Tree Care and Maintenance Archive
Seasonal Tree Care Tips: Fall 2021
Healthy Trees are Defended Trees
By: Dr. Christine Buhl, ODF Forest Entomologist and Morgan Holen, Consulting Arborist
Most insects in our landscape are native, widespread and not pests. Some insects can become pests when their populations explode due to the availability of unhealthy trees (stressed by hot droughts, diseases, mechanical or storm damage, etc.) or a lack of natural controls (cold winters, natural enemies, etc.). It might be tempting to look for a silver bullet by blaming insects for tree damage or mortality, but in the urban environment, insect pests are typically not the primary cause of tree decline and their presence alone is generally not reason to remove a tree.
Since insect pests usually infest unhealthy or stressed trees, managing your trees for improved health and vigor can provide long-term protection for the tree. If your tree is already infested, the most effective treatment will be to determine and manage the primary cause of tree stress. The most common primary causes of tree stress are: hot droughts, planting of non-native species or any species not adapted to site conditions, poor site conditions, storm breakage or construction damage.
Pay close attention to the progression of symptoms to determine what the causal agent is. Often, damage from the above primary stressors slowly weakens a tree and symptoms may include slow foliage loss, flagging (when a tree's twigs or branches scattered throughout the crown turn brown, wilt, or die), or topkill, for example. Stressed trees, particularly droughted trees, are most susceptible to bark beetle attack, therefore the slow progression of drought symptoms can then be followed by the sudden appearance of multiple piles of brownish frass (sawdust) kicked out by bark beetles infesting the trunk. Mass attack by bark beetles (our most common tree-killing insect group) can kill a tree and turn the foliage red within a year.
Signs of bark beetles and woodborers are not uncommon, especially in western redcedars that are stressed due to poor site conditions, summer drought or mechanical damage. These trees were struggling before beetle infestation, but they may persist for many years with proper care and maintenance including supplemental watering during periods of drought.
In Lake Oswego, non-native ornamental pine trees are often attacked by sequoia pitch moth, which creates pitch masses near wounds from limbing performed in spring and summer. However, these insects are generally only an aesthetic issue and will not cause the tree to die. Keep in mind that excessive pitch is a normal and healthy wound response to pruning.
Visit the Oregon Department of Forestry’s Forest Health website to learn about insect and disease pests, including the examples pictured below.
Arborvitae (which is in the same genus as western redcedar) are often planted as “fences” in sun-exposed yards. This species prefers cool, moist habitat and will often struggle in yards especially during droughts and be finished off by woodboring beetles.
True fir species in the genus Abies (such as grand fir) prefer cool, moist habitat found at higher-elevations. Grand fir can persist in drier parts lower in the Willamette Valley, although they often reach a critical size that can no longer be supported by moisture on site and are finished off by fir engraver bark beetles (galleries under bark depicted on the right). Grand fir are also at risk from laminated root disease.
Birch prefer cool, moist habitat rather than yard and sidewalk locations and are often finished off by bronze birch borer beetle. Planting native water and paper birch varieties in clusters to provide each other shade, and adding mulch can prevent moisture stress and subsequent beetle infestation.
Douglas-fir is a moderately drought-tolerant tree but poor sites and persistent, intense droughts can cause needle then branch loss and finally the loss of the whole tree. Douglas-fir beetle often takes advantage of these trees when stressed by drought, storm blowdown and laminated root disease.
Even pine can become drought-stressed and lead to mass-attack by Ips beetles, especially if fresh pine slash is nearby to draw them in. Ornamental pines such as Scots and Mugo are often attacked by Ips. These pines are often attacked near pruning wounds by sequoia pitch moth, which cause large pitch masses all along the trunk (depicted on the right). Although this is unsightly, this insect is not a tree-killer.
Seasonal Tree Care Tips: Special Edition
After the Storm
Following the historic 2021 President’s Day weekend ice storm, people are in storm recovery mode and may be quick to think removal of storm damaged trees is the only option. The damage to trees across the region is dramatic, however not all trees that sustained damage are “goners” and many can be pruned and saved. The Oregon Department of Forestry has shared a variety of resources for the public to learn more about managing trees after the storm. These links and more are provided below.
Articles by the Oregon Department of Forestry, Urban and Community Forestry Program:
Tree City USA Bulletins by the Arbor Day Foundation:
Visit the Lake Oswego Tree Care and Maintenance Archives for additional information and resources in the Winter 2018 article on Tree Related Storm Damage.
Information on residential tree debris disposal is available here.
No permit is required to prune a tree; however, topping a tree is prohibited, and no more than 50% of the crown may be removed (cumulatively). In addition, no permit is required if an entire tree falls to the ground.
Emergency and Hazard Tree Removal
A permit is required to remove a hazardous or emergency tree. A tree qualifies under an Emergency permit if the condition of a tree presents an immediate danger of collapse, and is a clear and present hazard to persons or property. "Immediate danger of collapse" means that the tree is already leaning, and there is a significant likelihood that the tree will topple or otherwise fail and cause damage before a tree cutting permit could be obtained through the nonemergency process. "Immediate danger of collapse" does not include hazardous conditions that can be alleviated by pruning or treatment. You may proceed with removal of an emergency tree to the extent necessary to avoid the immediate hazard before obtaining a permit, but you must document the emergency situation in photographs. Within seven days of removal, the owner of the tree must apply for a retroactive emergency tree cutting permit and include photographs to demonstrate the emergency nature of the tree.
City crews continue to remove dangerous debris. Please be aware that many parks and open space areas remain closed due to hazardous conditions.
Seasonal Tree Care Tips: Winter 2021
What is an Arborist?
Images courtesy of: Andrew Koeser, International Society of Arboriculture, Bugwood.org
Arborist conducting visual tree inspection.
Trees are a long-lasting investment that may require substantial care and maintenance to maximize their benefits. Informed property owners can handle many of these responsibilities, but sometimes you’re better off calling a professional.
By definition, an arborist is an individual who is trained in the art and science of planting, caring for, and maintaining individual trees. Moreover, an arborist is a professional in the practice of managing trees with a superior understanding of the structure and function of individual trees. Chapter 55.02.020 of the Lake Oswego Code defines an arborist as a person who has met the criteria for certification from the International Society of Arboriculture (ISA) and maintains their accreditation.
Some arborists are tree service providers who specialize in providing services like pruning, removal, emergency tree care, and tree planting and maintenance. They may also provide insect and disease diagnosis, soils analysis, and plant health care treatments such as soil aeration and root invigoration. Tree service providers may also specialize in installing cabling and bracing for structural support. Other arborists provide consulting services, such as tree risk assessments, developing tree inventories and writing arborist reports, developing specifications for tree protection during construction, preparing landscape plant appraisals, or providing expert witness testimony for legal matters.
The ISA is a worldwide member organization promoting proper tree care and research. ISA certification is a voluntary process for professional arborists to demonstrate their knowledge and experience by passing a comprehensive exam and then maintaining their Certified Arborist credential through required continuing education. In addition to the Certified Arborist credential, the ISA offers certification specifically for utility specialists, municipal arborists, tree workers and climbers, aerial lift specialists and, Board Certified Master Arborist, the highest level of certification offered by ISA. Certified Arborists can also become Tree Risk Assessment Qualified (TRAQ) to demonstrate their knowledge of the fundamentals of assessing tree risk to help property owners make informed management decisions. TRAQ arborists are required by Lake Oswego’s tree code when arborist reports are required for hazard tree removal permit applications.
Consulting arborists are generally ISA certified, but many are also members of the American Society of Consulting Arborists (ASCA), a distinct organization focusing exclusively on consulting. ASCA members demonstrate an investment in their professional development by building relationships with other professionals who share their expertise. ASCA also offers a Registered Consulting Arborist (RCA) credential.
Arborists may also be members of the Tree Care Industry Association (TCIA), a worldwide trade association with a mission to advance tree care businesses.
Although these various types of arborist credentials cannot guarantee quality performance, they do attest to a certain level of knowledge. With so many different specialties in the world of arboriculture, make sure you are hiring the right arborist for your particular needs and don’t hesitate to ask for references, as well as proof of insurance.
Visit these sites to learn more:
Seasonal Tree Care Tips: Fall 2020
Images courtesy of: International Society of Arboriculture, Bugwood.org
Diagram of nutrient availability changing with soil pH.
Soils are an important part of a tree’s growing space and are often a limiting factor for growth in urban environments. Soils in urban landscapes can be altered during construction, leading to compaction and nutrient deficiencies. Compacted soils can restrict root growth or otherwise suffocate roots by reducing the flow of water and oxygen into the root system. Soil is the primary source of nutrients needed for tree growth and a tree’s ability to uptake nutrients can be affected by soil pH levels even if adequate nutrients are present.
A soil test should always be conducted before applying fertilizers to your tree. The results of a soil test will inform appropriate treatments specific to the tree species based on pH levels, nutrient deficiencies, soil texture, and porosity. An arborist can collect a soil sample and send it to a laboratory for analysis, then recommend treatments based on the results. Some treatments may include carefully aerating the soil to reduce compaction while avoiding root damage, and incorporating prescribed amendments or organic matter to modify soil pH, improve the tree’s ability to uptake minerals and nutrients, and invigorate root growth.
Visit these sites to learn more about soil management for tree health:
Mature Tree Care, a brochure by the International Society of Arboriculture, 2011.
Nutrition for Trees, a “Tree Care Tips” article by the Tree Care Industry Association.
How to Correct Soil Compaction, an article by Ed Macle, Regional Urban Forester, USFS Southern Region, USDA National Cooperative Extension.
K. Fite and E.T Smiley. Root Invigoration Program. Bartlett Tree Experts, Research Laboratory Technical Report.
Seasonal Tree Care Tips: Summer 2020
Retaining and Creating Snags for Wildlife
Images courtesy of: Cheryl Uchida. A snag in the front yard of a local residence right here in Lake Oswego.
Snags are standing dead trees and an important element of a healthy ecosystem. They provide roosting sites for birds and bats, denning sites for mammals, reptiles and amphibians, food storage areas for woodpeckers and squirrels, food for insect-eating birds and mammals, and critical nesting sites for nearly 40 species of birds west of the Cascade Mountain Range. Snags are a limiting factor for wildlife in urban and residential areas, but more and more, arborists are working with homeowners to retain or create snags where it can be done safely.
Dead and dying trees, and trees with peeling bark, cavities, decay fungi and other parts typically termed “defects” can provide tremendous wildlife benefits. Individual wildlife species have preferences for different habitats, so a wide variety of hardwoods and softwoods, short and tall snags, and small and large cavities scattered across a landscape is most beneficial. Don’t think you have to have a giant dead tree in your yard to provide valuable wildlife benefits. Some species, like chickadees, prefer short snags or tall stumps.
While large over-mature trees tend to have more defects and structural complexity, all trees are potential wildlife snags. Innovative arborists concerned about the loss of wildlife habitat in urban forests have developed thoughtful approaches to creating snags from live trees by mimicking natural succession. Some techniques involve girdling branches or tree trunks, reducing trunk height and creating a jagged top, drilling holes, cutting out cavities, and forming roosting slits.
Dead trees are not necessarily dangerous, but the potential for failure will increase as the tree decays over time. A general rule of thumb for managing risk potential is to reduce the height of the snag to at least 1.5 times the distance to a potential target (i.e. people or property that could be injured or damaged if the tree or part of the tree were to fail). For example, if you are considering retaining a snag located 60-feet from your home, reduce the height of the snag to no greater than 40-feet. Have your snag inspected by a qualified arborist periodically to help manage risk potential.
The Tree Code allows the City to require snag creation as a condition of approval for certain tree removal permits, most often for trees located in Sensitive Lands. The City’s contract arborist looks for other opportunities to suggest snag retention or creation to applicant’s that have received a tree removal permit. Moreover, some local residents are preserving wildlife trees on their own and helping to raise awareness about the critical need for snags in the urban landscape. In doing so, they find joy and excitement in watching wildlife visit and utilize the snag all year long.
The next time you’re considering removing a tree because it is dead, dying or has defects that you’re concerned about, consider working with an International Society of Arboriculture Qualified Tree Risk Assessor to explore opportunities to retain or create low risk snags for wildlife on your property. Feel free to contact the City’s Planning Department at firstname.lastname@example.org to determine whether or not a tree removal permit is needed prior to creating a snag since all trees measuring at least 6-inches in diameter are regulated by the Tree Code.
Visit these sites to learn more about retaining and creating snags for wildlife:
Snags – The Wildlife Tree. The Importance of Snags in Your Neighborhood, a Living with Wildlife article published by the Washington State Department of Fish and Wildlife, 2011.
A Snag in the Plan, an article by Tom Costello in the November 2013 Portland Audubon Newsletter, pages 8-9.
Arborists and Wildlife:Retaining Trees for Wildlife Habitat, an article by Brian French published in the February 2018 edition of Arborist News.
Seasonal Tree Care Tips: Spring 2020
Mulch: Numerous Benefits and Easy Application
Images courtesy of: Elizabeth Moss, West Virginia State University, Bugwood.org. An example of improper mulching, also known as the dreaded mulch volcano. Learn why and how to mulch the right way below!
Mulching is one of the most simple but beneficial things you can do for your trees. After the last frost, spring is a great time of year to refresh mulch around your trees, or to create mulch circles if you haven’t already. Not only will a mulch ring help to retain soil moisture and moderate soil temperature in a tree’s critical root zone, it also helps to reduce soil compaction, improve soil structure, protect trunks and roots from lawn mower damage, and minimize weed growth. However, too much mulch can suffocate the root zone and mulch piled against the trunk can cause decay. Only reapply mulch when needed to maintain 2- to 4-inches of cover.
Three Simple Steps to Create A Grass-Free Mulched Ring:
Using hand tools, carefully remove grass in a ring around the tree trunk. The circle should be at least 3-feet in diameter, but bigger is better, up to 10-feet for larger trees.
Apply a 2- to 4-inch deep layer of organic mulch, such as bark or wood chips, within the circle.
Make sure the mulch does not contact the tree trunk or bury the root flare.
Visit the sites below to learn more about mulching and look for the City’s free Tree Selection, Planting and Maintenance Workshop to be rescheduled in the Fall.
Mulching Trees and Shrubs, an article and YouTube video by The Morton Arboretum
Mulching Woody Ornamentals with Organic Materials, an OSU Extension Publication
How to Properly Mulch Around a Tree, a YouTube video by This Old House
Seasonal Tree Care Tips: Winter 2020
Tree Planting: To Stake or Not to Stake?
Images courtesy of: Fred Baker, Utah State University, Bugwood.org
An example of improper staking.
Staking is often the last step of the tree planting process, but is it really beneficial? Typically, rigid stakes are driven into the ground near the trunk on two sides and plastic or vinyl ties are wrapped around the tree trunk and attached to the stakes. We do this to provide structural support for the newly planted tree, but most trees do not need to be staked. Trees that are staked focus more energy into height and crown growth resulting in slender trunks that are less wind firm, while trees that are not staked focus more energy on root and trunk diameter growth, developing a strong support system. The ability to flex and bend in the wind creates a stronger tree.
When properly done, staking can be helpful for bare root trees or trees planted in very windy areas, but containerized and balled and burlapped nursery stock generally don’t need it. Improper staking is too common, with ties wrapped too tightly around the trunk or left on the tree long after establishment, which can lead to girdling over time.
Proper staking involves placing stakes low to help stabilize the root ball rather than the trunk, using flexible materials to tie the tree to the stakes allowing the trunk to move, and removing ties and stakes within the first growing season.
Next time you plant a tree, consider forgoing the stakes. The last step of your planting process could be adding a mulch ring around the tree instead! Mulch helps to insulate the soil and retain moisture, but too much mulch can be harmful. Generally, a 3” deep ring of mulch in a 4’ circle around your tree is sufficient, but don’t pile mulch against the tree trunk.
Visit the sites below to learn more about staking and call 503-635-0290 or email email@example.com to register for the free Tree Selection, Planting and Maintenance Workshop scheduled for 10:30 a.m. to 12 p.m. on April 11, 2019 at the City’s Maintenance Center (17601 Pilkington Road). More information about this workshop will be announced in the Urban & Community Forestry insert included inside your April HelloLO Newsletter!
The Myth of Staking, an article by Dr. Linda Chalker-Scott, Washington State University
International Society of Arboriculture, Best Practices for Staking a Tree Podcast
Selecting, Planting, and Caring for a New Tree, Oregon State University, EC1438, March 2016
Seasonal Tree Care Tips: Fall 2019
Insects and Diseases
Images courtesy of: Christine Buhl, Oregon Department of Forestry, Bugwood.org
Signs of sequoia pitch moth (Synanthedon sequoiae) on ponderosa pine.
Insect infestations and pathogen infections can threaten the health of your trees. Knowing what tree species you have can help you understand what types of insects and diseases it is susceptible to, and with proper care and maintenance you can manage to prevent problems before they start. Becoming familiar with what is normal for your trees can help you recognize abnormalities early on so that you can take action before it’s too late.
If you recognize abnormalities, the next step is to identify the symptoms (e.g., discolored foliage or top dieback) and look for signs (e.g., insect bore holes or mushrooms). Abiotic problems (caused by non-living organisms, e.g. drought stress or sunscald) generally follow a pattern or uniform display, whereas biotic problems (caused by living organisms, e.g. pests and pathogens) show symptoms in a more scattered or random display throughout the tree or groups of trees. Consider contacting a certified arborist who specializes in plant health care to help diagnose the problem. Once the problem is positively identified, a treatment protocol may be selected. As in the medical field, “treatment without diagnosis is malpractice.”
Not all insect and disease problems have a cure or are necessarily life-threatening. In fact, a variety of common issues are more aesthetic than detrimental, such as alder flea beetle which can skeletonize leaves, or sequoia pitch moth which is commonly misdiagnosed as bark beetle. Still, your tree may last for many more decades with pruning, systemic injections or cultural practices to manage plant health by optimizing site conditions (e.g., reducing soil compaction and improving soil health, mulching and supplemental watering).
Visit these sites to learn more about managing your trees to prevent and treat insects and diseases:
Insect and Disease Problems, an International Society of Arboriculture Brochure
Plant Health Care, an International Society of Arboriculture Brochure
Pacific Northwest Insect Management Handbook, a Pacific Northwest Extension Publication
Pacific Northwest Plant Disease Management Handbook, a Pacific Northwest Extension Publication
Common Tree Diseases and Pests, City of Portland Webpage
Alder flea beetle, Oregon State University Extension Fact Sheet
Sequoia pitch moth, University of California Integrated Pest Management Pest Notes
Seasonal Tree Care Tips: Summer 2019
Drought Stress Revisited
Images courtesy of: John Ruter, University of Georgia, Bugwood.org (dogwood tree).
Extended periods of drought and subsequent years of seasonal drought can cause stress in both young newly planted trees and mature well-established trees. Dry soil can cause tree roots to die and reduce a tree’s ability to absorb water when it finally rains. Drought stressed trees are also more susceptible to insects and diseases.
Some symptoms of drought stress include nonuniform wilting and yellowing of leaves, premature leaf drop, dieback and total death. Yard trees will benefit from slow, deep and infrequent watering during the dry season. Visit these sites to learn more about identifying drought stress symptoms and tips for preventing drought stress while avoiding overwatering:
Watering Mature Trees, a YouTube Video by the US Forest Service
Drought Stress in Conifers, an Oregon Department of Forestry Forest Health Fact Sheet
Drought Stress, article by The Morton Arboretum
How to Help Your Trees Recover from Drought, article by Davey
Spring 2019: Trees and Construction
Image courtesy of Morgan Holen, Consulting Arborist
Soil compaction, root severing or smothering, physical injury to trunks and crowns, drainage changes, and exposure from adjacent tree removal are all common ways that trees can be damaged during construction. These impacts can affect tree structure, survivability, and stability. Once a tree has been affected by construction damage, options for remedial treatments may be limited or ineffective. Therefore, successful tree protection requires special consideration prior to and throughout development activity.
Lake Oswego Code (LOC) Chapter 55 (link is external)requires a Tree Protection Plan for any development activities including, but not limited to, clearing, grading, excavation, trenching or tunneling, or demolition work on a property or site, that requires a development permit pursuant to LOC Chapter 50 (link is external), and to any activity related to stormwater structures, water and sewer lines/laterals, or irrigation that requires a plumbing permit, pursuant to LOC Chapter 46 (link is external). The Planning Department has added new conditions to Tree Protection Plans in a format that makes it clearer for the Builder to know when a certified arborist is required on a construction site to monitor and document tree protection measures. Detrimental tree root damage within a tree protection zone is a violation of the Tree Code and fees of at least $595 per violation are assessed. Click here to find a Lake Oswego Tree Protection Application Form or stop by the Planning & Building Services Department on the 3rd floor of City Hall (380 A Avenue) to speak with staff: Monday -Tuesday 7:30 a.m. - 3:00 p.m.; Wednesday 8:00 a.m. - 2:30 p.m. or Thursday-Friday 8:00 a.m. - 3:00 p.m.
Resources to learn more about avoiding tree damage during construction include:
Avoiding Tree Damage During Construction (link is external), a brochure by the International Society of Arboriculture
Treatment of Tree Damaged by Construction (link is external), a brochure by the International Society of Arboriculture
Best Practices: Setting Up a Tree Protection Zone (link is external), an ArborPodTM YouTube Video, 3.5 minutes
Reducing Tree (and Soil!) Damage During Construction (link is external), a Utah State University Webinar featuring Dr. Nina Bassuk of Cornell University, 1.25 hours
Winter 2019: Topped Trees
Topping: An Inappropriate and Prohibited Pruning Practice…Here’s Why!
Tree topping is considered an unacceptable pruning practice by the American National Standards Institute and many municipalities, including the City of Lake Oswego, prohibit topping. Lake Oswego Code Chapter 55 defines topping as the severe cutting back of a tree’s limbs to stubs 3-inches or larger in diameter so as to remove the natural canopy and disfigure the tree. Topping a tree in Lake Oswego constitutes removal which requires a permit if the tree is at least 6-inches in diameter. This harmful practice not only reduces the landscape value of your tree but it also results in stress that can lead to death, leaves stub wounds that invite decay fungi and insects, may result in rapid new growth with weak branch attachments and ultimately increases hazard risk potential. Topping by utility companies is allowed with a permit in furtherance of public safety where other pruning practices are impractical, so having the foresight to plant only small statured trees beneath utility lines is important. Check out these resources to learn more:
Why Topping Hurts Trees, a brochure by the International Society of Arboriculture
What’s Wrong with Topping Trees, a publication by Rita McKenzie, Urban Forester, Department of Forestry & Natural Resources, Purdue University
The Myth of Tree Topping, an article by Linda Chalker-Scott, Associate Professor Center for Urban Horticulture, University of Washington
Tree Care Tips: Tree Topping, a YouTube video by Stihl USA
Fall 2018 Autumn Leaves
Autumn…that time of year when days become shorter and trees becoming splendidly colorful. Then, the leaves drop, millions of them, and most of us head out to rake and rake and rake some more. This quarter’s article explains why broadleaved trees change color and discusses whether or not all that raking is worthwhile.
Leaf color comes from natural substances produced by leaf cells. Chlorophyll, which absorbs sunlight to produce energy is the most important and its what gives leaves their green color during the growing season. Flavonoids and carotenoids - yellow, orange and brown pigments - are also present throughout the growing season but are masked by the green chlorophyll. As the days become shorter, the leaves receive less sunlight and the chlorophyll begins to breakdown, thus revealing the yellow, orange and brown pigments that were there all along. What about that brilliant red color? It comes from anthocyanin which is produced through chemical reactions as overnight temperatures begin to cool, but not all trees can make anthocyanins. Check out these resources to learn more about leaf color and leaf drop:
Why Do Autumn Leaves Change Color (link is external), an excellent 2:20 minute Instant Egghead Video by Mark Fischetti for Scientific American
Autumn Color (link is external), a Research Laboratory Technical Report by Bartlett Tree Experts
There are pros and cons to raking and blowing all those leaves as they drop for weeks on end. Many people prefer a tidy yard, but consider the benefits of leaving a layer of mulched leaves to actually improve the health of your grass next summer. Leaves provide nutrients and can be beneficial in moderation, but keep in mind that leaves don’t belong everywhere and it is especially important to keep storm drains clear and prevent slippery walkways. Also, never leave diseased plant material on the ground which can spread foliar fungal and bacterial leaf spots and more. Learn more about the benefits of leaving some leaves and tips for creating leaf mulch by visiting:
“Leave” Them Alone: Lawn Leaf Management (link is external), Virginia Cooperative Extension Publication 430-521 by Mike Goatley Jr.
For the Greenest Yard, Leave the Leaves Behind: A new reason to reconsider raking or blowing leaves this fall (link is external), Consumer Reports article by Paul Hope
Want to Improve Your Lawn? Don’t Bag Those Leaves (link is external), from NPR’s All Things Considered
Emerald Ash Borer
Image courtesy of Leah Bauer, USDA Forest Service Northern Research Station, Bugwood.org
The emerald ash borer (EAB) is an invasive insect from Asia believed to have come to the United States in the 1990s through international shipping. The EAB’s primary food is ash trees and when an EAB eats, ash trees die. All 16 North American ash species, including our native Oregon ash (Fraxinus latifolia) are vulnerable; the Union for Conservation of Nature has declared five U.S. ash species as “critically endangered.”
EAB first started killing ash trees in Michigan, but now EABs have been detected in 35 states, despite efforts by regulators to contain them. Since 2002, this exotic insect has killed over 100 million trees throughout the country, causing more than $3.5 billion dollars in damages. While EAB has not been detected in Oregon yet, it is moving rapidly across the U.S., as far west as Boulder, Colorado. The transportation of infested firewood during the summer camping season is thought to be a main factor in the spread of EAB.
EAB can cause significant damage to Oregon’s urban and rural ecosystems, including along streamsides where many wild ash trees grow. “Wild ash forests and urban ash trees face a threat that has cost other states billions of dollars. Similar to wildfires, floods and other catastrophic threats, it is best to detect EAB quickly and deal with it swiftly,” said Wyatt Williams, the Oregon Department of Forestry’s invasive species specialist. Since 2006, the Oregon Departments of Forestry and Agriculture, and the U.S. Department of Agriculture have surveyed Oregon for EAB and found none…yet.
Oregon is one of the few western states that has a statewide EAB plan to protect and limit harm to the state and prepare its communities and citizens. The Oregon Invasive Species Council facilitated the plan’s development. Funding for this project was provided by the U.S. Forest Service Region 6 Western Competitive Grant for the “Forest Pest Detector Program.” The Oregon Readiness and Response Plan includes a statewide risk assessment, methods of early detection, and quarantine and communication plans.
Next time you head out for a family camping adventure, please remember to buy your firewood where you burn it! Check out these resources to learn more:
To report a suspected invasive species, visit oregoninvasiveshotline.org or call 1-866-INVADER.
Pruning Young Trees
Now that you’ve planted the right tree species in the right place, young tree structural pruning is one of the most important things you can do. Thoughtful and proper pruning early in the life of a tree can reduce the need for maintenance over time, improve structure and strength, and perhaps increase the tree’s lifespan. When the tree is first installed, limit pruning to the removal of dead and broken branches only. The tree needs two to three years to recover from transplanting shock, and as much foliage as possible during this time to create and store energy through photosynthesis while its roots become established and begin to expand. In years three or four, you can begin to remove defective branches and thin excessive branches. Around years five to seven, you’ll want to select the lowest permanent branches and check for even branch spacing throughout the crown. After that, inspect the tree early each spring and prune dead and defective branches as needed. Remember, every pruning cut should be made for a purpose and with good intention. It is critical that you use the right tools and make proper cuts to promote wound closure and avoid damage. When in doubt, consult with an ISA Certified Arborist, and be on the lookout for free annual pruning workshops hosted by the City’s Urban & Community Forestry program. Check out these resources to learn more:
Tree Related Storm Damage
Did you know that nearly 15 times more trees failed during the Columbus Day storm in October 1962 than during the eruption of Mount St. Helens in 1980? While the Columbus Day storm was exceptional, with wind gusts reaching 116 mph in downtown Portland, tree-related storm damage is not uncommon in our region. This time of year, saturated soils, strong winds, and freezing rain may lead to failure of part or all of a tree, even a seemingly healthy one, which may result in lasting impacts to your landscape. However, it is important for property owners not to make hasty decisions during clean-up that can threaten their own personal safety or exacerbate property damage. There are simple steps to follow in response to tree-related storm damage to stay safe and get your landscape back in order. Check out these resources to learn more:
Fall is a great time for planting new trees in Oregon. Selecting the right tree species and the right planting location is a decision that can have an impact on your landscape, and perhaps your neighborhood, for decades to come. There are many factors to consider in selecting the most suitable and desirable tree species for your site, and following simple steps for installing a new tree will help to avoid common problems caused by improper planting. Check out these resources to learn more about selecting and planting new trees:
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Trees and turfgrasses are commonly planted together in residential landscapes, but are not so easily compatible. They compete for water, sunlight, nutrients, and root space. Tree trunks are easily damaged by lawnmowers. And, what about those expansive surface roots damaging your lawnmower blades?
Understanding how to better manage the competition will help you take advantage of the variety of benefits trees and turfgrasses can provide. For example: surface rooting throughout lawn areas can be prevented with proper tree species selection, soil improvements, and providing a slow, deep, and infrequent watering beneath tree canopies; a grass-free ring of bark mulch is a good alternative around tree trunks to help keep lawnmowers away, in addition to a variety of other benefits the mulch will provide; and, new varieties of shade tolerant grasses are becoming more available.
Learn more about trees and turfgrasses by visiting these sites:
Trees and Turf Brochure (TreesAreGood.org Tree Owner Information)
Tree roots coming to the lawn surface can be a real headache (Seattle Times, Ciscoe Morris, October 29, 2015)
Mechanical Damage to Trees: Mowing and Maintenance Equipment (Purdue Extension, FNR-492-W)
Tree Watering (Arbor Day Foundation)
Plant Guide: Water-Efficient Plants for the Willamette Valley
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English ivy is the most common invasive plant in Lake Oswego. It is an aggressive species with no natural enemies that grows and reproduces quickly, outcompetes native plants like wildflowers and ferns, and has vines that commonly grow up tree trunks with detrimental effects. English ivy competes with trees for water and nutrients, deprives tree bark of normal contact with air and microorganisms, and increases susceptibility to wind stress and the risk of canopy or whole tree failure.
Property owners can remove ivy from trees by cutting the vines at chest height in a ring around the trunk with pruners, loppers or saws. Pull the lower portion of the cut vine off of the tree trunk carefully to avoid bark injury, and pull or dig out the attached roots. Clear a 3- to 5-foot ring around the base of the tree to help prevent or postpone re-growth up the trunk. The upper portion of the vines can be left on the tree because it will die back.
Learn more about the detrimental effects of English ivy and how to remove it by visiting these sites:
Factsheet: Ivy Removal in a Home Landscape
Video: How to Remove Ivy
Explore: The Ivy Files
Seasonal Tree Care Tips: Preparing Trees for Fall and Winter
Fall is a great time to be prepare your trees for the winter weather ahead. With leaves falling from trees, branch structure and defects are easier to see, so it’s a great time of year to have your trees inspected by an ISA Certified Arborist. Branches may need to be pruned, cabled or braced to help prevent storm damage. Fall is also a great time of year to mulch and fertilize. Mulch helps to insulate the soil and retain moisture, but too much mulch can be harmful. Generally, a 3” deep ring of mulch in a 4’ circle around your tree is sufficient, but don’t pile mulch against the tree trunk. Fertilizer should never be applied without first obtaining a soil test to check for nutrient deficiencies.
Visit these sites to learn more about preparing your trees for winter:
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Trees provide desirable benefits in the landscape, but may become hazardous when they have defects resulting in increased failure potential and are located within striking distance of targets—such as people, vehicles, buildings, or other infrastructure—that could be injured or damaged by tree failure. Reasonably assessing the potential risk of injury or damage that a tree may cause and managing to reduce risk is called Tree Risk Assessment. The Tree Risk Assessment Process involves a systematic evaluation of an individual tree along with review of site use, and is a specialized area of expertise that should be undertaken by a trained professional. An ISA Tree Risk Assessor Qualified Arborist can assign a hazard risk rating to your tree and provide management recommendations to reduce risk, such as relocating potential targets, pruning to remove defective parts, or whole tree removal. It is a property owner’s responsibility to ensure that their trees are reasonably safe and to manage their trees in order to reduce risk. Visit these sites for tips on recognizing tree risk and know when to contact a professional:
- Trees Are Good: Managing Hazards and Risks
- McLean, D.C., et al, 2014. “Is My Tree Safe? Recognizing Conditions that Increase the Likelihood of Tree Failure.” ENH1246. Environmental Horticulture Department, UF/IFAS Extension.