The scourge of multiflora roses

June 28, 2012 

Rosa multiflora,

COURTESY OF EAST TENNESSEE STATE UNIVERSITY

My friend Hank Stallworth spent summers at his grandfather’s farm, Singleton, in Calhoun County.

Walking down the railroad track was a popular pastime until one day the train caught him with nary a place to escape except a huge hedge of multiflora rose. His grandfather felt there was no need for a whipping; that fool-hardy boy was punished enough by the thorns on those sturdy canes.

Rosa multiflora, a native of Japan and China, was brought into the United States on purpose. In the late 1880s, it was used as a rootstock to confer disease resistance to more attractive roses. In the 1930s it was highly promoted and planted as a wildlife food and a living fence – cattle could browse on new leaves and birds and other animals consumed the hips. Those colorful fall fruits from a single plant can produce a million seeds which are then carried long distances by the animals who eat them.

This rose species has an Achilles’ heel; the rose rosette virus. This condition first manifests itself as red or pink coloration in leaves; not a very helpful diagnostic clue.

But in infested plants, the color does not fade as the leaves mature. Other symptoms include elongated shoots, clustering shoots (witches’ brooms) or excessive thorniness. Leaves are distorted and can’t produce sufficient food. Buds wither or abort. In a short time, from one to five years, the plant dies.

Wouldn’t it be lovely if we could get rid of this invasive species by helping the tiny eriophyid mites who spread this virus cover more ground? Multiflora roses that grow in shade generally escape infestation, but their seeds are quickly carried to sunnier spots where they sprout to serve as new sources of infection. These wingless, two-legged mites can be carried by winds onto other susceptible rose varieties – almost all the rugosas, hybrid teas, floribundas, and even our new landscape default selection – the Knock Out roses. The same symptoms described above develop and gardeners must be diligent in scouting for them if they have rose beds. As soon as you recognize that a plant is infested, you should remove it and destroy it by burning (if allowed) or bagging it and sending it to the landfill.

Do not let the stems of plants touch each other; that provides a handy highway for the mites. Dig diseased plants out carefully so no infested root stock is left to resprout. You can replant in areas where plants were removed if you were careful to leave no root tissues as this is not a soil-borne disease.

If you grow roses in rural areas where multiflora roses are abundant, your prized specimens usually escape infestation if they are planted at least 300 feet from any of those introduced individuals. The size and density of stands of multifloras make herbicide control difficult but for serious rosarians an initial and continuing cleanup of surrounding land under their ownership would provide protection.

Researchers suggest that with cultural practices in place, a miticide that controls both eriophyid and spider mites can prevent some infestation. (For more information, search “Rose Disease Clemson HGIC.”) Spray plants growing near any that were diseased and removed. Sprays should be applied every two weeks from late spring through the summer. This new disease will test the mettle of rosarians who must be even more diligent to protect those perfect buds.

Zinnias anyone?

Amanda McNulty is an associate extension agent for the Clemson University Cooperative Extension Service and will be the new host of “Making It Grow” broadcast weekly on ETV television stations. Website: www.clemson.edu/extension/hgic/

Awards for Amanda McNulty

Local gardening columnist Amanda McNulty has received two honors with the Garden Writers Association in its annual contest. Two of her columns published in The State – "Fatty, Fatty, two by four" and "The Skinny on Trees in Drought" – received first and second place silver awards of achievement, respectively, in the newspaper writing category. Her columns are eligible for the writers association’s Gold Awards, which will be announced at the annual banquet Oct. 15.

The State is pleased to provide this opportunity to share information, experiences and observations about what's in the news. Some of the comments may be reprinted elsewhere in the site or in the newspaper. We encourage lively, open debate on the issues of the day, and ask that you refrain from profanity, hate speech, personal comments and remarks that are off point. Thank you for taking the time to offer your thoughts.

Commenting FAQs | Terms of Service