Post: October 17, 2025

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Conifers in the Homescape

Selecting and caring for conifers will provide year-round beauty and function

By Alison Hitchcock, Skagit County WSU Extension Master Gardener

Conifers make a valuable addition to any garden, providing a variety of landscape uses: hedging, windbreaks, ground covers, or specimen focal points. They provide year-round color, texture, and a range of appealing attributes. Once established, conifers require very little care, rarely need fertilizer, resist most insects and diseases, and pruning becomes an optional task.

The term conifer is derived from the Latin words “con” and “ferre, referring to the cone, and the term “to bear”. Broadleaved trees such as holly, laurel, or eucalyptus reproduce with flowers and fruits; conifers reproduce through cones. Both pollen (male) and seed (female) cones are formed; all are wind-fertilized. Most conifers are monecious (Greek, one house) with male and female cones occurring on the same tree, but several genera are diecious (two houses). The age at which a conifer bears cones varies, but it usually takes at least 10 years before cones appear. Maturation can vary from 1 to 3 years. Some dwarf varieties never develop cones.

 

Know & Grow Series:

Conifers in the Home Landscape

Free, no registration required
Listen to Master Gardener Alison Hitchcock speak on caring for conifers in the home garden. Alison Hitchcock has been a Skagit County WSU Extension Master Gardener since 2001. Prior to retirement, she worked for the Department of Natural Resources as the Northwest Regional Silviculturist.

Tuesday, October 21, 2025 – 1 pm – 2:30 pm

NWREC Sakuma Auditorium, 16650 State Highway 536, Mount Vernon

While the majority of conifers are considered evergreen (foliage retained more than one growing season), there is a small group of conifers: larch, bald cypress, and dawn redwood that lose their needles every year, i.e., deciduous. Despite the term, conifers do not keep all their leaves indefinitely. Needles become less efficient as they age, accumulate surface debris, and receive lower levels of sunlight due to interior foliage. These unproductive leaves are shed over time, though the needle life span will vary by species. Pines rapidly shed needles every 3-4 years; spruce and fir needles turn yellow and drop gradually; yews turn yellow and drop in the late spring or early summer of their third year. Sequoias, redwoods, and arborvitae shed small branchlets. We witness the flagging of western red cedar each autumn as older foliage dies.

 

Tree and Site Selection
When selecting a conifer, there are several things to consider: function, size and space needs, sunlight, and soil needs. Numerous cultivars of all shapes and sizes are available from local nurseries and garden centers to meet the needs of your garden design.

 

Selected Conifer Names
Family	Genus	Common Name
Cupressaceae	Thuja	red cedar (arborvitae)
Cupressaceae	Cupressus	cypress
Cupressaceae	Chamaecyparis	false-cypress
Cupressaceae	Colocedrus	incense-cedar
Cupressaceae	Juniperus	juniper
Cupressaceae	Sequoia	coast redwood
Cupressaceae	Sequoiadendron	giant sequoia
Cupressaceae	Metasequoia	dawn redwood
Cupressaceae	Cryptomeria	Japanese cedar
Cupressaceae	Taxodium	bald cypress
Taxaceae	Taxus	yew
Taxaceae	Cephalotaxus	plum yew
Pinaceae	Thuja	red cedar (arborvitae)
Pinaceae	Larix	larch
Pinaceae	Cedrus	true cedar
Pinaceae	Pinus	pine
Pinaceae	Tsuga	hemlock
Pinaceae	Pseudotsuga	Douglas fir
Pinaceae	Ablies	true fir
Pinaceae	Picea	spruce
Scadopitaceae	Sciadopitys	umbrella pine
Araucariaceae	Aracucaria	monkey puzzle
Araucariaceae	Wollemia	Wollemi
Podocarpaceae	Podocarpus	podocarp yew

A cultivar represents a deviation from normal characteristics common to a species. Though some cultivars are the result of human hybridization, most cultivars arise from mutations that give rise to dwarf and giant forms, variegated foliage, weeping, and prostate habits. If the unique traits are maintained over multiple generations, plant biologists can give a cultivar a new name and propagate it through grafts and cuttings.

 

When selecting a conifer, one must anticipate the tree’s mature size and space needs. The American Conifer Society has established four size categories for conifers: Miniature, Dwarf, Intermediate, and Large, to aid in landscape design. Once established, growth may vary slightly due to local environmental conditions, but registered cultivars should maintain their described size. It is essential to note that any conifer will continue to increase in size at the stated rate beyond 10 years. If your tree becomes too large, corrective measures are limited to perpetual pruning, relocation, or removal. In most cases, severe pruning will destroy the conifer’s natural charm, although some plants may recover over time. Often, removing and replacing a large tree is easier, although removal can be costly.

 

Shade Tolerance of Selected Conifers

Tolerant Hemlock Yew Western red cedar Redwood Chamaecyparis Sitka spruce Intermediate Douglas-fir Sequoia Blue spruce

Intolerant Pine Juniper Noble fir Very Intolerant Larch

Shade and soil conditions can be particularly important when selecting the right conifer. Shade-tolerant species are able to thrive and reproduce under low light levels, while intolerant species require full sunlight and little or no competition. Most conifers prefer full sun and evenly moist, well-drained, neutral to acid soil. The few species that tolerate wet soils include Atlantic white cedar, dawn redwood, and some spruces. Drought-tolerant species include juniper, cypress, and pine.

 

Pruning and Shearing
The pruning needs of conifers are minimal if plants are chosen to fit their allotted space. Always prune a conifer for a particular purpose: removal of diseased or dead wood, control of size, and control of shape. Though the techniques sound similar, there are essential differences between pruning and shearing. Pruning refers to the selective removal of branches for the health and proper size of a plant. Shearing removes foliage to create a uniform surface or shape without regard to branch structure. Pruning cuts encourage growth throughout the plant, while shearing is generally limited to the current year’s growth.

 

Pruning of Douglas fir leader. Developing Quality Christmas Trees in the Pacific Northwest © Oregon State University Extension | Chad Landgren

 

Pruning Whorl-branched Conifers
(Douglas fir, spruce, true fir, true cedar, pine)

Whorl-branched trees will not form new buds on old wood, so do not cut back to the brown, aged stems. To control height or branch length, always cut back to a side branch or dormant bud. Pruning the outermost branch tips back to a bud will also encourage fullness. For a formal shape, shear in summer after new growth has expanded but before new buds form in the fall. To replace a lost leader, support the uppermost lateral branch to a vertical position with a splint and remove after one growing season.

Unlike other whorl-branched conifers, a pine’s current year’s shoots (candles) should be pruned in late spring. To slow growth or produce a more compact shape, pinch one-third to one-half of each candle; to maintain size, remove most of each candle. Shearing is not recommended for pines.

Pruning Random-Branched Conifers
(Juniper, Arborvitae, Chamaecyparis, yew, hemlock)

Pruning to maintain shape is best done in early spring so that new growth covers the cut ends. Snip branch tips back lightly. Hand pruning rather than shearing creates a more natural shape, but plants can be sheared in early summer once the tree stops growing.

Yew and hemlock are exceptions to most conifers in that new growth will develop on old wood, and they are forgiving of poor pruning and very suitable for hedging. To maintain size, prune in late winter or early spring before new growth begins. Avoid trimming the tops of hedges until the desired height has been reached. If shaping for fullness or a formal hedge, lightly trim back the outermost new growth using hand pruners or hedge shears. Shearing of new growth can continue into early summer.

Incorporating conifers into your garden design not only enhances visual interest but also promotes a resilient landscape with minimal upkeep. By carefully considering their size, light, and soil requirements these remarkable plants can thrive in your garden. Whether used as hedges, focal points, or ground covers, conifers will provide lasting beauty and functionality to your outdoor space. 

When to prune or shear is mainly dependent on conifer branching patterns, either whorl-branched or random-branched. Whorl-branched (determinate) conifers put on one flush of growth each spring. Buds at the tips of the tree flush in the spring, elongate until sometime in July, and then set new buds in the fall for the following spring. Random-branched (indeterminate) conifers produce new growth from buds at the tips of the branches and from dormant buds further back on the stem than the whorled-branched species. The result is that random-branched conifers can be cut back more severely and still produce new growth.

General guidelines for pruning:

• Remove dead, diseased, or broken branches anytime.
• Prune all conifers, except pine, before new growth starts in the spring or during the semi-dormant period in mid-summer after growth has stopped.
• If shearing, begin in late spring or early summer after new growth begins.
• Do not prune evergreens in late summer or early fall; new growth will not harden off and will be subject to winter injury.
• Do not prune into the inactive center because new branches will not form to conceal the stubs.
• For prostrate or open-grown trees, selectively prune individual branches rather than shearing the whole plant.

Resources and References:

American Conifer Society, accessed April 25, 2025, 

Welch, H., (1966) Dwarf Conifers – A Complete Guide. Charles T. Branford Company, Newton, Massachusetts

Landgren, C. (2025) Developing Quality Christmas Trees in the Pacific Northwest, Oregon State University Extension. 

Bird, R. (1994) Ornamental Conifers. Quintet Publishing Limited, London, UK.

Hartman, J., Pirone, T., and Sall, M. (2000) Pirone’s Tree Maintenance. 2000. Oxford University Press, New York, NY.

ABOUT THE AUTHOR:
Alison Hitchcock has been a Skagit County WSU Extension Master Gardener since 2001. Prior to retirement, Alison worked for the Department of Natural Resources as the Northwest Regional Silviculturist.

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Questions about home gardening or becoming a master gardener may be directed to Skagit County WSU Extension Office, 11768 Westar Lane, Suite A, Burlington, WA 98233; by phone: 360-428-4270; or via the Skagit County WSU Extension website.

Washington State University Extension helps people develop leadership skills and use research-based knowledge to improve economic status and quality of life. Cooperating agencies: Washington State University, US Department of Agriculture, and Skagit County. Extension programs and policies are available to all without discrimination. To request disability accommodations contact us at least ten days in advance.

Posted August 1, 2025

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The Vital Role of Trees in Our Ecosystem and Well-Being

By Kathy Wolfe, Skagit County WSU Extension Master Gardener

Kathy Wolfe

Imagine for a moment that you are in a woodland. Every shade of green, from the deepest emerald to the lightest celadon, is represented in the surrounding landscape. The air is filled with scents from tree oils and the earth: cedary bark, musty decaying wood, leafy freshness. Overhead boughs scratch and moan as the wind blows through the canopy. A squirrel scampers across the forest floor, and birds sing overhead. Your step slows. Your breath softens. This is the feeling the Japanese describe as “forest bathing.” Being in the company of trees is said to reduce stress, boost the immune system, and improve your overall feeling of well-being. This is but one benefit of having trees in our lives.

Humans have revered trees in religions and cultures throughout time. European Druids worshiped oak trees, believing them to be a connection between the earth and spiritual worlds. The Native American cultures often viewed trees as sacred and integral in their spiritual and cultural lives and as sentient community members that lived among them. African Baobabs are known as the “Tree of Life” and symbolize resilience and humility. Many Asian cultures have sacred trees, including the Bodhi tree, where Buddha is said to have achieved enlightenment, the Kalpavriksha in Hindu culture, which is believed to grant wishes, and the shinboku, which are often planted near shrines in Japan.

Used with permission © Crowell Photography

Used with permission © Crowell Photography

Science has proven the functional benefits of trees as well.
Here are some examples:

Removing pollutants from the atmosphere.
Tree leaves filter dangerous particulate matter that comes from burning fossil fuels by intercepting the particles on plant surfaces. Gaseous pollutants are absorbed through the leaf stomata, which are tiny pores on leaf surfaces. Gases like ozone, carbon monoxide, nitrogen dioxide, and sulfur dioxide can be diffused into the intercellular spaces within the leaf. Some can also be metabolized or broken down by plant enzymes.
Mitigating climate change by storing carbon.
Trees absorb carbon dioxide from the air through photosynthesis and store it in their wood during the lifetime of the tree, helping slow gas build up in our atmosphere. Using sunlight, trees convert carbon dioxide and water into sugars for energy and release oxygen as a byproduct. Older, larger trees store more carbon than young trees, making it important to conserve and protect old-growth forests as well as plant new trees.
Managing stormwater runoff and erosion.
Flash flooding can cause immeasurable damage to the earth. Trees can reduce storm runoff and capture it in underground water-holding aquifers, which, in turn, counter droughts. The water seeps through the trees’ natural filters over time, so the water supply is steadier and the rivers do not carry away the rainwater. Tree roots bind the soil to the earth and decrease the speed and intensity of the runoff. Leaves break the force of the wind and rain beating down from above. Trees filter sewage and farm chemicals, animal waste, and roadside spills, making it easier and cheaper to treat water before it enters your tap.

Interested in Becoming a Master Gardener?
Application Deadline: Friday, August 15, 2025

Check out the new program for master gardener learning through WSU’s Washington Green School. You’ll join a community of gardeners dedicated to protecting Washington’s environment and learn skills to garden responsibly in our changing climate. Learn practical techniques, connect with experts, and discover how your actions contribute to a healthier future for all.

For more information, go to Washington Green School. 

Apply to the Skagit County WSU Extension Master Gardener Program.

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Reducing wind damage and saving energy.
Trees located on the windward side of a property reduce the drying effects on the soil and vegetation in the summer or during a drought. In winter, these windbreaks can reduce snow drifts and even lower heating bills in the depths of a cold, stormy spell.
Providing habitat for a diversity of life.
Trees are used for food, shelter, and reproduction sites for various species. Many animals also nest and rest in their branches, hunt and capture prey from their hidden perches, and provide them with shade and shelter from the weather. Once a tree matures, its fruits become a food source. And when they are dead and dying, these snags are used by birds and insects for nesting hollows and foraging stations. Decaying trees become softer as they age, as fungi, bacteria, and wood-boring insects eat and break down the wood. The softwood tissue offers an ideal place for many young trees to begin their initial growth and development. The deadwood from these nurse logs also serves as ground cover that reduces soil erosion and prevents larger animals like deer from over-browsing plant seedlings. 
Shade and noise control.
Tree shade acts like a natural air conditioner that can keep down energy costs as well as making us more comfortable. Trees are planted to muffle urban noise from freeways and airports, and are almost as effective as concrete walls for this purpose. And much more pleasant to look at!

These are but a few examples of the majesty of trees in our environment. If you think that humans could live without them, think again. Now go out and give your favorite tree a big hug!

Know & Grow: Dahlias

Free, no registration required
Tuesday, August 19, 2025
1 pm – 2:30 pm
Sakuma Auditorium at NWREC
16650 State Highway 536, Mount Vernon

Visit the Skagit County Master Gardener Booth at the Fair

Exhibits Building “D”
Thurs. – Sun., Aug. 7 – 10, 2025
– Mystery Boxes where kids of all ages can explore nature by touch 
– Plants for firewise gardening
– Learn about building healthy soils for healthy plants

REFERENCES AND RESOURCES:

Bradford, N. (2016) The Many Benefits of Trees. National Environmental Education Foundation  (NEEF)

6 Ways Trees Benefit All of Us. (2020) The Nature Conservancy.

How Trees Make a Difference. National Wildlife Federation.

9 Reasons to Plant a Tree. (2018) Arbor Day Foundation.

Nix, S. (Rev. 2021) Reasons Living Trees are Valuable, Treehugger.

ABOUT THE AUTHOR:

Kathy Wolfe has been a Skagit County WSU Extension Master Gardener since 2002. She is co-manager of the vegetable garden at the Discovery Garden on SR 536 west of Mount Vernon.

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Questions about home gardening or becoming a master gardener may be directed to Skagit County WSU Extension Office, 11768 Westar Lane, Suite A, Burlington, WA 98233; by phone: 360-428-4270; or via the website

Washington State University Extension helps people develop leadership skills and use research-based knowledge to improve economic status and quality of life. Cooperating agencies: Washington State University, US Department of Agriculture, and Skagit County. Extension programs and policies are available to all without discrimination. To request disability accommodations contact us at least ten days in advance.

To Plant or Not to Plant: Trees to Avoid Planting in Your Yard

These endangered trees are likely to decline or die from the impacts of non-native insects and pathogens.

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By: Alison Hitchcock, Skagit County WSU Extension Master Gardener

Master gardeners are often asked for recommendations of trees to plant. These requests come in two flavors: what is the best tree for the clients’ preferences and landscape conditions, or what trees are inappropriate and best avoided? Many reputable websites provide numbered lists of the “best backyard trees” or, conversely, a catalog of “trees that you should, never, ever plant.”

The compilations of “trees that you should never, ever plant” tend to concentrate on undesirable characteristics such as messy or foul-smelling fruits, brittle stems, or heavy pollen production. Few include warnings concerning those species likely to decline or die from the impacts of non-native insects and pathogens.

The purpose here is to highlight tree species especially vulnerable to current and looming threats and suggest they should be added to your own “avoid planting” list. Property owners are encouraged to take early action by identifying unhealthy trees on their property during National Tree Check Month. 

Most of the public has some awareness of invasive pests; gypsy moth, chestnut blight, and Dutch elm disease are well-known examples. Data from our plant clinics shows that many other pests, more recent or less widespread, are well established in our area and have the potential for severe impacts of which the local community is generally unaware. The local community is generally unaware of many of these.

Trees Vulnerable	Agent	Comment
True firs: Noble, Fraser, Pacific silver	Balsam woolly adelgid (Adelges piceae)	Most commonly seen in MG plant clinics on Noble and Pacific silver trees. Grand fir was heavily affected in Oregon but not as severely here.
Native white pines (5 needles)	White pine blister rust (Cronartium ribicola)	2 and 3 needle pines were not affected. Non-native 5-needle pines have much lower rates of infection than native pines.
Birch (selected species)	Bronze birch borer (Agrilus anxious)	Native pests affecting non-native birches
Ash	Emerald ash borer (Agrilus planipennis)	Not yet a problem, but it is coming soon
Beech	Beech bark scale (Cryptococcus fagisuga) Beech leaf disease (unknown cause)	Not yet a problem, but it is likely to be soon

 

Noble fir with balsam woolly adelgid near Burlington Library © Photographer: Alison Hitchcock

Healthy noble fir © Photographer: Jeff Bisbee, USFS

Balsam Woolly Adelgid
The balsam woolly adelgid (BWA) (Adelges pinceae) is a widely established non-native insect that has become a pest of significant importance to all true firs around the county. The adelgid originated in Europe and first appeared in the Northwest during the 1920s. BWA shows up at the clinic every year, primarily on noble fir trees.

Adelgids are small, aphid-like insects that are always associated with conifers. A white and dense woolly wax covers adult adelgids. As it sucks sap from branches and boles (main stem below the branches) of a host tree, the balsam woolly adelgid injects a salivary substance that induces changes to the sapwood. The tree responds with knoblike, “gouty” swellings, which reduces the tree’s ability to translocate food and water.

Trees with crown infestations of BWA may take many years to die, while those with severe stem infestations die within five years, which is particularly important to Christmas tree growers. Control is difficult without a strict regimen of insecticide applications. Noble fir trees with chronic infections are scattered throughout Skagit County. (This author has yet to see a mature tree free of the disease). Look for tall trees with thinning crowns, dead branches, and an unaesthetic appearance.

White Pine Blister Rust
White pine blister rust is a fungal pathogen introduced from Asia. The fungus only attacks pines with clusters of 5 needles (white pines and not those with 2 or 3 needles.) This disease has virtually eliminated western white pine in western forests, causing a severe decline in native whitebark and bristlecone pines, both important ecological species. While all North American white pines are highly susceptible, non-native 5-needle pines have much lower infection rates.

The disease entered the US through infected nursery stock from Europe during the 1900s. Because tree nurseries in the United States were not yet well established, seedlings were grown (using native eastern white pine seed) in Europe and shipped to this country to meet reforestation needs. Because the first signs of infection are very subtle, the rust-infected seedlings were unknowingly imported.

White pine blister rust affects trees of all ages and sizes but spreads more quickly in areas with extended, cool, moist conditions during late summer and early fall. Pines are infected through needle stomata on wet needles. Following infection, the fungus grows down the needle and into the bark, where a perennial canker forms, eventually girdling and killing the branch. Branch infections are not too serious unless very abundant; stem infections are generally fatal.

White pine blister rust on the trunk. © Photographer: J. Schwandt, USFS, Bugwood

Infected western white pine removed from Salal Native Plant Garden. © Photographer: Alison Hitchcock

Most infections occur near the ground, where needles remain wet from dew and poor air circulation. Infections are apt to be lethal in young trees because branches are near ground level, and cankers develop closer to the main stem. Early pruning of diseased branches can be effective in reducing infection movement into the main stem and also help to increase air exchange. Prune juvenile trees as early as possible without removing excessive crown area, and gradually remove lower branches as the trees mature.

Those familiar with the Salal Native Plant Garden located south of the Discovery Garden (on Memorial Highway) may remember a western white pine that once existed immediately behind the Discovery Garden greenhouse. Despite heroic pruning efforts to keep the infection from spreading, the tree slowly succumbed to the disease and died. A small shrub in the Discovery Garden’s Fall and Winter garden room recently suffered a similar fate once the disease entered the main bole.

The current strategy for reintroducing western white pine to state and national forests is to increase the frequency of rust-resistant individuals across the landscape. The USDA Forest Service’s Pacific Northwest Region has had a screening and breeding program to develop resistance to the disease since the late 1950’s. Each year, resistant stock is grown at government nurseries to be out-planted in Oregon and Washington forests; unfortunately, infection rates continue to be high.

Bronze birch borer. © Photographer: Steve Katovich, Bugwood

Dead branches of infected birch trees in the Fred Meyer (Burlington) parking lot have been cut off. Dead trees have been removed. © Alison Hitchcock

Bronze Birch Borer
The bronze birch borer is a native insect that is a serious pest of ornamental birch trees, especially some white-barked species. While all species of birch can be attacked, non-native species are the most susceptible to injury. Borers primarily attack weakened, older, or drought-stressed trees. Problems regarding declining and dying birches have become an increasingly common issue seen at plant clinics during the last five years due to recurring droughts.

An early warning sign of borer damage is yellowing and thinning of foliage in the upper tree crown. The foliage will turn brown and drop from the branches by late summer. Infestations usually begin in ¾” to 1″ diameter branches, with symptoms progressing down the tree to the main trunk over successive years. Borers mine flat, irregular, winding galleries just beneath the bark, feeding in the phloem and severely injuring the vascular system. Attacked trees that survive will form callous tissue in the mines, which will become raised areas visible through the bark. Adult emergence holes are ‘D’ shaped and commonly accompanied by mottled, brown staining on the bole.

Borers do not survive in healthy trees, so keeping trees vigorous and adequately watered and planting resistant varieties is advised. A good look at the effects of borer damage can be seen on the non-native birches planted throughout the Fred Meyer parking lot in Burlington.

Emerald Ash Borer
The emerald ash borer (EAB) is a bright, green, buprestid beetle that lays eggs in the bark of ash trees. The larvae bore into the tree and feed on phloem tissue, effectively gridling the tree and resulting in tree mortality in as little as two years.

 Research has shown that EAB infested ash trees in Michigan 10 to 12 years before its initial discovery in 2002. The EAB probably entered the United States on solid wood packing material carried in cargo ships or planes originating in its native Asia. Since its arrival, the EAB has spread rapidly across North America and wiped out ash tree populations in the northeast. Green, white, black, blue, and pumpkin ash are on the listed “critically endangered” list. The insect has been found in 35 states and at least 5 Canadian provinces; it was discovered in Forest Grove, Oregon, in June 2023. Read more about the emerald ash borer in the WSU Publication Emerald Ash Borer and Its Implications for Washington State:https://pubs.extension.wsu.edu/Product/ProductDetails?productId=4755

Emerald ash borer © Photographer: Eric Day, VA Polytech Institute, Bugwood

Emerald ash borer infestation map © USDA Aphis

Research trials have shown that Oregon ash (Fraxinus latifolia), our lone native ash, is highly susceptible to EAB. Ashes have not been widely planted in our residential landscapes but are common in nearby shopping centers and other public areas. Ashes can be found in Burlington’s Best Buy, Costco, and Cascade Mall parking lots.

Beech tree with spreading canker and white patches of beech scale insects.
© Photographer: J. O’Brien USFS Bugwood

Fruiting bodies of neonectria fungus on beech © Photographer: Ansel Oommen, Bugwood
Beech Bark and Beech Leaf Diseases
Beech bark disease (BBD) is a disease of American beech, resulting from the infestation and feeding by the beech bark scale followed by infection with several native fungal species. The fungi cause bark lesions that grow and eventually girdle the tree. Beech scale was introduced into Nova Scotia from Europe in the 1890s and has been slowly progressing through the range of American beech as far south as Tennessee and west to Wisconsin. Over 50% of infected beech trees die within ten years of infestation.

Beech leaf disease (BLD) has been discovered recently, and much about it, including the full cause and how it spreads, is still unknown. It appears to be associated with a nematode, Litylenchus crenatae mccannii. First spotted in the northeast, the disease causes parts of leaves to turn leathery and branches to wither. The blight can kill a mature tree within six to ten years. It has now been documented in Canada and eight other US states.

Beech leaf disease.
© Photographer: J. O’Brien USFS Bugwood

Lesions from beech bark disease. © Photographer: L. Haugen USFS Bugwood

Timely Detection Increases the Chance of Successful Pest Management Efforts

We have yet to see either disease in Skagit County WSU Extension Master Gardener Plant Clinics since beech trees are not native to the Northwest, nor are they widely planted in our area. As a precaution, we do not recommend planting beech.

Every August, the Washington Invasive Species Council asks residents to check the trees on their property for signs of harmful insects or unhealthy trees as part of the National Tree Check Month. As summer progresses, many of the visible impacts from invasive species are most visible. Residents who suspect they have spotted an invasive species or tree disease should submit a report with detailed photographs to the Invasive Species Council’s mobile app or web portal https://invasivespecies.wa.gov/report-a-sighting/.

Pest infestations can be managed or even eradicated if caught early enough. Timely detection increases the chances of success and minimizes the cost of pest management efforts. A few minutes of inspecting your trees this August will help spot invasive insects, plant pathogens, and other types of damage before they have a chance to take hold.

ABOUT THE AUTHOR:
Alison Hitchcock has been a Skagit County WSU Extension Master Gardener since 2001. Prior to retirement, Alison worked for the Department of Natural Resources as the Northwest Regional Silviculturist.

Join us this coming Tuesday for a free Know and Grow Lecture-

Know & Grow Lecture Series
Season Extenders
Presented by Hallie Kintner
Tuesday, August 20, 2024 ~ 1 p.m.
Free Admission
NWREC Sakuma Auditorium
16650 State Route 536, Mount Vernon

 

 

REFERENCES AND RESOURCES:
Burns, K.S., Schoettle, A.W., Jacobi, W.R., Mahalovich, M.F. (2008) Options for the management of white pine blister rust in the Rocky Mountain Region. General Technical Report RMRS-GTR-206. Fort Collins, CO: US Department of Agriculture, Forest Service, Rocky Mountain Research Station. 26 p.

Cale, J.A., Garrison-Johnston, M.T., Teale, S.A. and Castello, J.D. (2017) Beech bark disease in North America: Over a century of research revisited. Forest Ecology Management: Elsevier Science: Amsterdam, Netherlands pp 394:86-103.

Davis, C. and Meyer, T. (2004) Field Guide to Tree Diseases of Ontario. Northern Ontario Development Agreement’s Northern Forestry Program Report TR-46: Sault St. Marie, Ontario, Canada.

Flower, C.E., Knight, K.S., and Gonzalez-Meler, M.A. (2013) Impacts of the emerald ash borer (Agrilus planipennis Fairmaire) induced ash (Fraxinus spp.) mortality on forest carbon cycling and successional dynamics in the eastern United States. Biological Invasions. 15(4): 931-944.

Lovett, G., et al. (2016) Nonnative forest insects and pathogens in the United States: Impacts and policy options Ecological Applications: Washington D.C. vol. 26 (5), pp 1437-1455.

Goheen, E.M., Willhite, E.A. (2006) Field Guide to the Common Diseases and Insect Pests of Oregon and Washington Conifers.USDA Forest Service, Pacific Northwest Region. R6-NR-FID-PR-01-06. Portland, OR.

Johnson, W.T., Lyon, H.H. (1988) Insects that Feed on Trees and Shrubs. Cornell University Press: Ithaca, New York.

Scharpf, R.F. (1993) Diseases of Pacific Coast Conifers. USDA Agriculture Handbook 521: Albany, CA.

Shaw, D.C., Oester, P.T., Filip, G.M. (2009) Managing Insects and Diseases of Oregon Conifers. Oregon State University Extension Service EM 8980: Corvallis, OR.

Sinclair, W.A., Lyon, H.H., Johnson, W.T. (1987) Diseases of Trees and Shrubs. Cornell University Press: Ithaca, New York.

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A Second Act for Your Square 1-Gallon Pots at the Discovery Garden!

Bring your leftover square 1-gallon pots to the Discovery Garden (16650 State Route 536, Mount Vernon). The bin for recycling the square 1-gal pots is located in the parking lot, just north (to the right) of the main entrance.
We only need square 1-gallon pots like the ones pictured below (bottom right). The recycling bin will be available now through fall. Simply put your pots into the bin, and we take care of the rest!

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Update on Western Redcedar Dieback in Skagit Valley Cities

Participate as a citizen scientist documenting the beloved western redcedars in your neighborhood.

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By: Sonja Nelson, Skagit County WSU Extension Master Gardener

The western redcedar (Thuja plicata) grew at Anacortes, Mount Vernon, and Burlington sites long before city founders officially set the current boundaries in 1879, 1889, and 1902, respectively. This tree species lived amiably with humans at their feet for many years. The trees grew old and tall, thrusting their tips above the human activity below, providing many basic needs for the indigenous communities and later the early European settlers. Like our ancient forebears, modern forest dwellers treasure these trees even though their numbers have dwindled as our cities have grown, and their benefit to humans today is mainly aesthetic. Without the redcedars, our verdant town landscapes of today would suffer significantly from the absence of these green giants in our midst-an almost unthinkable possibility until recently when droughts and heat have taken their toll on Washington’s forests.

Mount Vernon recently celebrated the 100th Anniversary of Hillcrest Park where many of the western redcedars are estimated to also be that old. Photo © Skagit County WSU Extension Master Gardeners

In 2022, the first peer-reviewed research made a definite link between the dieback of western redcedar in the Pacific Northwest and a warmer, drier climate.This research predicts that an upward trend in temperatures will occur. If these higher temperatures do occur, they could well affect the health of our western redcedars in Burlington, Mount Vernon, and Anacortes. as well as other communities in Skagit County. For this post, the author has focused attention on Mount Vernon, Burlington, and Anacortes. See the reference section below for links to data and information about other communities in Skagit County.

Mount Vernon, Burlington, and Anacortes are in the Puget Trough ecoregion, which runs the length of Washington state between the Cascade Mountains in the east, and the Olympic Mountains in the west. 

The native coniferous forest of western redcedar, Douglas fir (Pseudotsuga menziesii), and the western hemlock (Tsuga heterophylla) historically have dominated the Puget Trough ecoregion, thriving in a temperate climate of mild, wet winters and warm, dry summers. So far, the three dominant conifers have managed to survive urban sprawl. However, the signs of redcedar dieback manifestation in the Puget Trough have foresters, including forest experts in the cities of Mount Vernon, Burlington, and Anacortes, monitoring the western redcedars for dieback in their jurisdictions. Trees suffering from dieback can exhibit one or all unhealthy characteristics: a thin crown, topkill, a yellowing crown, and branch dieback. Topkill is one symptom of dieback, where the tree’s top branches die in response to drought or other stressors, such as excessive heat, leaving behind lifeless branches along the top of the tree that are often visible against the horizon. Other factors contributing to dieback include fungi and insects. Dieback of older needles is often normal and not a symptom.

Female cones ripen from September through October with 1-3 seeds per cone. Photo © Sonja Nelson
Western Redcedars Populated the Area Prior to Early Settlement
The towns of Mount Vernon and Burlington, rose from a forest floor where old-growth western redcedar, along with spruce, fir, and other timber, grew with little disturbance. Then, in the late 1880s, logging camps were established on either side of the Skagit River, with official boundaries set at the turn of the 20^th century. No old-growth western redcedars remain within the cities’ limits. Still, the remnants of second-growth redcedars are scattered about the towns on city-owned and privately-owned properties, adorning the towns in year-round green and reminding residents of the towns’ early homes in the forest.

Western redcedars on N. 30th Street in Mount Vernon are showing signs of dieback. Photo © Sonja Nelson

Dieback has occurred among several redcedars at the southern edge of Bakerview Park, most likely due to the compact turf beneath them. Photo © Sonja Nelson
Evidence of Western Redcedar Dieback
To estimate the presence of dieback in western redcedars in Burlington, Mount Vernon, and Anacortes this author visited the cities’ parks and used them as samples for the extent of dieback in the two towns.

In Burlington, many of the trees were cut for the development of playgrounds. However, a notable stand of redcedars grows in Maiben Park, also home to the Burlington Community & Senior Center. This grove is a splendid example of second-growth redcedars. Burlington Parks Supervisor Jim Rabenstein observed that dieback is not currently a problem in the park’s redcedars. However, in 2019, several Burlington residents reported concern about dieback in town. In response, the parks department hired certified arborists from Urban Forestry Services/Bartlett to assess the redcedars in Maiben Park. Approximately 100 native forest trees were assessed-about 94 were redcedars. The report noted the “exceptional nature of this grove,” with redcedars measuring up to 90 inches in diameter at 4.5 feet and in good condition. However, the report stated that drought mitigation planning will be essential in preserving this valuable community resource as long as possible. The report suggested that mulch be added under the trees to mitigate increasing drought stress and heavy foot and bicycle traffic under the trees.

In Mount Vernon, no significant dieback was evident in most of the city’s parks. Dieback, however, has occurred among several redcedars at the southern edge of Bakerview Park, most likely due to the compacted turf beneath them. Hillcrest Park, with its numerous redcedars in a natural setting, has yet to show any significant dieback. These second-growth trees are estimated to be at least as old as the park itself where, in March of 2024, the city held a 100^th birthday in celebration of the park’s founding.

Five years ago, a dieback of the western redcedars occurred at Little Mountain Park, a 522-acre park in southeast Mount Vernon. In response, Sean Corcoran, the Operations Supervisor in the Mount Vernon Parks & Enrichment Services, said that the city requested help from Washington State University Extension, Forestry Division, to assess redcedar dieback in a northeast section of the park. Forest experts determined that root rot (Armillaria) brought on by drought had caused the dieback. Crews removed most of the damaged trees.

Community Scientists and Western Redcedar Dieback Map
Washington State University, WSU, has invested considerable energy and resources in observing Western Redcedar dieback in Washington state via their WSU Extension Forestry division. Working from the hypothesis that redcedar dieback is a consequence of the region’s recent drought, WSU has launched the “Forest Health Watch” to keep track of dieback occurrences. To participate as a “citizen scientist,” access their website at https://foresthealth.org/redcedar and report the dieback. Your information will help confront the looming disappearance of these giants in our midst. A detailed map of “citizen scientist” reports is also available. The website also provides multiple links to research on identification, biology, ecology, distribution, ethnobotany, and relevant pests and diseases.

The best action today’s gardeners and homeowners can take to prevent redcedar dieback is to keep the soil around their trees weed-free and mulched and to discourage heavy foot traffic. Learn more about how to help your trees beat the summer heat.

REFERENCES AND RESOURCES:

Corcoran, S. Operations Supervisor, Mount Vernon Parks & Enrichment Services. Personal communication 6-11-23.

Forest Health Watch. https://foresthealth.org/redcedar

Gilles, N. New study sounds alarm, provides hope for western redcedar. Oregon Capital Chronicle. March 24, 2023. https://oregoncapitalchronicle.com/2023/03/24/new-study-sounds-alarm-provides-hope-for-western-red-cedars/

WSU Extension, 2018. Forester Notes-Western Redcedar, Washington State University, North Puget Sound Extension Forestry Newsletter, Volume 11, Number 2, July 2018

Puget Trough Ecoregion, 2023. Retrieved from: http://www.landscope.org/washington/natural_geography/ecoregions/puget_trough

Rabenstein, J. Supervisor, Burlington Parks Personal communication 6-11-23.

Reed, W. High and Dry for a NW Icon. Washington State Magazine, Fall 2023. Retrieved from: https://magazine.wsu.edu/2023/07/31/high-and-dry-for-a-nw-icon/

ABOUT THE AUTHOR:

Sonja Nelson is a Skagit County WSU Extension Master Gardener, Class of 2009.

Questions about home gardening or becoming a master gardener may be directed to:  Skagit County WSU Extension Office, 11768 Westar Lane, Suite A, Burlington, WA 98233; by phone: 360-428-4270; or via the website: www.skagit.wsu.edu/mg

Mark your calendar for these upcoming master gardener events:

Skagit County Fair
Thursday ~ Sunday, August 8-11, 2024
Skagit County Fairgrounds
Building D
(map)
Visit our booth, see our displays, and talk with master gardeners about how to make your garden beautiful and productive.
Know & Grow Lecture Series
Season Extenders
Presented by Hallie Kintner
Tuesday, August 20, 2024 ~ 1 p.m.
Free Admission
NWREC Sakuma Auditorium
16650 State Route 536, Mount Vernon

 

 

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A Second Act for Your Square 1-Gallon Pots at the Discovery Garden!

Bring your leftover square 1-gallon pots to the Discovery Garden (16650 State Route 536, Mount Vernon). The bin for recycling the square 1-gal pots is located in the parking lot, just north (to the right) of the main entrance.
We only need square 1-gallon pots like the ones pictured below (bottom right). The recycling bin will be available now through fall. Simply put your pots into the bin, and we take care of the rest!

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