ROSE ROSETTE

Also known as 'Witches' Broom'. This deadly affliction is 100 percent fatal. So if you see it, just dig up the plant and remove it from the garden as soon as possible, as the mites which spread the infection are present in the plant. There is NO cure for Rose Rosette. This affliction has three stages. The first stage is rapid, vigorous growth characterized by unusually dense formation of prickles on stems and canes. Canes appear overly large and purple or deep red in color. New leaves appear distorted and crinkled, often purple or deep red. The leaf stems may appear flattened and look almost like leaves. The second stage is the development of lateral growth having closely spaced internodes leaf buds. When leaf buds open, they become distorted or even fail to fully open, giving an appearance of rosettes. The third stage is characterized by spindly, chlorotic stem growth. Roses may show symptoms in as little as 3 weeks after infection, or they can have an incubation period of up to a year or more.

The symptoms of this affliction are described as 'virus like', because the exact actual organism which causes Rose Rosette has not actually been identified as of yet. The disease agent of Rose Rosette is transmitted from plant to plant by a tiny microscopic sized, wooly mite called Phyllocoptes fructiphilus. This is a type of mite called an eriophyid mite. This is NOT like a spider mite.

Hybrid Teas are less likely to be used as hosts by this mite. Heavily pruned roses seem to have the fewest problems. This disease was first detected in the 1930s in wild roses growing in the mountains of California and Wyoming. Then it spread to stands of Rosa multiflora, an almost perfect host, and moved across the country and into the Midwest. In the late 1970s and early 1980s, it swept like a wildfire up the Ohio River valley and into West Virginia. Today, it’s endemic wherever wild multiflora roses are found This viral infection is most common now in the Midwest where Rosa multiflora hedges are frequently planted and become infected.

Treatment: Just remove the infected rose and burn or destroy it. Same with the soil around it where the mites might overwinter. Prevention is possible by controlling mites, as this is how the virus is transmitted to the rose. But you should realize that miticides and other measures commonly used for treating spider mite infestations aren’t effective because this is a different type of mite. If it is a big problem in your garden you might want to keep hybrids of Rosa multiflora out of your garden. Many budded or grafted roses are on Rosa multiflora root stock, which needlessly worries some gardeners. Although Rosa multiflora is a host for the disease and for the eriophyid mite, a rose on multiflora roots is no more susceptible to rose rosette than it would be if it were on its own roots or on another type of root stock. It is apparently the top growth and specifically the petiole-cane junction that determines susceptibility. This affliction is NOT spread by pruners or by any other known agent besides the tiny mites. So it is not contagious in that way.

ACKNOWLEDGEMENTS: I would like to thank the following plant pathologists with the California Department of Food and Agriculture's Plant Pests Diagnostic Center: Dan Opgenorth and Dennis Mayhew. All the above information and pictures on these disease pages were taken by Baldo Villegas.

I would also like to include two more great sites on this deadly virus:

http://www.ext.vt.edu/pubs/plantdiseasefs/450-620/450-620.html

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