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How long does it take to show symptoms?

We don't know. We also don't know when a rose was bitten by the mite that carried the pathogen to that rose. We have seen healthy roses moved into a garden with high disease pressure, and they showed RRD symptoms in two weeks. We assume that an RRD infected mite fed on the rose very soon after it was planted.  Most of the long time spans listed below were for graft transmissions.  That is of no value to rose growers because our roses are infected by mite transmission.  The data from Dr. Amrine, below, for carefully monitered  mite transmission is germane and his reported 17 to 24 days from infection to show symptomsit agrees with what we have seen in gardens. Recent rains may magnify symptom expression. If a rose is infected in late fall as it enters dormancy, RRD will emerge with spring growth.

For mite or graft pathogen transmission, the time period from infection to showing symptoms ranges from three weeks up to one year according to Texas A&M.  In Spring of 2002, newly potted up roses were moved to a home improvement center in Knoxville for a May 1 opening.  By June 15 ten of the unsold roses were showing many RRD symptoms;  RRD exists in numerous Rosa multiflora upwind of that garden center. (When aprised of the problem, the garden center destroyed the sick roses.)        
Amrine et al. (1988:p 239) tested transmission rates for RRD by both grafting and mite transmission. Their paper details methods and results. "Graft transmission of the RRD agent to rooted cuttings of Rosa multiflora required 45 to 80 days and was only 46% successful. Graft trasmission  to large vigorously growing transplants was more rapid (30-60 days) and 100% successful.  .. Laboratory transmission of RRD by the eriophyid mite, Phyllocoptes fructiphilus (Acari: Eriophyidae) to transplants in 1986 was 92.3% and symptoms appeared in 17-24 days. ......In 1987 the rate of field transmission with P. fructiphilus was 12.5% and lab transmission was 20% with symptoms appearing in 30-279 days.  Reduced laboratory transmission in 1987 was thought to be drought-induced."

This brings up one more point. How quickly can a mite infect a bush?  Infection is when the plant acquires the pathogen.  By the time a plant shows symptoms, it's been sick for a while. There are no studies of the accession time of RRD. (Studies of a similar mite spread disease on peaches show transmission in as little as 15 minutes and increasing with time on plant. We do not know if this applies to RRD or not.)
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