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A new fact sheet has been posted on rose rosette disease (RRD) caused by the rose rosette virus, specific to rose species. 2/10/2015
Description and Geographic Distribution
ROSE ROSETTE DISEASE (RRD) is specific to Rosa species and is caused by the rose rosette virus, which is carried by a very small eriophyid mite, or graft transmitted. The virus disease is a threat to all cultivated roses, even rose cultivars with some disease resistance to black spot, such as the Knockout Series. Symptoms include abnormal and persistent red coloration of shoots, accompanied by shortened internodes and distortion, distorted flower buds or lack of buds, extreme thorniness (but softer thorns), and decline. RRD was first found in the Western U.S. in the 1940’s, and has been observed for over ten years on
multiflora rose in the Delaware, Maryland, and Pennsylvania region. RRD can be difficult to diagnose, but the presence of the eriophyid mite in the leaf axils and buds was a sign used to confirm the disease. Symptoms of herbicide injury and powdery mildew may look similar and be confused with RRD. The virus is carried by the wingless, sausage-shaped eriophyid mite, Phyllocoptes fructiphylus, active from May through October, and easily carried on air currents. The eriophyid mite is too small to be seen with a hand leans. The virus may also be transmitted through grafts. Once introduced into a plant, it may take weeks or months for symptoms to develop. Pruning may remove virus infected tissue, but over time the entire plant may become infected down to the roots. It is believed that the spread of invasive multiflora rose resulted in widespread distribution of rose rosette virus.
RRD Disease Management is best accomplished by avoiding the disease, but that may not always be possible. It is best to purchase clean stock from reputable sources, and eradicate multiflora from adjacent landscapes if possible. Allow good spacing between rose plants. Keep roses in good vigor by regular pruning and fertilization. If RRD is detected (lab confirmation may be necessary), trim plants immediately. If symptoms persist on new growth after pruning, remove the plant and do not compost or chip nearby. Eriophyid mites are difficult to control with chemicals, products labeled for spider mites will not control, and chemicals will also kill beneficial predatory mites. Insecticidal soap, kaolin clay, or neem oil may have some effect on populations of eriophyid mites. Work is in progress on breeding for resistance to rose rosette virus in rose cultivars.
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