New Test Confirms Rose Rosette Disease By Will Rowlands pleting the sequencing of the genome is Wichurana ...” of the virus should help in this regard. David Austin Roses USA told us hen we heard that Rose Knock Out® Roses and Drift® Roses, “... as far as we know all rose varieties Rosette Disease (RRD) for example, are susceptible but www. from whatever group are equally had been confirmed in W starrosesandplants.com reports that susceptible to RRD.” Connecticut by a newly developed quick removal of infected plants (rogue- Clearly there’s a difference of opin- molecular test, we decided it was some- ing) is sufficient to stop the disease. ion. Part of problem is that we’re not thing our readers should know about. always on the same page. After all, most people have a rose or Some native roses reportedly have two on their property. some resistance to the virus but not the I figured it would be a straight- mite. If this is the case, they may harbor forward research project but I was the mites that vector the disease but wrong. Even though the disease has won’t die or exhibit symptoms. been known for 75 years, we really Most ornamental roses, on the other don’t know all that much about it. hand, appear susceptible to the virus And, to complicate matters, the experts to some degree. don’t always agree on some points. The home gardener needs more The Basics information on the susceptibility of RRD, also known as witches’-broom popular roses to the mite and the virus. of rose, is caused by a recently identified Infected plants typically die in 1 to virus. There’s general agreement that the 5 years, depending on the plant’s health virus is spread by microscopic eriophyid and size. There is no cure once the virus mites (Phyllocoptes fructiphilus). takes hold and become systemic. Un- Although they only have four legs, fortunately, RRD also makes the plant Photo / James W Amrine Jr, eriophyid mites are actually Arachnids University of Kentucky, Bugwood.org more susceptible to other diseases. or, to be more specific, they’re members Diseased stem on left exhibiting an It’s worth noting that some plants of the Acari or Acarina taxon. enlarged thorny stem. Normal stem may become stunted or symptomatic Gardeners probably know them and flower on right for comparison. in some way but won’t die in a timely best as gall mites or rust mites. ere manner. They may hang on and remain are hundreds of species and many that capable of infecting other plants. haven’t even been described yet. Not Research surprising when you consider they’re It’s a serious enough problem that not visible to the naked eye. the USDA announced a $4.6 million e virus and the mites are both five-year grant to combat RRD. e assumed to be native to North America funds will reportedly be matched by but the proliferation of Rosa multi- in-kind and cash contributions from flora is usually credited with having industry breeders and growers. facilitated their spread across North America. Lookalikes Multiflora rose is highly susceptible Some of the symptoms of RRD to the disease/mite and, therefore, serves resemble herbicide damage so con- as a reservoir of both the inoculum firmation by PCR (polymerase chain and the vector. Photo / Mary Ann Hansen, Virginia Poly- reaction) testing of the DNA or identi- technic Institute & State Univ., Bugwood.org fication of the mites under a micro- The disease is often said to affect Discoloration caused by RRD. all species and cultivars in the genus scope is sometimes necessary, although Rosa, including cultivated varieties. Flower Carpet® Roses, we’re told, the disease can oen be diagnosed Susceptibility may vary, however, and have been minimally impacted. symptomatically. some experts believe roses with an “In discussions with Reinhard Noack, Background Asian heritage may be more susceptible. the Flower Carpet breeder relative to Symptoms consistent with RRD have R. multiflora is native to Japan, Korea the disease,” said Judie Evrard Brower been described as far back as the early and Eastern China. of Tesselaar USA, “he believes the rea- 1940s in Northern California, Wyoming There have been some anecdotal son we are seeing a lesser incidence of and Manitoba. The popular wisdom reports of wild roses with resistance RRD on Flower Carpet is that a lot of is that the disease and mites are native but more work needs to be done. Com- the breeding stock for Flower Carpet May/June 2015 1 Connecticut Gardener to North America but its proliferation Multiflora roses are so susceptible diagnosing the disease symptomatically was facilitated by the widespread use to the disease that it has been suggested ever since. According to Sharon Dou- of multiflora rose. that the mites can be used as a bio- glas, head of the Dept. of Plant Path- R. multiflora was imported from control. Rose aficionados, however, ology & Ecology, they’ve been using Japan for rootstock and other uses are not sold on this approach. phrases such as “consistent with symp- as early as the 1700s but went “viral” Donna Ellis, chairman of the toms associated with RRD.” in the mid-1900s. Connecticut Invasive Plant Working “In 2011, the causal organism was Over the years, multiflora rose has Group put it this way, “A goal of bio- determined to be a virus – a member been used as wildlife habitat, food for logical control is to find the most of a new group of viruses called Emara- songbirds, for erosion control and recla- specific bioagents with the least non- virus,” said Douglas. “There is still some mation projects, as a living fence and target impacts.” controversy about this, and whether it even as a crash barrier and headlight Ultimately, over the course of might be more than one virus.” glare blocker on highways. decades, RRD may take care of Knowing the causal organism Unfortunately, the plant is a prolific Rosa multiflora on its own. allowed researchers to develop a seed producer that can also spread by molecular test for the virus. Connect- RRD in Connecticut layering (canes touching the ground icut samples were sent to a National In 2009, Marci Martin, then the put down roots and develop into new Plant Diagnostic Network lab at rosarian at Elizabeth Park in West Hart- plants) and is considered invasive in Oklahoma State University and the ford, brought samples to The Connecti- many states, including Connecticut. disease was confirmed in October 2014. cut Agricultural Experiment Station Birds and other animals assist by eating CAES is getting ready to do the test- (CAES) in Windsor. Under a dissecting the hips and distributing the seeds. ing. They’re just waiting for the testing microscope, Rich Cowles and Jim Interestingly, having multiflora protocol to be finalized. LaMondia found the tiny eriophyid rootstock does not appear to increase mites that spread the disease deep Disease Transmission a plant’s susceptibility to RRD which within a growing tip. The disease is transmitted by the may have more to do with the angle The mites are three or four times mites or by grafting. The mites acquire of the cane/petiole junction. The over- smaller than spider mites and cannot the virus by feeding on infected plants. wintering female mites appear to prefer be seen without magnification. Good hygiene is recommended. a tight angle. The Experiment Station has been While sap does not appear to transmit the virus, the mites can be transported on dirty tools, although it doesn’t appear they live very long without a host. “The tiny mites carry the Rose Rosette Virus in their mouthparts and impart it into the vascular system of the plant while feeding,” says Martin, a Master Rosarian and former president of the Connecticut Rose Society. Mite Movement The mites are wingless but can crawl from plant to plant. They’re so small and light they can be carried long dis- tances on wind currents, sometimes called ballooning. For this reason, it has been suggested that taller roses may be more susceptible. Unfortunately, the mites can also be transported on clothing, tools and possibly by phoresy (attaching them- selves to larger critters). Prevention Scout your location and, if possible, remove all multiflora rose within 100 meters. This may take some vigilance as it’s a prolific seed producer and continued on next page Connecticut Gardener 2 May/June 2015 rest of the rose looks good, I’ll leave the Rose Rosette Disease — continued from page 13 rose and wait and watch . and hope that the virus has not gone systemic.” the seeds can remain viable in the soil • Lateral buds produce unusual This is a 50-50 proposition. Remem- for 10-20 years. If you can’t remove it, looking shoots ber, recently infected canes may not at least try to avoid planting your roses • Abnormal flower color show symptoms for weeks or even downwind from them. • Lack of winter hardiness months. Avoid overlapping leaves and canes. • Spiral cane growth It’s basically a numbers game or Proper spacing between plants makes • Cultivated roses may exhibit thick, risk/reward decision. If you have one it more difficult for the mites to crawl succulent stems and excessive thorn- plant that appears infected and have from plant to plant. The mites hang iness. (Some varieties have a lot of a ton of ornamental roses, you should out on the undersides of leaves and prickles naturally.) probably just remove the plant(s). in growing tips. Females overwinter • Symptoms on cultivated roses are When removing plants you need to in the canes and move to new shoots typically less severe get everything, including the roots, to in the spring to lay their eggs.