Sunday, April 12, 2009

Landscape - Rose Rosette Disease

The following is information on Rose Rosette disease which is thought to be a virus transmitted by the eriophyid mite.

Symptoms of rose rosette disease vary, but some of the more recognizable symptoms include rapid elongation of new shoots and witches' broom on small branches. Leaves are small, distorted, and may have a conspicuous red pigmentation. The red pigmentation is not a consistent symptom. Canes can develop excessive growth of unusually soft and pliable red or green thorns which may stiffen later. This excessive thorniness on the stems is diagnostic for rose rosette disease. Flowers may be distorted with fewer petals than normal, and flower color may be abnormal. Diseased plants may not exhibit all of these symptoms, especially in the early stages of the disease, so diagnosis can be difficult. The red pigmentation may be subtle and hard to distinguish from the normal reddish tinge of new leaves in spring. Monitor roses closely for symptoms to catch this disease as early as possible to help prevent its spread to nearby plants.

Control: Once a plant is infected there is no cure. The plant will die over the next 2 – 4 years. Plants that are showing all of the symptoms should be destroyed immediately. Some people try to control the eriophyid mite that spreads the disease. This involves applying Avid to the foliage every two weeks from May through October. This is obviously a lot of spraying. Forbid does have eriophyid mites on the label. It should provide control for at least 2- 3 weeks. You might be able to extend the spray intervals.

Rose rosette disease symptoms on leaves. Photo by James W. Amrine Jr., West Virginia University,

Information from the April 10, 2009 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension.

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