There’s hope that new USDA funding into research on Rose Rosette Disease (RRD), which is devastating rose plantings throughout much of the USA, will help find ways to halt or treat the disease.
Rose Rosette Disease is carried from rose to rose by a tiny eriophyid mite, Phyllocoptes fructiphilus. The mite lives in scales at the base of branches and/or inside partially opened buds; wherever the mites can find living (soft) tissue they will winter inside. Some rose experts believe it is also transmitted by bud grafting of infected stock and also under the ground by root-to-root grafting among closely spaced plants. Hot, dry weather encourages mite populations and increases the spread of the disease.
RRD itself is a virus which causes: ‘witch’s broom’ new growth; new red leaves that fail to change to green; some long, pliable but oddly-thick cane-like growth; mottled color on buds and flowers; excessive thorn production, and lack of winter hardiness.
The rose bush becomes progressively uglier and more misshapen, but the virus can also cause death of the whole plant after 2-3 years of infection. Even rose cultivars bred for overall better disease resistance like Knock Out Roses will be infected by, and die from, RRD.
RRD has already devastated the rose collections of Brooklyn Botanical Garden and the Scotts Arboretum.
The mite is endemic to the USA and probably evolved with native species, but its spread and disease transmission has been accelerated by unchecked weedy growth of Rosa multiflora, which is particularly susceptible to the disease. Rosa multiflora, from Japan, was originally introduced to the USA to form ‘living fences’ in rural areas through the Mid West but has now naturalized throughout the eastern and southern states. Other known host species include Rosa rugosa, Rosa canina and Rosa eglantaria. It’s possible that a wide-spread allied genus, Sorbus, might also host the mite.
“Garden roses, which form the cornerstone of the multi-billion dollar landscape industry, annually generate wholesale U.S. domestic bare root and container production valued at about $400 million. There is an urgent need to control rose rosette disease.”
said Dr. Dave Byrne, Texas A&M AgriLife Research horticulturist and lead scientist of the project. The $4.6 million research funding from the USDA will look at ways to manage, mitigate, and solve this destructive garden rose pathogen.
RRD has been known in the USA since the 1940s, but it’s only in the past few years that it has become a horticultural disease of such national importance. Although weedy Rosa multiflora is a principal vector, the popularity of mass-planted landscaping roses has also contributed, as these monocultures provide a much bigger habitat for the mite to become established in gardens and public landscapes.
In the following video, Jen Olsen, Assistant Extension Specialist at Oklahoma State University Plant Disease & Insect Laboratory, explains how you identify Rose Rosette Disease (RDD) and strategies for preventing plantings from falling victim to the mite vectored disease, and what to do when you first spot it.
RRD has been reported as far north as Canada. Some gardening forums in the UK suggest that it may now also be in the UK, but this is not confirmed and the symptoms of RRD are easily confused with those of herbicide damage.