Virus hits both invasive, ornamental roses
If you spend time outdoors in Butler County, you may be familiar with multiflora rose, an aggressive, invasive plant.
Multiflora rose (Rosa multiflora) was introduced into the United States from Japan in 1866 for use as rootstock for grafting ornamental roses.
In the 1940s, multiflora rose was used as a conservation “tool” because of its ability to grow rapidly and almost anywhere, including strip mines to prevent erosion. It has also been used as a living fence to enclose livestock and provide food and shelter for wildlife.
Hundreds to thousands of nutritious fruit (hips) are developed on each plant, and each hip produces an average of seven seeds. The seeds are capable of germination for at least 20 years.
In many locations multiflora rose now dominates the landscape as dense, thorny thickets along roadsides, pastures, and in old fields. Its eradication is nearly impossible, requiring a combination of mowing and herbicide applications.
As a result of its invasive nature, multiflora rose is listed as a “Class B” noxious weed in by the state of Pennsylvania.
Some landowners have been encouraged to find that multiflora rose is highly susceptible to rose rosette disease, which has been present for many years in wild roses.
Rose rosette disease is caused by a virus (Emaravirus sp.) carried by a tiny mite (Phyllocoptes fructiphylus). The mite is wingless and moves on air currents, or is transported on clothing and equipment.
They feed and reproduce on the tips of new growth. Young mites can reach maturity within a week depending on temperatures, and multiple generations are produced each year.
The virus carried by the mite causes a red coloration on the underside of leaf veins and a rapid increase in growth resulting in clusters of many short, reddish shoots that create “witches' broom” formations and excessive growth of thorns along stems.
Leaves become deformed, crinkled and discolored while branches and shoots die back. The virus is most easily transmitted from May through mid-July during the active period of plant growth.
Plants become extremely susceptible to freeze damage and other diseases such as downy mildew and black spot. Small plants can die within two years while larger plants may survive five years.While all of this is cause for some celebration among those trying to control multiflora rose, there is concern among rose growers because multiflora rose acts as a host for the virus.The virus can be spread downwind to ornamental roses, and there are no effective treatments for rose rosette disease if found on ornamental roses. Ornamental rose breeders have been working to develop disease resistant cultivars; however, no ornamental rose is completely resistant to rose rosette disease. Gardeners, landscape managers and homeowners who grow ornamental roses should be vigilant for symptoms of the virus.Here are a few interventions to protect ornamental roses from rose rosette disease:Prune roses in late winter or spring. Mites overwinter in flower buds or seed heads. Removing the buds or seed heads can eliminate mites.Do not use leaf blowers around roses; mites can be transported on air currents and can be spread inadvertently.Site roses in a sheltered location that protects them from prevailing winds.Maintain space between rose bushes to reduce the likelihood of mites crawling from one plant to another.If symptoms such as those described above are seen on ornamental roses, the entire plant, including the roots, should be removed and destroyed by burning or bagged for disposal.Spreading mites may occur during disposal. It is recommended to place a bag over the entire plant before removal to limit the possibility of spreading the mites that carry the virus.Cut the plant at ground level and dig out the root system separately. Leaving the roots in the soil can keep the virus alive.After the plant is removed, clean tools and clothing before doing any other gardening.If you have questions about rose rosette disease, call the Master Gardener Garden Hotline at 724-287-4761, Ext. 7, or email the Master Gardeners at butlermg@psu.edu.Master Gardeners and Extension educators from across the state answer questions during “Garden Hotline LIVE.” Visit the Penn State Extension Master Gardener group page: www.facebook.com/groups/696217890434068.<em>Mary Alice Koeneke is a Penn State Master Gardener of Butler County.</em>
