So far I’ve devoted this blog to beautiful things in the garden, such as heritage roses and trellised arches covered in rambling blossoms. Today, however, we take a turn for the ugly to discuss a particularly virulent rose disease called Rose Rosette. To this not-so-scientifically-minded gardener the Rose Rosette Virus (RRV) reads like something out of a sci-fi novel: An otherwise healthy plant contracts a mysterious, airborne illness which corrupts its RNA, causing it to mutate into a prickly, discolored mass of grotesque foliage resembling a witch’s broom. The plant then develops a taste for flesh, devouring unsuspecting small children and pets.
Ok, I may have made up that last part, but the rest is basically true. Since it was first documented in Manitoba in the 1940s, Rose Rosette has spread steadily throughout North America. Microscopic eriophyid mites act as the disease’s vector, spreading the virus from plant to plant (Byrne et al., 2018). After a mite feasts on an infected rose it hitches a ride on a gust of wind (or a careless gardener’s gloves) to find its next victim. Once infected, a rose plant will display some combination–but not necessarily all—of the following symptoms: reddening of foliage, excessive thorniness, flattening or fasciation of stems (see “devil’s tongue”), and development of bushy, broom-like masses of distorted flower buds (Windham et al., 2014). I would also add, based on my observations at Elizabeth Park, that in its early stages the foliage often bears an uncanny resemblance to frisée salad greens (though I wouldn’t recommend serving it at your next dinner party). RRV is fatal, with most plants succumbing to the disease within 3-4 years (Windham et al., 2014).
There is presently no cure for RRV, and no rose cultivars are immune, though new hybrids such as ‘Stormy Weather’ have shown promise (Di Bello et al., 2018), and some species display better resistance than others (Windham et al., 2014). That said, gardeners can take several precautions to prevent the spread of Rose Rosette. Plants showing symptoms should be dug up, bagged onsite, and immediately placed in the trash. Other intuitive, though not-yet-proven, preventative measures include regularly cleaning tools, pruning plants in early spring before over-wintered mites have hatched, and spraying plants with miticides.
Here at Elizabeth Park, RRV is far from reaching epidemic proportions, though I have had to remove several plants this year. Perhaps most tragically, I recently found a lone infected branch on the very same old glauca specimen I profiled earlier in this blog. Rather than dig that one up, I removed the affected limb and am currently practicing the waiting and praying method. Sufficient trials have not yet been conducted to determine whether pruning at initial observation is an effective strategy for treating RRV (Windham et al.. 2014).
For help in identifying Rose Rosette on your plants, see some photos I recently took of the disease here at Elizabeth Park.
Byrne, D. H., Klein, P., Yan, M., Young, E., Lau, J., Ong, K., … & Novick, D. (2018). Challenges of Breeding Rose Rosette–resistant Roses. HortScience, 53(5), 604-608.
Di Bello, P. L., Thekke‐Veetil, T., Druciarek, T., & Tzanetakis, I. E. (2018). Transmission attributes and resistance to rose rosette virus. Plant pathology, 67(2), 499-504.
Windham, M., Windham, A., Hale, F., 2014. Observations on Rose Rosette Disease.