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Rose Rosette Disease – Friend or Foe?Back in late April, I received a phone call from a retired Penn State colleague and avid rose grower (rosarian). She was concerned that an heirloom or species rose might have rose rosette disease (RRD), a suspected virus that is spread by an eriophyid mite to certain susceptible roses. The eriophyid mite (Phyllocoptes fructiplilus) inhabits the shoot tips and leaf petal bases of roses and introduces the causal agent of RRD into rose as it feeds. This 4-legged mite is only about 200 microns long and 50 microns wide – small enough so that 20 could lie side-by-side on a pinhead. After examining the suspect plant and contacting several experts, we indeed believe that her rose is infected with the disease (see image 1). She has since cut back the infected rose hoping that infected canes have not spread the disease throughout the plant or moved to any of her other numerous roses. Obviously, the ornamental rose industry and rosarians are greatly concerned about this disease. There is really no practical way to prevent or manage RRD in susceptible contemporary or heirloom roses.
Image 1. Suspected rose rosette disease on a heritage species rose. This recent incident alone makes this article worth writing, but there is still more. RRD is a fatal disease of multiflora rose (Rosa multiflora), the much-despised noxious weed in many states including Pennsylvania. Multiflora rose is the dominant host for this disease, so RRD is most common in areas where multiflora rose thrive. RRD is commonplace in W. Virginia and in parts of the Midwest and scattered throughout numerous other states including Pennsylvania. It has been identified as far North as Harrisburg in Pennsylvania. Farmers and land managers plagued with multiflora rose have happily anticipated the arrival of RRD in the hope that it will reduce or even eliminate multiflora rose. After this heirloom rose RRD incident, I was more on the look out for symptoms of RRD on multiflora rose. RRD had not been reported in the State College area although we believed it was simply a matter of time. Mid to late May and early June are good times to see RRD symptoms on infected multiflora rose. The new leaves emerge with a brighter red to dark red mosaic pattern (Image 2). The pattern follows the leaf veins or may appear as spots and blotches. A proliferation of shoots often produces a “witches broom” symptom. Other symptoms include rapid stem elongation, breaking of axillary buds, which results in numerous red lateral shoots and thick bunchy clusters of wrinkled, reddish-green leaves, which are distorted and reduced in size.
Image 2. Rose rosette disease on multiflora rose. To make a somewhat longer story shorter, the result of my heightened awareness was the identification of RRD on multiflora rose in the State College area. Specifically, we identified what we believe to be RRD on multiflora rose in a number of pastures near the Penn State campus. We are still formulating what if any thing should be done. Do we celebrate, now that RRD may finally help control the local multiflora rose problem? Do we quickly mobilize an assault team to eradicate infected roses to stop the spread of the disease to nearby susceptible ornamental roses? A chief recommendation for rose growers is to remove multiflora rose in neighboring areas since it is the primary host for the disease. However, the mite can be airborne and travel several miles, then descend randomly and infect susceptible roses. Perhaps you see the dilemma?? Maybe rosarians, farmers, and land managers really want the same thing? The obvious solution might be to initiate an intensive multiflora rose management campaign to reduce the host range, which would ultimately reduce the vector (mite), and thus the disease. However, since multiflora rose is so widespread, this would require a great deal of effort and $$. At least, reducing multiflora rose populations in urban environments or where it is in proximity to ornamental rose growing locations could be a start. So where are we? At this point, we hope to get a better handle on the incidence of RRD infected plants locally. We hope to initiate research to help answer how quickly it spreads and whether the distribution of the disease follows a pattern. According to the literature, RRD symptoms first appear 17 to 90 days or more after infection on healthy multiflora rose. The majority of new infections appear in July and August. About 10 to 15% of infected plants show a loss of symptoms for one or more months, but the symptoms later reappear. The entire multiflora rose plant including the root system dies an average of 22 months after first becoming infected. On contemporary garden roses, the symptoms are usually less severe, but the disease also kills some cultivars. On some cultivars, the symptoms appear transient and the plants recover, while other plants weakened by RRD, die from other causes. Garden Party, Mister Lincoln, Chicago Peace, Gold Medal, Olympiad, Pink Peace, Sun Flare, French Lace, Graham Thomas, Othello, and Red Meidiland are some of the improved cultivars documented to be very susceptible to RRD. Old, heirloom, and species roses probably vary in susceptibility to the disease, but little information is known. In closing, as this problem/solution develops, we’ll try to keep you informed. (The article was written with the help of several references including Rose Rosette Disease, 1999 Report on Plant Disease No. 666, University of Illinois and the American Rose Rambler #39, 2001.)
W. S. Curran, wsc2@psu.edu Weed Science, Crop and Soil Sciences |
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