Rose Rosette
Click for larger image Witches'-broom caused by rose rosette on a shrub rose (Rosa 'Baiore' POLAR JOY)

Rose rosette disease, also known as witches’-broom of rose, is a virus or virus-like disease, such as a phytoplasm, that is spread by a very small, eriophyid mite. The disease is limited to plants in the genus Rosa. Its main host is the multiflora rose, which is considered a noxious weed throughout much of the United States. Interest in rose rosette has been generated by the threat to garden roses and its possible use as a biocontrol for multiflora rose.

Symptoms and Diagnosis

The earliest symptoms of rose rosette disease include a red pigmentation of the underside of leaf veins followed by sharply increased growth of vegetative shoots, which are typically more succulent than normal and colored in various shades of red. Leaves will become deformed, crinkled, and brittle with yellow mosaics and red pigmentation. As the disease progresses, leaves become very small, petioles are shortened, and most lateral buds grow, producing short, intensely red shoots. The disease causes the plant to be exceptionally susceptible to freeze damage. Symptoms on cultivated roses are typically less severe than on multiflora rose. Cultivated roses show symptoms of thickened, succulent stems and a proliferation of thorns.

Life Cycle

The disease can be transmitted by grafting and by an eriophyid mite, a wingless mite that can travel passively in the wind. Transmission typically occurs between the months of May through mid-July. Symptoms from new infections usually start appearing in mid-July. In general, smaller plants go through the disease stages more quickly than larger plants. Small plants are usually killed in about 2 years, while a large plant may survive for five years in a deteriorated condition.

Integrated Pest Management Strategies

1. Remove ornamental roses with symptoms. The entire plant including the rootstock should be removed and destroyed.

2. Plant ornamental roses as far away as possible from known stands of multiflora rose.

3. Control the disease by controlling the mite. Pesticides such as carbaryl (Sevin), bifenthrin, horticultural oils and insecticidal soap may provide some protection when applied at weekly intervals during the months of June and July.

4. Using rose rosette disease as an IPM strategy: The multiflora rose is an exotic invasive species that is responsible for the degradation of millions of acres of farmland and recreational areas. Using the disease to control this invasive weed can cut costs and be considered environmentally friendly for reducing the amount of synthetic chemicals used. However, the disease also affects cultivated roses. One should be extremely cautious and good neighbor-minded when it comes to rose rosette disease.

Organic Strategies

Strategies 1 and 2 are strictly organic approaches. Of the insecticides mentioned in Strategy 3, consult the Organic Materials Review Institute (OMRI™) for appropriate products.

More images:

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Tell-tale witches'-broom caused by rose rosette on a shrub rose (Rosa 'Baiore' POLAR JOY)
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Witches'-broom of rose rosette on rose (Rosa)
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Do not confuse normal reddish growth on rose (Rosa) with reddish but excessively thorny growth caused by rose rosette
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Rose rosette on rose (Rosa)
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Witches'-broom on rose (Rosa) caused by rose rosette
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Symptomatic thorns on rose (Rosa) caused by rose rosette
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Left side of rose (Rosa) plant affected by rose rosette, right side still normal
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Rose rosette on rose (Rosa)
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Rose rosette on rose (Rosa)
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Rose rosette on rose (Rosa)
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