OREGON STATE UNIVERSITY EXTENSION SERVICE

Homeowner Guide to Managing Bronze Borer in the Upper Klamath Basin CC BY-NC, CC 2.0 Ian Kennedy Photo: Nicole Sanchez and Daniel Leavell

Introduction Identification (BBB) is a in the family. It is olive to brown in color with a coppery metallic reflection (Figure 1). Adults are about a half-inch long (females tend to be slightly larger). Males and females have slightly different head color. Larvae, the immature and most destructive form of the pest, are creamy white, about an inch long when fully developed, and have a distinct flat head (Figure 2, page 2). Both larvae and adults are difficult to find. Signs of the ’ damage are easier to detect than the actual insects, which spend most of their lives inside the . Wilted near the top of the tree are often the first identifiable sign of the borer’s presence, followed by twig and branch dieback. Photo: J.A. Davidson, Univ. Md, College Pk, Bugwood.org Life stages and damage Figure 1. Adult bronze birch borer Larvae hatch from eggs laid on the surface of the birch tree and bore into branches or the tree trunk. Larvae feed in the cambium layer of the tree. The cambium is between the and of the tree Nicole Sanchez, MS, assistant professor (practice), horticulture; (Figure 3, page 2), and is where the tree’s nutrient and Daniel Leavell, PhD, assistant professor (practice) and Extension water transport systems are located. Extensive feeding agent, forestry, natural resources, and fire science; both of Klamath by bronze birch borer larvae disrupts the flow of water Basin Research & Extension Center, Oregon State University

EM 9189 March 2018 1 Photo: David G. Nielsen, The Ohio State University, Bugwood.org Photo: David G. Nielsen, The Ohio State University, Bugwood.org Figure 2. Bronze birch borer larva Figure 3. Bronze birch borer pupa in tree cambium

and nutrients in the tree and kills , branches, and Cultural practices eventually the entire tree. Because it is under the bark, Different birch species have varying levels of this damage is impossible to see without removing susceptibility to bronze birch borer. For future birch the bark (Figure 4). After growing to about one inch plantings in areas where BBB is present, select a in length, larvae pupate inside the tree (Figure 3). resistant type. See the U.S. Forest Service’s “Forest “Rumpled” or wrinkled looking bark is another sign of & Disease Leaflet 111” (http://oregonstate.edu/ BBB presence; it is found on small trunks or at the base dept/kbrec/sites/default/files/bronzebirchborer_0. of branches where they join the trunk (Figure 5, pdf) for more detailed information on birch species’ page 3). Cambial feeding at branch bases cuts off water susceptibility to BBB. Native birch species are the most and nutrients to the branch, causing the individual resistant to this insect. branch to die back. Larval development takes 1 to 2 years, depending on the climate and length of the The transport of is one of the main growing season. ways BBB is moved to new locations. Purchasing locally sourced firewood can reduce the possibility of Adults emerge out of the pupal casings and feed on introducing BBB into a non-infested area. the leaves of the tree but rarely cause extensive damage. The D-shaped exit hole made by the adult emerging BBB cannot kill healthy and is most likely to from the tree is another sign of the insect’s presence attack old, stressed, or drought-stricken trees. While (Figure 6, page 3); it is sometimes accompanied by many homeowners may not place a high priority on brown staining on the bark. The D-shaped emergence watering mature trees, this can be a key strategy for holes are usually found above chest height on the tree preventing BBB damage in dry areas. Birch trees tend to and often are undetected until well after damage in the be shallow-rooted and respond well to watering. canopy is apparent. Removing trees too damaged to recover disrupts the BBB life cycle and can slow the spread of the What homeowners can do pest. Removal is also the only option for trees with Assessing damage levels An illustrated scale can help homeowners assess tree damage and the likelihood that treatment will prove beneficial. The scale ranges from 1 (healthy tree) to 5 (dead/dying tree) (Figure 7, page 4). Trees can be preserved if the damage is caught and treated early. Generally, trees with level-1 to level-3 damage have a good chance of recovery. With level-4 damage, the tree is less likely to recover, but recovery is still possible. However, a tree with level-5 damage is dead and needs to be removed. Landscape practitioners report that recovery is possible if treatment is applied while trees

are actively growing and less than 50 percent of the tree Photo: Daniel Leavell, © Oregon State University canopy is affected. Figure 4. Bronze birch borer damage caused below the tree bark 2 Upper Klamath Basin case study: BBB in Klamath Falls Bronze birch beetle was first detected in Oregon in 2003, appearing in Portland and migrating south in the years since. Recently, it was detected in Bugwood.org Klamath Falls (2017), where the timing of BBB adult spring emergence is not yet known. However, in areas with a climate similar to Klamath Falls, adults emerge in May and June. Because the exact timing of the BBB’s life cycle is not known in Klamath Falls, the use of non-systemic products, such as Carbaryl, may not be as effective because the chemical has to come in contact with the eggs and newly hatched larvae. Watering, however, is a key preventive strategy. In one Klamath Falls neighborhood severely impacted by BBB, observation suggested a correlation between

Photo: Steven Katovich, USDA Forest Service, irrigated yards and healthy trees, while trees in non- Figure 5. “Zig-zig” raised areas of bark are irrigated yards were the most severely affected. evidence of larval feeding Efforts to trap adult BBB in Klamath Falls after detection in 2017 were not successful. Additional level-5 damage. The success of your treatment plan trapping efforts are planned over the next several may be affected by the actions (or inactions) of your years, along with the use of predictive modeling, to neighbors regarding control of this pest. If you find that determine the likely emergence time frame for BBB BBB is a problem in your landscape, treatment is not adults in the Upper Klamath Basin. Understanding only beneficial to your trees but also to trees in your the timing of adult emergence will increase neighborhood. treatment options for homeowners with birch trees. Chemical practices Systemic insecticides can be effective for homeowners against BBB. Depending on the application followed by regular watering because it can take a large method and product, you may have to hire a licensed tree several months to fully draw in these products. In pesticide applicator. Tree injection products, for areas with no summer rains, watering is necessary for example, are only available to professional applicators. the tree to draw the pesticide from the soil. Read the pesticide label before purchasing a product to ensure it is intended for use on ornamental trees, Notes on pollinator conservation including birch. Similar products with the same active Birch trees are wind pollinated. However, because ingredients that are not formulated for trees will not be from birch may be attractive to bees, effective and could even damage your tree further. you should apply systemic insecticides only after Carbaryl is a non-systemic insecticide that can be flowering has occurred in the spring to reduce possible applied as a spray to the trunk and lower limbs of trees; pesticide exposure to bees. Also, do not apply systemic it should be applied during the active growing season. insecticides to the soil (spray, soil drench, or injection) Carbaryl and other non-systemic products are only useful when they come into contact with BBB eggs and newly hatched larvae and, therefore, must be timed to

adult emergence (typically a 2- to 3-week window that will vary each year due to weather and temperature fluctuation). Systemic insecticides such as or Oregon State dinotefuran, depending on the pesticide label, can be © applied as a tree injection, soil injection, or soil drench. They are effective in controlling larvae feeding inside the tree. Standard, commercial practice for BBB in European Birch (the birch species most affected in the Upper Klamath Basin) is trunk injection of emamectin Photo: Robin Rosetta, University benzoate every 3 years, or trunk injection or soil drench Figure 6. Exit hole made by adult bronze birch borer emerging of imidacloprid every year. Soil drenches should be from the tree 3 Mulch

6-foot radius for adult tree, avoid contact with trunk © Oregonian Publishing Co. Reprinted Oregonian© Co. Publishing with permission. Illustration: Photos: Daniel Leavell, © Oregon State University Figure 7. Scale of damage from bronze birch borer, ranging from a healthy tree (level-1 damage, on the left) to a tree that has to be removed (level-5 damage, on the right)

when that are attractive to bees are blooming OSU Extension publications underneath treated trees. Always follow pesticide label • Pacific Northwest Insect Management Handbook instructions. The label is the law. https://pnwhandbooks.org/insect/hort/ It is not known at this time how much pesticide is landscape/hosts-pests-landscape-/ expressed in birch pollen the year of application or birch-betula-bronze-birch-borer in the year following application of various systemic • How to Reduce Bee Poisoning from Pesticides pesticides. Depending on the application method and (PNW 591): https://catalog.extension. rate, imidacloprid and certain other pesticides may oregonstate.edu/pnw591 persist into the following year. Dinotefuran usually Additional resources does not persist in trees as long as imidacloprid and, therefore, may be less likely to be expressed in • U.S. Forest Service Forest Insect & Disease et pollen in the spring. Homeowners may consider using 111, Bronze Birch Borer http://oregonstate. dinotefuran, particularly when fall applications are edu/dept/kbrec/sites/default/files/ necessary. bronzebirchborer_0.pdf • OSU IPM Bronze Birch Borer Page http:// For more information oregonstate.edu/dept/nurspest/bronze_birch_ For more information or guidance on managing borer.htm BBB in your area, contact horticulture faculty at your • University of Insect Page https:// local Extension office. The following are some useful www.extension.umn.edu/garden/insects/find/ publications. bronze-birch-borer/

Use pesticides safely! Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use. Read the pesticide label—even if you’ve used the pesticide before. Follow closely the instructions on the label (and any other directions you have). Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use. © 2018 Extension work is a cooperative program of Oregon State University, the U.S. Department of Agriculture, and Oregon counties. Oregon State University Extension Service offers educational programs, activities, and materials without discrimination on the basis of race, color, national origin, religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital status, familial/parental status, income derived from a public assistance program, political beliefs, genetic information, veteran’s status, reprisal or retaliation for prior civil rights activity. (Not all prohibited bases apply to all programs.) Oregon State University Extension Service is an AA/EOE/Veterans/Disabled. Published March 2018 4