Friday, August 5, 2011

Rose Mosaic and Rose Rosette by Stephen Vann - August 2011

Rose mosaic and rose rosette are common diseases that occur wherever roses are grown. The microorganisms that cause these two diseases are easily spread through vegetative propagation by grafting or budding of infected material. Rose mosaic is often associated with mixed infections of prunus necrotic ring spot virus (PNRSV) and/or apple mosaic virus (ApMV). Rose mosaic is probably the most common viral disease of roses.
Rose rosette is believed to be caused by a virus or virus-like microorganism. This disease agent is thought to be spread by eriophyid mites that feed on the plant. It can also be spread through grafting. Rose rosette is a much more destructive disease than rose mosaic. Plants infected with this agent usually die rapidly, sometimes within one to two years. This disease is commonly found on wild roses (Rosa multiflora) that are grown in the Midwestern, Southern and Eastern United States. It is a major concern to the nursery industry and home gardener. It occasionally occurs in domestic rose plantings. Rose rosette can be spread from multiflora roses to cultivated roses.


Wavy white to yellow line patterns and ring spots on leaves are some of the symptoms of rose mosaic.
Rose mosaic produces a variety of symptoms on the leaves, including wavy white to yellow line patterns, ring spots, yellow net patterns and yellow vein banding. Symptoms of this viral disease vary considerably with the rose cultivar, time of year and environmental conditions in which the plants are being grown. Plants infected with this virus tend to be less vigorous, making them more susceptible to other plant stresses, such as cold injury. Cool temperatures tend to favor virus multiplication and disease development within the rose plant. Plants may not show symptoms for a year or two after planting. The overall effects of rose mosaic tend to be mostly from an aesthetic standpoint, causing an unappealing leaf appearance. There may be some reduction in flower production and loss of overall vigor, but this virus disease rarely kills the plant.
Rose rosette-infected plants exhibit a variety of symptoms on susceptible plants. Symptom expression may vary according to cultivar. The most obvious symptoms include rapid elongation of new shoots, witches’-broom (short internodes with clustering of small branches), conspicuous red coloration of branches and excessive thorn production on the branches. Flowers can be deformed and mottled. Flower buds may also become deformed and abort. Disease diagnosis is based primarily on characteristic symptom expression or by grafting suspect plant material onto known healthy material followed by symptom development over the course of weeks or months.
Prevention of these two rose diseases is accomplished primarily through growing and propagation of virus-free plant material. No pesticide can cure these or other viral diseases of ornamentals. Rose mosaic- or rose rosette-infected plants should not be used for propagation. Because the natural spread of rose mosaic is minimal, infected plants do not need to be removed unless growth becomes undesirable. With rose rosette, suspect plants should be removed and destroyed. Infected plants should be uprooted and burned if permitted. Wild roses, which may serve as reservoirs for infection, should be removed from the vicinity of cultivated roses.
(Photos by Stephen Vann.)

Stephen Vann, Ph.D, is an assistant professor and extension urban plant pathologist with the University of Arkansas, Division of Agriculture.

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