new growth in graft-infected plants was strongly inhibited; this finding was consistent with observations of field-dug plants. Mite populations were low in 1990 and 1991 until mid-July; they peaked at the end of Au­gust. Investigators speculated that mite popu­lations increase during extended periods of high temperatures. Eriophyid mites may be transported by other arthropods (as well as by wind), particularly those biologically linked to the mite's preferred host. The reduced spread of RRD in heavily shaded areas suggests that RRD will not totally eliminate every stand of multiflora rose (see Fig. 1), and that in time, infestations will recur. Colonization of graft-inoculated plants by mites was earlier and most consistent on symptom­atic plants located in groups of large plants with intermeshing branches. Isolated plants had the lowest early-season incidence of, and erratic subsequent colonization by, the mite vector. The causal agent remains unknown. Investi­gators eliminated all possible disease-causing agents of RRD in multiflora rose except for viruses. Several ribonucleic acids have been consistently associated with symptomatic tis­sue, which supports the virus theory. The risk assessment plots indicate that RRD shows no tendency to move more than about 100 meters from the augmentation site. Al­though based on only one year of data, this finding may be significant because it suggests minimal likelihood of spread to ornamental rose plantings. Only three ornamental rose Fig. 1. Rate of occurrence of new infections of RRD in plots located in full sun and in shaded areas. Leopold Center Progress Reports 35 For more information contact A. Epstein, Plant Pathology, Iowa State University, Ames, Iowa, 50011, (515) 294-3807. plants have been documented in Iowa as lost to RRD since 1986. In summary, this project produced the data needed to identify optimal timing and sites to efficiently augment exist­ing RRD infections for effective biological control of multiflora rose. Implications Multiflora rose constitutes a major pest on noncultivated land. Biological control of this pest can reduce reliance on widespread, ex­pensive pesticides that have potentially sig­nificant deleterious effects on non-target plants, wildlife, and groundwater. These findings strongly suggest that RRD has excellent potential as a biological control for multiflora rose infestation. Although widely distributed, RRD in its natural state is sporadic and thus is unlikely to eliminate multiflora rose on any one parcel of land. Because the causal agent in RRD that is lethal to multiflora rose can be readily transmitted by grafting in the field, with proper placement it can cause rapid, local intensification of RRD that will eliminate up to 98% of a multiflora rose stand in five to six years. In addition, because the causal agent is endemic and local flora are either highly resistant or immune, problems resulting from its augmentation are unlikely. Investigators will continue to monitor this aspect as technology is transferred to land­owners. The augmentation approach can be applied regardless of terrain; the cost is less than $0.50 for materials plus two hours of labor per stand of multiflora rose Because the causal agent is not yet identified and characterized, investigators plan to con­tinue their monitoring surveys as well as risk assessment plots for at least three more years. Ultimately, augmentation of RRD as a bio­logical control may significantly improve the quality, productivity, and value of approxi­mately two million acres of Iowa land. Education and outreach: Both farmers and commercial rose producers have followed this research closely—landowners are eager to apply this system of control on land infested with multiflora rose; ornamental rose growers, on the other hand, have been concerned that their plantings may be damaged by the 1993 field trials in this project. Investigators have addressed these concerns by following ID ALS technical committee recommendations to re­lease RRD on a county-by-county basis, mak­ing no releases within one-half mile of known cultivated rose plantings without the owner's permission. Ultimately, elimination of RRD breeding areas would benefit ornamental roses as well. Investigators have also produced an informa­tional extension bulletin (ISU Pm-1532) and are organizing an international symposium (supported in part by a grant from a major rose producer). In addition to popular press cover­age, presentations, and displays at various conferences and statewide events, a number of technical publications on this work are com­pleted or in progress. Project investigators cooperated with other ISU plant pathologists, an entomologist, a botanist, a biochemist, ID ALS, the Iowa De­partment of Natural Resources, and private landowners. Commercial rose-producing nurs­eries have contributed nursery stock (for use in the risk assessment plots) as well as monetary support for the symposium. Communication is ongoing with scientists working on similar projects in other states. Volume 3 (1994) 36 

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Characterization of the Rose Rosette Disease causal agent: potential for biological control and multiflora rose

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