Tree Care and Maintenance Archive

Seasonal Tree Care Tips: Winter
Fruit Tree Maintenance

Caring for fruit trees might seem intimidating at first, but it’s easier than you may think. Routine maintenance and annual pruning can help promote fruit production, improve fruit quality, develop strong structure to support a heavy crop of fruit, and maintain the overall size of the tree for easy and safer harvesting.

At the start of winter, remove any dropped rotting fruit from the ground or fruit remaining on the tree to help limit fungal diseases. Then, apply a 3-inch layer of arborist chip mulch on the ground surface to help moderate soil temperature and retain soil moisture, just avoid piling mulch against the tree trunk. Then, get ready to prune!

Winter is generally the best time of year to prune deciduous fruit trees such as apples, pears, and cherries. Plan to prune between December through February, when all danger from fall or early winter freeze has passed and before full bloom in spring. There are many exceptions for certain other types of fruit trees. For example, apricot trees are highly susceptible to water-borne fungal diseases and should generally be pruned during the dry season, no later than August. Check with your local tree nursery or the Oregon State University Extension for advice on when to prune other fruit tree species.

Fruit tree diseases can be limited by sterilizing your pruning shears before use with denatured alcohol (e.g., isopropyl alcohol or acetone) and by learning to make proper pruning cuts. “Training and Pruning Your Home Orchard” is a great resource for learning how to actively manage your fruit trees.

Learn more about fruit tree maintenance by visiting these sites:

• Planting and caring for a fruit tree 
• Growing tree fruits and nuts in the home orchard 
• Pruning Guide
• Get a leg up on fruit tree problems with dormant oils 

Seasonal Tree Care Tips: Fall 2024
For a  Healthier Yard, Leave the Leaves

As the weather becomes cooler and the days become shorter, deciduous trees shed their leaves to conserve energy, and folks tend to head outside to rake and blow and bag the leaves for tidy yards. This fall, consider the many benefits of letting fallen leaves stay on your property, at least some of them. Not only will you save time and money, but you will also have a healthier yard, too!

Leaves create natural mulch as they decay, providing beneficial organic matter to the below-ground ecosystem. Nutrients are released into the soil as the leaves break down, reducing the need for fertilizer and providing food for micro-organisms that make the soil healthier for plants to grow stronger.

Leaving the leaves also provides valuable habitat for bird, mammal, reptile, amphibian, and insect species. Many invertebrates and pollinators rely on leaf litter for food and shelter, including moths, butterflies, and bumble bees that overwinter in the landscape. The Xerces Society for Invertebrate Conservation recommends leaving leaves whole to provide the best cover, rather than shredding them with your lawn mower which can destroy eggs, caterpillars and chrysalis hiding in the leaves.

Additionally, leaf mulch helps to:

• Suppress weed growth;
• Protect the soil surface by slowing stormwater runoff, reducing soil erosion;
• Retain soil moisture, reducing stress to plants during times of drought; and,
• Moderate soil temperate, keeping roots warmer during the winter and cooler in the summer.

A layer of leaves should be at least a couple of inches thick to mimic natural ecosystems. Rake leaves around trees, shrubs, and garden beds or to areas of bare or compacted soil. A thin layer of leaves can even benefit turf grass. Still too many leaves? Share them with a neighbor! Just be sure to keep storm drains clear and move leaves from hardscapes to 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 benefits of leaving leaves for a healthier yard by visiting these sites:

• Leave the Leaves, Oswego Lake Watershed Council 
• Leave the Leaves: Winter Habitat Protection, Xerces Society for Invertebrate Conservation
• Why You Should Leave the Leaves, National Wildlife Federation
• This Fall, Leave the Leaves! An article by Brooke Franklin, NRCS

 

Seasonal Tree Care Tips: Summer 2024
Tree Risk Assessment

Illustration Credit: International Society of Arboriculture, Bugwood.org

It is impossible to maintain trees free of all risk, but balancing tree risk with the many benefits that trees provide can be managed through Tree Risk Assessment (TRA). TRA is a specialized field of arboriculture. Competent Tree Risk Assessors have extensive training, skills and experience, as well as certifications and qualifications, and assess risk potential using standardized procedures and methodologies. The assessor must have a base-level knowledge of trees, as well as an understanding of species-related failure profiles, be able to identify site factors that may be of concerns, and have an eye for recognizing the sign and symptoms of structural weaknesses. Their reports should include findings and evidence to support the assigned risk rating.

Basic TRA is limited to conditions that are visible from the ground at the time of the assessment. In some cases, the assessor may recommend an Advanced Assessment to obtain more detailed information about a specific tree part or defect. Advanced Assessment may include climbing into the crown for an aerial inspection, assessing internal decay using drilling or sonic devices to more accurately locate and determine the extent of decay, excavating soil around the root collar for root evaluation, or other methods. Trustworthy Tree Risk Assessors will know when to bring in an expert to provide support for these unique types of assessment.

Using the International Society of Arboriculture (ISA) Best Management Practices (BMP) for Tree Risk Assessment, a Tree Risk Assessor Qualified (TRAQ) arborist can assign a risk rating to trees by evaluating and classifying the likelihood of a tree failure impacting a target and estimating the consequences of that tree failure. According to the ISA BMP, “A tree is considered hazardous when it has been assessed and found to be likely to fail and cause an unacceptable degree of injury, damage, or disruption—that is, it poses a high or extreme risk.” The criteria for issuance of a hazardous tree cutting permit in Lake Oswego Code Chapter 55 is based on this threshold.

The most challenging aspect of conducting a TRA is rating the likelihood of failure. Each defective part, whether it be a branch, a codominant stem, the entire tree, or other parts of the tree, may require examination and different treatment recommendations. Likelihood of failure is rated as improbable, possible, probable, or imminent. A tree or tree part that has a high likelihood of impacting a target with significant or severe consequences of failure cannot rate extreme or high risk if the likelihood of failure is not probable or imminent. Conversely, a tree or tree part with a probable or imminent likelihood of failure cannot rate extreme or high risk if the likelihood of impacting a target is unlikely or only somewhat likely, regardless of the consequences.

One of the simplest ways to reduce risk is to move the target, such as a bench, picnic table or play structure. When moving a target, like a house or bus stop, is not possible, treatments may include periodic monitoring, pruning, installing structural support such as cables or brace rods, whole tree removal, or other treatments. The TRAQ arborist will assign a residual risk rating based on the recommended treatment. While the arborist can assign risk ratings and prescribes treatment recommendations and explain the residual risk remaining after such treatments, property owners have a duty of care responsibility to manage risk potential to acceptable levels and to prioritize and implement recommended treatments to reduce risk depending on the risk rating and the property owner’s risk tolerance.

Contact a local arborist and ask about conducting a TRA to help manage the long-term health and care of your trees to reduce risk potential and maximize the environmental, social and economic benefits trees provide.

Verify that your arborist is ISA Certified and Tree Risk Assessment Qualified at www.treesaregood.org.

Learn more about Tree Risk Assessment by visiting these sites:

• Trees Are Good: Managing Hazards and Risks
• International Society of Arboriculture, Tree Risk Assessment Qualification
• 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. 

 

Seasonal Tree Care Tips: Spring 2024
Invasive Ivy Removal 

Ivy up tree trunks - Spring 2024.jpg

Ivy (Hedera spp.) is the most common invasive plant in Lake Oswego and the biggest threat to urban forest health and sustainability. It is an aggressive species with no natural enemies that grows and reproduces quickly, outcompetes native plants like wildflowers and ferns, and can rapidly grow up tree trunks with detrimental effects. Ivy competes with trees for water and nutrients, deprives tree bark of normal contact with air and microorganisms, can completely overgrow and kill trees, and the weight of ivy increases susceptibility to wind stress and the risk of branch or whole tree failure.

Ivy is easy to identify by its waxy evergreen leaves. It is a woody vine with a shallow mat-like root system that is a poor choice for erosion control. Ivy is commonly found growing along the ground, up trees, and on walls or other obstacles. Ivy tolerates drought, frost and deep shade, but climbs trees and other tall objects to access sunlight using modified roots to adhere to its host. Flowers and berries produced in late fall and early winter turn to seed in the spring and spread by birds, but ivy also reproduces from rootlike stems and sprouting fragments.

Manual removal of ivy is labor intensive, but the most effective means of control. When manually removing ivy, it is critical to remove as much ivy stem and root as possible because of its ability to regenerate. At the same time, try to minimize soil disturbance and protect desirable plants. Wear gloves and long sleeves as the sap is known to cause a reaction in some people.

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 6-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 ivy and how to remove it by visiting these sites:

• Why is Ivy a Problem? Oswego Lake Watershed Council webpage
• Ivy Removal in a Home Landscape, Oregon State University Extension Service webpage
• English Ivy Management Resource Packet, Oregon Department of Agriculture
• English Ivy, King County Noxious Weed Alert
• ​Video: How to Remove Ivy, West Multnomah Soil and Water Conservation District

Seasonal Tree Care Tips: Winter 2024
Clean and Sharp Pruners

Bypass Pruners.jpg

PHOTOGRAPH CREDIT: Proper orientation of pruners, with cutting blade closest to remaining part of branch or stem. Source: Joseph OBrien, USDA Forest Service, Bugwood.org

When practicing pruning, clean, sharp, well-maintained tools work best. Over time, tools deteriorate from dampness, sap, soil and rust. It’s important to store your tools in a clean and dry place when not in use. Periodically cleaning and sharpening your tools will help keep them in good working condition for many years to come. Resources provided at the end of this article include tips for maintaining a variety of common gardening tools including loppers, shears, shovels, hoes, axes and hay forks, but this article focuses on cleaning and sharpening bypass blade hand pruners, our favorite and most-used tool for pruning small tree branches and shrubs.

Bypass-blade hand pruners are ideal for pruning small branches because they are hand-held and make accurate pruning cuts when used properly. Bypass pruners come in a variety of sizes, but all have two blades that “bypass” each other, with only one sharp blade, which results in a smooth, clean cut. A dull and rusty blade makes the job harder and results in jagged or torn cuts that take longer to heal. Sharp and sterile bypass pruners will make the job easier and help ensure proper cuts can be made to reduce the risk of decay and disease in pruning wounds. Thoroughly clean and then sharpen your bypass pruners at least once a year, or more often if you’re a frequent pruner. If pruning trees or shrubs with known disease, clean your tools with household cleaner or rubbing alcohol after each use, prior to moving on to another plant.

Even a dull blade can cause serious injury, so be sure to take your time and work in a safe manner throughout each step of the cleaning and sharpening process!

Supplies needed to clean and sharpen pruners:

• Safety Glasses   
• Wrench
• Rags
• Household cleaner or rubbing alcohol
• Scrubbing pad
• Steel wool
• WD-40 or other solvent
• Diamond File (fine or medium coarse)
• Tool oil

Instructions to clean and sharpen pruners:

1. Disassemble: Take a photograph of your pruners before disassembly to refer to later, if needed. Use a wrench to remove the bolt(s) and look for small parts like washers and nuts. Lay each of the pieces out in order for easy reassembly later. 
2. Clean: Use hot soapy water and a rag to clean the blades. Household cleaner or rubbing alcohol may be helpful to remove sap and other buildup, along with a scrubbing pad. Use WD-40 or other solvent and steel wool to remove rust. Once the surface is smooth, rinse the blades with water and thoroughly dry them off.
3. Sharpen the Cutting Edge: Put on your safety glasses. Find the angled (beveled) edge of the pruners, this is the only side of the blade you should sharpen; never file the flat side. With a firm grip on the file handle, apply light pressure and push the file across the blade in one direction matching the beveled angle. Do not file back and forth like a saw, just move in one direction making smooth strokes until the entire beveled edge is shiny and free of nicks. Filing doesn’t take much effort, but be patient and maintain control.
4. Reassemble and Test: Reassemble the pruners, referring to the photograph you took in step 1 for assistance. Make sure the bolt(s) are snug, but not overtightened. Cut a piece of paper to test the sharpened blade; a clean cut means the blade is sufficiently sharp.   
5. Oil: Use a clean rag to apply a very light coating of tool oil to the moving metal parts. This will lubricate the moving parts and help prevent rust. Wipe off any excess oil with the rag.

Visit these sites for more information on cleaning and sharpening a variety of garden tools, selecting the right tool for the task, and proper pruning practices:

How to Sharpen Your Pruners, a UNH Extension Education Center YouTube video with step-by-step instructions 
How to Maintain Bypass Pruners, an Ask This Old House YouTube video 
Sharpening Garden Tools, OSU Master Gardner Association – Clackamas County Chapter, in cooperation with OSU Extension Services 
Care and Maintenance of Garden Tools, OSU Master Gardner Association – Clackamas County Chapter, in cooperation with OSU Extension Services 
Pruning with the Pros – Tools of the Trade, OSU Extension Service video on a selection of tools that are needed for proper mature tree pruning in the landscape
Pruning Young Trees, International Society of Arboriculture 
Pruning Mature Trees, International Society of Arboriculture 
Tree Owner’s Manual, USDA Forest Service, Northeastern Area, State and Private Forestry, NA-FR-04-07, November 2008 (see pages 18-23) 

 

Seasonal Tree Care Tips: Fall 2023
Mediterranean Oak Borer

Photo Credits: Female Mediterranean Oak Borer, just 1/10th of an inch long. Photo by Curtis Ewing, CAL Fire. Source: ODF MOB Fact Sheet. Pale colored boring dust along the trunk of an Oregon white oak. Photo by Morgan Holen, 2023.

A new pest is raising concern for oak trees in Oregon. Mediterranean oak borer (Xyleborus monographus), or MOB, is an invasive insect from Europe, the Middle East and northern Africa that primarily infests weak or dying trees of a variety of oak species. This tiny woodboring beetle is a type of ambrosia beetle that eats fungus grown in galleries created in the wood of branches and tree trunks. Some fungal species may cause a disease called oak wilt that can kill trees within as little as two years. While common native ambrosia beetles infest dead or dying trees, MOB attacks live, mature trees.

Our neighbors to the south in Wilsonville witnessed rapid decline of several very large Oregon white oaks, prompting an investigation that led to confirmation of MOB.

MOB was first discovered in the United States in California in 2017. Here in Oregon, MOB was first found in a single trap set by Oregon Department of Forestry (ODF) in Multnomah County in 2018. In 2020, MOB was found in traps in Marion County, then in Clackamas and Washington counties in 2021 and 2022. In the spring of 2023, MOB was found in a single Oregon white oak at Sandy River Delta. Since then, MOB has been confirmed in more than a dozen Oregon white oaks in the City of Wilsonville.

Upon confirmation of MOB in Wilsonville, the City immediately began collaborating with the Oregon Department of Agriculture (ODA), ODF, Metro and the City's consulting arborists to identify and mitigate MOB’s presence, survey and assess symptomatic trees, and develop management strategies to help local jurisdictions.

Early detection is vital to preventing the spread of MOB. Learn how to identify oak species, review the signs and symptoms of MOB, and report oaks with both crown dieback and any of the symptoms below to the Oregon Invasive Species Hotline at: https://oregoninvasiveshotline.org/login/?next=/reports/detail/2018.

Signs and Symptoms of MOB Infestation:

1. Individual branch death in the top third of the tree.
2. Very small and perfectly round entrance and exit holes about 1/16” (1.3-1.5mm) in diameter.
3. Fine white or pale colored boring dust, almost sand-like in appearance, on the exterior of the tree trunk or in mounds along branches.
4. Black branched trellises, tunnels or galleries 1.2-1.5mm in diameter on the interior cut face of wood.
5. Tiny reddish-brown beetles about 1/10” (2.3-3.1mm) long.

Symptoms Not from MOB include:

• Discolored leaves but absence of branch dieback;
• Holes larger than the diameter of a pencil lead;
• Brown boring dust;
• Wood staining without associated galleries.

In the meantime, ODA and ODF are asking people not to move firewood from oak trees beyond the local area where it is cut to avoid spreading the insect pest, and, be sure to inspect wood from oak trees that are pruned or removed for signs of MOB before hauling it away. If signs of MOB are suspected, cover the wood with a tarp and contact ODA through the Oregon Invasive Species Hotline. Infested trees and wood should be safely burned, heat treated, finely chipped or deep buried.

Visit these sites for more information:

ODF MOB Fact Sheet: https://tinyurl.com/MOB-oregon
ODA MOB Fact Sheet: https://www.oregon.gov/oda/shared/Documents/Publications/IPPM/MediterraneanOakBorerAlert.pdf
Common Trees of the Pacific Northwest: https://treespnw.forestry.oregonstate.edu/broadleaf_genera/species/oak_spp.htm
City of Wilsonville MOB Resources: https://www.ci.wilsonville.or.us/natural/page/mediterranean-oak-borer
Don’t Move Firewood: https://www.dontmovefirewood.org/map/oregon

 

Seasonal Tree Care Tips: Summer 2023
Supplemental Watering and Mulch to Prevent Drought Stress in Trees

Photo Credit: Screen shot taken from Watering Mature Trees, a YouTube Video by the US Forest Service, showing how to properly place a soaker hose around a tree to provide supplemental watering. 

Extended periods of hot and dry weather 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. Don’t wait until it is too late! Follow these helpful tips to ensure you are watering efficiently and effectively.

Before watering, test the soil to confirm that it is dry. Stick a long (8”+) screwdriver into the ground near the outer edge of the tree’s canopy. If it comes up with little to no dry soil stuck to it, the soil is dry.

For both young and mature trees, an infrequent, slow and deep soak is better than watering a little every day. A slow, deep soak promotes deeper root growth and overall health by ensuring that roots are receiving the water. A soaker hose can be placed on the ground surface beneath the tree’s canopy either in a spiral or zig-zag arrangement. Applying water directly to the soil helps to minimize water loss due to evaporation. Avoid watering at the base of the trunk to prevent decay.

Turn the soaker hose on in the evening, or early morning, and leave it on for at least one hour or longer depending on the size of your tree. Young trees generally need 15 to 20 gallons of water once a week, while mature trees need anywhere from 20 to 50 gallons a month depending on size. If you have a very large mature tree, you may need to leave the soaker hose on for several hours depending on the type of soaker hose you use and your water pressures. Overwatering can be equally detrimental, so check the soil periodically to make sure the water flow is slow and deeply penetrating the soil. Only provide supplemental watering during the hottest and driest times of the year, generally July and August, but sometimes in June and September, too. This year, young trees likely needed a soak in May. 

An easy alternative to a soaker hose involves drilling three small 3/16-inch holes into the bottom of a 5-gallon bucket. Place the bucket beneath the tree’s canopy (and closer to the trunk, but not right up against it, for young trees that are still establishing, up to three years old). Fill the bucket with water for a slow, deep soak during the hottest and driest times of the year. One 5-gallon bucket will need to be refilled three to 10 times to fully water a tree, depending on its size. Move the bucket around beneath the canopy each time you refill it and feel free to use more than one bucket at a time, just keep track of how many times you refill the buckets. Repeat this process monthly when the soil is dry, and more often for young trees.

Set a calendar reminder sometime near the last week in July and the last week in August to remember to check the soil, and keep in mind, that when the soil is dry, a slow and deep watering is only needed once a week for young trees and about once a month for mature trees.

In addition to supplemental watering, maintain a grass-free mulch ring around your trees. A 2- to 4-inch layer of bark mulch helps to retain soil moisture and moderate soil temperature. Just be sure to avoid piling mulch against the trunk around the base of the tree and don’t exceed the recommended 2- to 4-inch depth.

Visit these sites to learn more:

• Watering Mature Trees, a YouTube Video by the US Forest Service 
• Watering Your Trees, an Oregon Department of Forestry Forest Benefits Fact Sheet 
• Drought Stress, an article by The Morton Arboretum  

 

 

Seasonal Tree Care Tips: Spring 2023
Aphids

Tuliptree Aphids and Ladybug - Credit Lacy L. Hyche, Auburn University, Bugwood.org_.jpg

Photo Credit: These aphids are feeding on a tuliptree leaf, but the ladybug is a natural predator. Both ladybug adults and their larvae feed on insects, including up to 50 aphids a day. Credit: Lacy L. Hyche, Auburn University, Bugwood.org

Aphids are perhaps the most common insect pest that you’ll encounter. They are present year-round and attack a wide variety of garden and landscape plants, but especially love tender young plant growth in the spring. There are over 4,000 species of aphids in all different sizes, shapes and colors. Some are woolly, some have wings, but they are all tiny, soft-bodied insects with needle-like piercing and sucking mouth parts that feast on plant juices.

 

Certain vegetables and ornamental plants are susceptible to serious aphid damage and aphids may transmit viruses from plant to plant, but aphids seldom kill mature plants and are not serious threats to trees. Though dense populations can suck enough sap to reduce vigor, cause leaves to curl or become spotty, and deform flower buds, it’s typically the sweet sticky honeydew aphids leave behind that is the biggest nuisance. Honeydew is a food source for ants, bees and flies, but also encourages sooty mold to grow, which is not only unattractive, but can reduce photosynthesis and flower production.

 

Aphids most often feed in dense groups and don’t move rapidly when disturbed. While most aphids feed on leaves and shoots, several species of aphids feed on stems, flowers, buds, or bark or root tissues of trees. Some tree species particularly susceptible to aphids include aspens, beeches, birches, cottonwoods, elms, hawthorns, lindens, Norway maples, spruces, tuliptrees, walnuts, willows, and fruit trees.

 

Aphid Life Cycle

The aphid life cycle is pretty fascinating. Female aphids can actually carry multicellular embryos of their granddaughters, further accelerating reproduction and population growth. That’s right, female aphids can be born already carrying embryos of the next generation.

In the fall and winter, female aphids mate with male aphids and lay eggs, but throughout the summer months adult females can give birth to live female offspring without mating and each offspring may already be carrying the next generation. Adult aphids are able to simultaneously feed and reproduce, often as many as 12 offspring a day. There is no pupal stage and aphid newborns begin to feed right away. The young nymphs molt and shed their skin about four times before becoming reproductive adults within about eight days. Each female aphid lives about one month, producing 60 to 100 nymphs over 20 to 30 days.

Both nymphs and adults pierce plant parts and suck on the phloem to feed. Aphids require nitrogen for growth and development, but phloem sap is relatively poor in nitrogen and high in carbohydrates. Aphids must consume large volumes of sap to extract sufficient nitrogen and all that excess residue is extracted as sticky honeydew.

 

Management Tips

• Keep your plants healthy with adequate sunlight, water and nutrients to fend off aphids more easily than stressed plants. In your vegetable garden, use row covers to protect young plants from aphid infestation.
• Dial back on fertilizers.  If you must use fertilizer, use slow release or organic fertilizers to avoid overdosing the plant so that aphids are not bolstered by rapid succulent new growth and avoid high levels of nitrogen which favor aphid reproduction.
• Monitor your plants at least twice a week when plants are growing rapidly to catch infestations early so you can knock them out or hose them off.
• Managing ants is a key component of managing aphids. While ants feast on the honeydew aphids excrete, they also act as bodyguards, defending aphids from natural predators such as ladybugs and parasitic wasps. Sticky traps, ant stakes and containerized baits can be used to control ants, allowing aphid predators easy access.
• Don’t plant aphid-attracting plants where honeydew will be most problematic, like near a parking area or deck.

 

Treatment Options

• Biological. Incorporate plants into your landscape, such as yarrow, wild buckwheat, and caraway, that will attract and foster natural predators. If you create good habitat, but just can’t wait for aphid enemies to move in, you could try introducing them—both ladybugs and green lacewings are sometimes available for purchase. However, adult ladybugs commonly just fly away when released, so opt for green lacewing eggs and larvae at your garden center, if possible.
• Mechanical. Small populations can be treated simply by hosing them off the plant with a strong stream of water. Be sure to blast the underside of leaves where aphids are most common. Repeat this every few days until you find the population is nearly gone. Badly damaged foliage can be pruned off.
• Chemical. Insecticidal soaps are the least toxic method of chemical control and are available at most garden stores. Mix the solution and apply in accordance with the manufacturer’s label and spray the soap solution directly on the aphids to eliminate them. The spray is only effective if it comes into direct contact with the pests, and beneficial predatory insects with hard bodies are not affected. Commercial formulations have been widely tested and are said to be safer than homemade solutions. To avoid plant damage, be careful not to mix at too strong of a rate (follow the label directions), test spray a few leaves several days in advance of full treatment and inspect for browned or burnt plant tissue, and avoid such treatments on hot sunny days.

​Visit these sites to learn more:

• Aphids, How to Manage Pests in Gardens and Landscapes.
• Common Landscape Pests – Aphid.
• How to Control Aphids with Less Toxic Methods, Oregon State University Extension Service.
• Spring’s Earliest Pests: Aphids Jean R. Natter, OSU Extension Service Master Gardener.
• A Sweeter Side of Aphids, Bug of the Week, Michael J. Raupp, Ph.D., Professor of Entomology, Extension Specialist, University of Maryland.
• Aphids and Their Bodyguards, Bug of the Week, Michael J. Raupp, Ph.D., Professor of Entomology, Extension Specialist, University of Maryland.
• Foolproof Aphid Control and Prevention, Epic Gardening. 

Seasonal Tree Care Tips: Winter 2023

Pruning: Standards and Best Practices

To prune, or not to prune, that is the question. Well-trained arborists often say that every pruning cut should have a purpose, such as reducing the risk of branch failure, providing clearance, maintaining health, influencing flower or fruit production, and improving aesthetics.

Without good reason, removal of more than 25% of the live crown in a single-year is generally not acceptable, but common exceptions include hazard reduction and storm damage repair. Removal of 50% or more of the live crown in a single year can lead to decline in tree health due to energy reserves being depleted and a reduced ability to photosynthesize. Over pruning may also diminish a tree’s structure and make it more susceptible to failure. Lake Oswego Code, Chapter 55, prohibits topping as well as the removal of 50% or more of a tree’s crown. The City does occasionally issue topping permits to utility companies for public safety, though topping is generally considered an unacceptable practice and pruning for the objective of utility line clearance is not discussed in this article.

Common types of pruning to meet the defined objectives include:

• Structural pruning to influence orientation, spacing, growth rate, strength of attachment, and the ultimate size of branches and stems;
• Cleaning to selectively remove dead, diseased and broken branches;
• Thinning to selectively reduce the density of live branches;
• Raising, also known as lifting, to provide vertical clearance;
• Reducing, also known as reduction pruning, to decrease branch height or length; and,
• Restoring, a process of improving the structure of a tree that was previously damaged.

ANSI A300, The American National Standard for Tree Care Operations—Tree, Shrub, and Other Woody Plant Maintenance—Standard Practices, is the tree care industry standard of care in the USA. International Society of Arboriculture (ISA) Best Management Practices for Pruning aids in the interpretation and implementation of ANSI A300. When these standards and practices are followed, every pruning cut has a purpose.

How to prune is an entirely different question and proper pruning is usually best left to the experts, particularly for large and well-established trees that may only be accessible by climbing or using a lift. A comprehensive pruning proposal from a qualified tree service company should always include written specifications based on the need for pruning and the condition and size of the tree to be pruned. Here is what to look for:

• Does the proposal clearly identify which trees are to be pruned?
• Are the pruning objectives defined?
• Does the proposal describe the pruning types to be performed?
• Are the minimum and maximum size range of branches to be removed specified?
• Does the proposal specify a maximum percentage of live tree canopy that can be removed?
• Is there a statement that all work shall be performed in accordance with the ANSI A300 pruning standard and ANSI Z133.1 safety standard?

When it comes to pruning shrubs and small trees, you might enjoy getting outside, cleaning and sharpening your tools, and having a conversation with your plant to define the objectives and practice your pruning skills. If this sounds like fun, be on the lookout for the City’s annual Tree Pruning Workshop this spring and submit your free registration early as it tends to fill up fast!

Visit the archives to learn more about tree care after storm events (spring 2021) and structural pruning for young tree establishment (spring 2018). Please check back quarterly for more tree care and maintenance advice!

References:

Gilman, E.F. and Lilly, S.J. (2002) Best Management Practices, Tree Pruning. Champaign, IL: International Society of Arboriculture.

 

 

Seasonal Tree Care Tips: Summer 2022
Emerald Ash Borer

EAB Feeding on leaf.jpg

Close-up of an adult female emerald ash borer feeding on an ash leaf; length ranges from 0.33 to 0.53 inches, that’s smaller than a penny. Credit: Leah Bauer, USDA Forest Service Northern Research Station, Bugwood.org

Emerald ash borer (EAB), an invasive beetle that infests ash trees, was discovered in Forest Grove, Oregon, on June 30, 2022. This is the first time EAB has been identified in Oregon, but the state has been preparing for its arrival for years.

EAB was first discovered in the United States in Michigan in 2002, likely arriving in wood packing materials from Asia. This metallic wood-boring beetle threatens all species of ash tree (Fraxinus genus) and is considered the most destructive forest pest ever seen in North America with the potential to create billions of dollars in damages nationwide. EAB has killed hundreds of millions of ash trees across the east coast and Midwest over the last 20 years. Here in Oregon, loss of our native ash tree, Oregon ash (Fraxinus latifolia), a very important riparian and wetland species west of the Cascades, is of grave concern, as well as the loss of widely planted non-native and cultivated ash trees in urban landscapes.

Unfortunately, there are no effective means of eradicating EAB, but here’s what you can do to help:

Be on the lookout for EAB. Learn to identify ash trees and EAB (there are many look-alikes), and report suspected sightings immediately.
 
Don’t actively plant ash trees, but take good care of the ash trees you have. This includes providing supplemental water during summer heatwaves, treating high-value ash trees with systemic insecticides, and removing dead and dying ash trees and replanting with another species suitable for the specific site conditions. A qualified and experienced plant health care specialist can prescribe and implement appropriate treatments.
 
Don’t move firewood and be sure to dispose of ash wood properly.
 
Learn more about EAB by visiting these resources:

• Forest Facts: Emerald Ash Borer (EAB) Agrilius planipennis Fairmaire, a publication of the Oregon Department of Forestry
• EAB Look-Alikes, a publication of the Oregon Department of Agriculture
• Learn how to identify ash trees
• Get the latest news on EAB from the Oregon Department of Forestry
• Oregon dad spots the first emerald ash borers on the West Coast during summer camp pickup in Forest Grove, Press Release, July 12, 2022
• Destructive bug could wipe out ash trees, a KOIN News segment featuring ODF Forest Entomologist Christine Buhl, July 26, 2022
• Report Suspected Sightings to the Oregon Invasive Species Council 

Seasonal Tree Care Tips: Winter 2022
Nesting Season

Birds nest in a wide variety of places including tree branches, cavities, logs and stumps, on the ground, under shrubs, in open gravel, along stream banks, in chimneys, on bridges, ledges and light poles, and under the eaves of your house. Activities that threaten nesting birds are not limited to tree removal and pruning; mowing your lawn, clearing invasive or native vegetation from the ground, grading and building, or applying herbicides are all potentially disruptive.

The Migratory Bird Treaty Act (MBTA) of 1918 provides protection to all native bird species, even native species that are non-migratory. There are over 200 native bird species in the Portland area, including common species like robins and song sparrows, and less common species like flycatchers and bushtits. This Federal law, administered by the United States Fish and Wildlife Service (USFWS), makes it illegal to hunt, pursue, wound, kill, possess, or transport any native bird, their eggs, feathers, or nests, either intentionally or accidentally, without a permit from USFWS.

Nests are only protected when they are active, meaning when they contain eggs or young. Once fledglings have left the nest, the nest is no longer protected by law. In general, nesting season in our region is divided into three timeframes:

August 1 – January 31 is the non-breeding season and the best time for site disturbing activities.
February 1 – April 14 is early nesting season, a time to be aware of potential impacts and survey areas for active nests before conducting potentially disruptive activities.
April 15 – July 31 is primary nesting season, a time to avoid disturbance if at all possible and survey sites for active nests when potentially disrupting activities are unavoidable.

The City of Lake Oswego does not have authority to administer or enforce the Federal MBTA, but we all have a responsibility to avoid active nests and delay potentially disturbing activities until birds have fledged. Most birds will leave the nest within about two weeks.

Visit these resources to learn more about the MBTA, what to do if you find a baby bird out of its nest, landscaping for native bird habitat, and more:

Bird Conservation History, A Timeline of Important Dates in the Conservation of Migratory Birds, United States Fish and Wildlife Service
Current list of MBTA protected species
Living with Wildlife, information on how to live with wildlife provided by the Oregon Department of Fish and Wildlife, Wildlife Division 
Be on the Lookout for Nesting Birds: Springtime is Hatching Time, an April 2020 news release from the Oregon Department of Fish and Wildlife 
Protecting Nesting Birds, Best Management Practices for Vegetation and Construction Projects, Version 3.0, May 2017, City of Portland, Bureau of Environmental Services

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:

Can These Trees Be Saved? 
Tree First Aid After a Storm. 
Reducing Tree Damage in Future Storms

Tree City USA Bulletins by the Arbor Day Foundation:

When a Storm Strikes 
How to Make Trees Storm Resistant 
Do Your Trees Pose a Risk? 

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. 

Tree Pruning

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.

Tree removal application forms are at the following link: Permit Types, Requirements, and Applications | City of Lake Oswego. Submit the completed application to trees@lakeoswego.city.

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:

Why Hire an Arborist, a brochure from the International Society of Arboriculture

Homeowner Resources:

Find an Arborist  (Tip! Search within 25 miles of your postal code for a more extensive listing) 
Verify an Arborist’s ISA Credentials 
Find a Consulting Arborist
Find a TCIA Tree Care Company

Seasonal Tree Care Tips: Fall 2020
Soil Management  

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 trees@ci.oswego.or.us 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 planning@lakeoswego.city 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

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
Summer 2018

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:

Don’t Move Firewood

Identify Invasive Pests

Oregon Forest Pest Detectors 

EAB Readiness and Response Plan for Oregon 

To report a suspected invasive species, visit oregoninvasiveshotline.org or call 1-866-INVADER.

Pruning Young Trees
Spring, 2018

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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:

Brochure – Pruning Young Trees by the International Society of Arboriculture

Webpage – Annual Tree Pruning Steps from Planting to Maturity by the Arbor Day Foundation

Video – Training Young Trees by Larry Costello and Ellyn Shea

 

 

Tree Related Storm Damage
Winter, 2018 

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:

Video – Tree Care Tips: Storm Damage and Trees by Stihl USA

Brochure – Weathering the Storm: Safe Response to Tree-Related Storm Damage by the International Society of Arboriculture

 

Fall, 2017

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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:

iOS and Android App: A New Tree by Oregon State University
Species Guide: Right Tree in the Right Place
Video: How to Plant a Tree Properly

 

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Summer, 2017

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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Spring, 2017

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:

Cabling & Bracing Trees as a Corrective Measure

Mulching Trees & Shrubs

A Guide to Collecting Soil Samples

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FALL, 2016

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.