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Rose Rosette Disease - A Follow-up

© Mark Whitelaw

Last July, I announced what has turned out to be the first confirmed case of Rose Rosette Disease in the north-central Texas area. Although the disease had been known in the wild R. multiflora stands in the eastern part of the state since 1990, it had never before been confirmed in a cultivated rose garden until this summer.

Since that first sighting and report, numerous occurrences of the disease have been popping up around the Dallas-Ft. Worth Metroplex area. One case of particular interest to my fellow community rosarians is the infection of 11 roses in the Ft. Worth Botanical Garden. The Gardens contains more than 1900 roses, and a highly infectious outbreak could wipe out most of them. Additional cases are suspected in the gardens of three other rosarians, and the disease appears to be spreading rapidly. Additional outbreaks of the disease have appeared in Denton and Collin counties just north of the DFW area. In one garden, a rosarian has lost not less than 10 of his roses.

Such a wide-spread outbreak in such a short amount of time prompted a meeting on September 1 with Dr. George L. Philley, Extension Plant Pathologist for Texas A & M University in Overton, Texas, and the central point of contact for monitoring the spread of Rose Rosette Disease in the state. Attending the meeting were Dottie Woodson, Agricultural Extension Service representative for the area, senior staff for the Ft. Worth Botanical Garden, and members of the Ft. Worth Rose Society, including myself.

Dr. Philley presented a briefing on the disease and the mite, Phyllocoptes fructiphilus, the suspected carrier of this disease. According to Dr. Philley, Rose Rosette is only one of four or five worldwide plant diseases that act like a viral disease, but cannot be detected even with the help of electron microscopy. Furthermore, there are no known cures for the disease. It is 100% deadly to the rose! And in a very short period of time!

P. fructiphilus can barely be detected with a strong hand lens. It is a very small member of the mite family - about 0.3 - 0.5 mm long, creamy white, with four distinctive legs at the front of its body. The remaining four legs, near the rear of the body, are rudimentary and appear as minute bumps.

This type of mite is called an "aerified mite" because it is easily dispersed through the air by "ballooning." That is, it can expel a minute filament of webbing silk, catch the wind, and travel for dozens, if not hundreds, of miles. It is also suspected of travelling piggy-back on aphids. The mite almost always appears in the new growth area of the rose (usually the top 7 - 10 inches of the stem), and almost always lives in the "bud eye" (the auxiliary bud that forms at the base of the petiole near the stipule).