Rose Rosette Disease (RRD)

Mark Webber • April 22, 2018

Don't ignore this issue in your landscape.

Photograph Source Mk Webber2018

Rose rosette disease (RRD), a disease believed to be caused by the recently identified Rose rosette virus,
has been spreading through much of the wild rose population of the Midwestern, Southern, and Eastern
United States for years. It has been confirmed in cultivated roses in Ohio and other states. RRD is of great concern to many landscape managers and property owners because it is known to be lethal to the wild multiflora rose (Rosa multiflora)

More so, it is potentially lethal to many ornamental rose species and cultivars. It has long been known that the eriophyid mite, Phyllocoptes fructiphilus, spreads the disease.

Symptoms
Symptoms of RRD are highly variable, depending on the species or cultivar of rose affected. This variability
can complicate diagnosis. Some of the more recognizable symptoms include rapid elongation of new shoots followed by a development of witches’ brooms or observed by the clustering of small branches. Leaves in the witches’ broom are small, distorted, and may have a conspicuous red pigmentation, although red pigmentation is not a consistent symptom. Canes on some species or cultivars develop excessive growth of unusually soft and pliable red or green thorns that may stiffen later. When this symptom is present, it is diagnostic for RRD. Symptomatic canes may also be noticeably thicker than the parent cane from which they emerged, or they may grow in a spiral pattern. Flowers may be distorted
with fewer petals than normal, and flower color may be abnormal. For example, flowers that are typically
a solid color may be mottled. Buds may abort, be deformed, or be converted to leaf-like tissue. Infected rose plants often die within one to two years.

When all of the above symptoms are present, diagnosis is relatively straightforward. However, a diseased plant
may exhibit few of these symptoms, especially in the early stages of the disease. By the time symptoms are severe and recognizable, the disease is likely to have already spread to neighboring plants.

Some symptoms, such as leaf coloration, may be subtle. Although some diseased plants develop very obvious red pigmentation, others exhibit a less striking reddish-pink color on leaf undersides or along the margins of otherwise green leaves. Because the new leaves of many rose cultivars normally have reddish pigments, it may be difficult to determine whether the reddish color is abnormal or not. Therefore, it is important to continue to monitor symptoms on suspect roses.

On RRD-infected plants, the reddish color does not go away, whereas on healthy plants, the reddish color usually
disappears as the leaf matures. Witches’ brooms on some diseased plants may be an unusual color of green that can be mistaken for symptoms of a nutrient deficiency. However, nutrient deficiency should affect the whole plant. If these symptoms appear only on parts of the plant, they are probably not due to nutrient deficiency, and RRD is more likely.
The witches’ broom symptom itself is not necessarily diagnostic for rose rosette disease. This symptom can also occur in response to certain types of herbicide injury. For example, if glyphosate, the active ingredient of the herbicide Roundup, contacts green tissue of rose plants in the fall, it is moved by translocation to the buds, and symptoms do not become evident until those buds emerge the following spring. Witches’ brooms with yellow, narrow leaves on clusters of shoots are typical of glyphosate injury. The commonly used broadleaf herbicide 2,4-D can also cause leaf distortion on roses. Unless plants are injured again, symptoms of herbicide injury should disappear by the following year.

Other symptoms of rose rosette disease that may be
expressed include:
• Blackening and death of the canes on some cultivars.
• Short internodal distances.
• Blind shoots (shoots that do not produce a flower)
That remains blind.
• Greater sensitivity of the reddish purple tissue to frost.
• Roughened, “pebbly” texture to leaves.
• Increased susceptibility to the fungal disease, powdery
mildew. This is especially evident when nearby
roses known to be highly susceptible to powdery
mildew do not develop signs of this disease.

Control
No effective control is available for rose rosette disease in existing infected rose plants, but the disease may be
prevented from spreading to healthy plants by using a combination of the following approaches.

Cultural Control
Early detection of the disease is the key to effective cultural control. Any suspect roses should be removed
and destroyed immediately or monitored for continued symptoms and removed as soon as presence of RRD
is ascertained. In some areas, burning is permitted and can be used to destroy diseased plants. If burning is not allowed in the area, plants should be bagged and removed. Diseased plants that have been uprooted should not be allowed to remain in the vicinity of healthy roses because they can continue to serve as a source of inoculum.

If possible, R. multiflora plants — which frequently serve as the source of inoculum — should be eliminated from the immediate vicinity (325 feet radius) of rose nurseries and gardens. Locations where individual multiflora rose plants have been removed should be monitored for regrowth, and any regrowth should be removed and destroyed. Multiflora rose over larger areas is difficult to control and complete removal may not be practical. To prevent infection of new transplants, avoid planting cultivated roses on hilltops or downwind of known multiflora rose plantings where the cultivated rose transplants are more susceptible to invasion by the mites.
Space plants so that canes and leaves do not touch each other. Eriophyid mites do not have wings and must crawl from plant to plant. Proper spacing makes it more difficult for the mites to move within a planting.

Resources
Amrine, J. W., Jr., and D. F. Hindal. 1988. Rose Rosette: A Fatal Disease of Multiflora Rose. West Virginia
University Circular 147. Morgantown: West Virginia University.

Amrine, J. W., and S. Zhao. 1998. “Research on Aerial Dispersal of Phyllocoptes fructiphilus (Acari: Eriophyidae),
Vector of Rose Rosette Disease.” American Rose, March 1998, 28-29.

Laney, A. G., K. E. Keller, R. R. Martin, and I. E. Tzanetakis. 2011. “A Discovery 70 Years in the Making:
Characterization of the Rose Rosette Virus.” Journal of General Virology 92:1727-32.

Peck, A. 2007. Rose Rosette: A Web Book. Updated May 2007. www.rosegeeks.com

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Photo Source (Tree Dictionary) This week I spent some time helping the team at Mark Webber's Landscaping conduct a tree risk assessment of a very large Ash tree. After the Ash inspection, I then inspected a number of other trees on the subject landscape. The property owner had unfortunately had her trees been mistreated by improper pruning. The term “seal,” rather than “heal,” is used to describe tree wound closure, since the wound still exists inside the tree even after it no longer shows on the outside. A properly pruned tree will create a better tree; however, a poorly pruned tree will result in a deteriorated condition. Trees have a natural defense response to wounds and pruning cuts. They form four types of walls to compartmentalize the area thus preventing the spread of decay organisms. However, if you prune too much from a tree, it will not have the energy resources to have the energy to compartmentalize. Proper pruning techniques and timing are critical to long-term tree health. The most important principle to remember is that each cut has the potential to change the tree considerably. Tree pruning needs to be well thought out and based upon what science and the Best Practices of the International Society of Arboriculture. In this case, the client's trees were excessively pruned by removing all of the subject inner branches resulting in a tree branch that looks like a lions tail. Lion's tail pruning creates tree branches that are likely to fail under normal weather conditions. In the case, the recommendation to this client was to do nothing or not to prune the subject trees for at least the next 6-9 years. Pruning Dose As a tree gets older the more difficult, it becomes for the plant to manage excess cuts. (See Chart/photograph above) When trees are young [Y] great amounts of symplast maintaining wood [L] can be removed. Symplastless wood is a term that is lucid to describe a tree or piece of wood or tree part that no longer maintains a symplast. As the tree matures [M] less symplast maintaining wood should be removed, and symplastless wood removal should increase [D]. As the tree approaches over maturity [OM] very little symplast maintaining wood [L] wood should be removed, and great amounts of symplastless wood [D] should be removed. Bottom Line If too many tree branches are removed or if the cuts are too large in older trees will result in further deterioration to the subject tree that may result in the loss of your valuable tree. You should use only Certified Arborist to make decisions about how to best manage your trees. Here are some important tips to follow for better trees: • Start training trees with pruning while they are young and newly established. • Minimize the number of live branches removed at any one time. • Use proper cuts. Watch the branch collar and/or branch bark ridge. • Pruning dose should be determined by overall tree health. • Reduce live-tissue pruning during times of drought. • Remove smaller branches rather than larger branches. • Do not top trees for any reason (heading cuts). • Prune when trees are biologically active to expedite wound sealing. • Do not use tree wound dressings. References http://www.treedictionary.com/DICT2003/tree_pruning/dose/chart.html Tree Pruning Essentials. Lindsey Purcell. Purdue University.2015 McKenzie, R. 2008. What’s Wrong with Topping Trees?, FNR-FAQ-14-W. Purdue University Cooperative Extension, West Lafayette, Ind., USA.
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