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 oen 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

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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. The symptoms of the disease can be sure. Bag everything in situ, carefully, You can also try alternating different vary with species, cultivar and age of the and remove. Do not compost! rose varieties or even alternating roses plant and may be due to other causes. Most experts say the soil itself is not with other plants to make it more diffi- Glyphosate damage, for example, infected but you need to get everything cult for the disease to spread. causes some of the symptoms associated because the mites can overwinter in Give your ornamental roses a good with RRD. It appears to cause similar plant and root fragments. prune in late winter before new growth deformities but not the vigorous growth Do not replant the area with roses appears. Focus on the upper regions and thorniness. 2,4-D damage can unless you get all of the roots and any where the mites are more likely to be include leaf and flower distortions. volunteers that appear. overwintering. Some people recom- Damage due to chemical application If you don’t have a lot of roses and mend a 2/3 prune. Other experts say is likely to be generalized whereas RRD really want to save a particular speci- the disease will just migrate downward is more likely to start in one location men, you can try pruning and monitor- so this technique is not a sure thing. and spread outward. ing, and hope for the best. Since some roses have been reported Mite Control to have some resistance to the mites What To Do? and/or the virus, it may be possible to Joan Allen, a diagnostician and There’s no cure for Rose Rosette breed resistant varieties in the future. assistant extension educator at UConn, Virus once a plant is systemic. You can, suggests that people might want to get however, try to control the spread of Early Detection their plants tested before they destroy the disease by controlling the mites Early detection and professional their prized roses. that vector it. opinions are critical. If you catch it early, Unfortunately, by the time symptoms Horticultural oil and insecticidal when only a cane or two is infected, become obvious, the disease may have soaps are routinely recommended you may be able to save the plant. spread to other plants. but require contact with the mites to be However, many experts recommend So, what do you do? effective and it’s difficult to reach mites removing symptomatic plants immedi- On one extreme, you can simply buried deep in the buds of growing tips, ately. Some even recommended remov- rogue out all of the roses that appear at the bottom of shoots, in leaf axils and ing adjacent plants just to be sure. to be infected, and adjacent roses if beneath leaf scars. e same would be Remember, since the disease can you’re really going for it. This is the true of non-systemic pesticides and remain dormant or latent for some safest approach but you’re going to feel miticides. time, plants may be asymptomatic pretty bad if you destroy a lot of roses As multiple generations of the mites (the disease is present but there are and discover, later, that it wasn’t really will develop until cold weather arrives, no symptoms). RRD after all. Neem Oil (azadirachtin) would require Symptoms On the other extreme, you can prune multiple applications over time. A number of sources recommend “The first symptoms the gardener out affected portions of plants and hope sulphur. While it is generally considered will see are hyper-prickles, strange that you’ve gotten it early, before it’s biorational, keep in mind that contin- colored new growth, foliage changes, become systemic. In this scenario, ued application of sulfur will acidify and distorted buds,” says Martin. you’re going to feel bad if the rest of soil. Also, sulfur should not be applied Look for: your roses get infected. within a month of using horticultural • Witches’-brooms “What I do is to cut off the affected oil. • Unusual coloration ... often reddish growth if it’s only on a cane or two, and Jennifer Olson, an assistant extension but sometimes mosaic wait to see how the new growth from specialist in the Plant Disease and • Deformed leaves and flowers that spot comes back,” said Martin. Insect Diagnostic Laboratory (PDIDL) • Small leaves with short petioles “If you can catch it at that phase and the at Oklahoma suggests three possible

May/June 2015 3 Connecticut Gardener options for the home gardener: • If possible, check the plants at the • Bonide All Seasons Horticultural & nursery for signs of infection. Dormant Spray Oil • Remove R. multiflora within • PureSpray GREEN – White Horti- 100 meters cultural Spray Oil (OMRI listed) • Space your plants out and avoid • Ultra-Pure Oil Horticultural Insec- overlapping canes and leaves. ticide/Miticide/Fungicide (hort oil) • Give your plants a good winter A number of chemical options exist prune and follow with a treatment of for growers and commercial applicators dormant oil but experts do not routinely recom- • Practice good hygiene   mend miticides for the home gardener • Monitor closely coping with Rose Rosette Disease. And, if you must spray, use “soft” Ballek’s There are a few reasons for this. OMRI-listed products such as light   Generally available miticides may horticultural oils, neem oil, insecticidal Garden Center not be effective on eriophyid mites and soaps and sulfur that are less likely to    may even kill predatory mites that prey cause collateral damage. on them or even lead to outbreaks of The Queen’s Garden Let Us Help You … spider mites.    I recently watched “The Queen’s Gar- Eriophyid mites tend to be host- den” on PBS and was fascinated to learn   specific so products that work on one that one of their major control methods - plant a butterfly  garden   species of plant may not work on for leaf-eating pests is garlic-infused another. - nurture native wildflowers water. Some organic gardeners add Several generations of mites may   onion or peppers to the mix. I was appear in a season so multiple applica- - savour the flavors of disappointed they didn’t do a segment   tions are necessary. heirloom edibles on the rose garden.    Finally, some of the products that - support native pollinators might work can only be used by a Testing    registered applicator. If the symptoms are obvious you - paint with annuals One approach is to try and control may not even need to test because    - plan for all-season color the mites in plants around an infected RRD has been diagnosed sympto-   matically for years. plant in order to prevent their spread. - invite hummingbirds to is would require pulling or spraying If you think your roses have RRD,  every two weeks from discovery until contact CAES’ Plant Disease Informa- your garden  September. tion Office. Go to www.ct.gov/caes and - revel in garden fragrance Also, keep in mind that mites can click on the appropriate link. develop resistance quickly. If you decide You can also send samples to - protect the honeybees to go the chemical route, you should UConn. Email [email protected]     - organically use a rotation of three or more products for more information. grow   that are proven to be effective on Wrap samples in newspaper or dry - understandyour  paper towels, seal in a plastic bag and eriophyid mites and are also “so” garden ecosystem on other life forms. store in your refrigerator until delivery.   Consult the Organic Materials More Information   Review Institute (OMRI) website at CAES is working on a fact sheet. www.omri.org for appropriate organic/ “Sharing Our Knowledge Until it’s available, Virginia Cooperative biorational products. Extension and Oklahoma State Uni- and Passion for Be Careful Out There versity have excellent fact sheets at Gardening   With  You!”  As always, study up before you start http://pubs.ext.vt.edu and http://   killing things. It can get complicated pods.dasnr.okstate.edu and might even backfire on you. Finally, if all this isn’t geeky enough 90 Maple Avenue In short, the use of miticides without for you, check out Ann Peck’s online East Haddam, CT 8878-873-860 ڞ addressing cultural issues isn’t a good book at www.rosegeek.com idea. Thanks to Richsrd Cowles and www.balleksgardencenter.com Our Recommendation Sharon Douglas at CAES, and The best approach, it seems to us ... Joan Allen at UConn, for their • Get your roses from trusted sources assistance in compiling this report. Ballek’s is an equal opportunity and inquire about susceptibility provider and employer.

Connecticut Gardener 4 May/June 2015