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Rose Rosette

This disease of rose is believed to be caused by a viruslike pathogen. Unfortunately, the pathogen cannot be cultured in a laboratory, so diagnosis of this disease at the University of Illinois Plant Clinic is based on symptoms alone. Since symptoms are fairly distinct, the lab may not be needed except in cases of confirmation.

The new growth (leaves and stems) on infected plants is deep red. Leaves may show crinkling and distortion, or a mosaic pattern of green, yellows, and reds. An infected plant produces numerous lateral shoots that grow in different directions, giving the plant a witches' broom appearance. These shoots are typically deep red and much thicker than the canes from which they grew. Thorns on these stems are more abundant than normal. Overall, the plants have bright red, thick, thorny new growth. To anyone who has grown roses, this will not appear normal. The plants usually die within 22 months of infection.

Rose rosette is thought to be spread by the very tiny eriophyid mite. This mite cannot be seen without a microscope; 20 could fit on the head of a pin. Also of concern to growers is the fact that rose rosette can be spread by grafting.

Multiflora rose is the most common host of rose rosette, but cultivated flowering varieties can be affected as well. Climbers, hybrid teas, floribundas, miniatures, and a number of "old fashioned" roses have been reported as hosts.

Infected plants should be removed as soon as rose rosette is identified or confirmed. Dig up and remove all plant parts, including roots. This material should not be used in a compost pile. Plant multiflora roses and garden roses as far apart as possible. Controlling rose rosette through mite control has not been shown to work with any consistency. Research suggests that the critical mite transmission occurs in May and June, so if you decide to use miticides, concentrate your efforts in those months next year. For more about rose rosette, consult Report on Plant Diseases No. 666.

Author: Nancy Pataky


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