Pest Alert: Top Kill in Western Larch

By Melissa Fischer, Forest Entomologist for Eastern Washington, Washington State Department of Natural Resources, melissa.fischer@dnr.wa.gov

Between June 2018 and November 2019, forest health specialists in North Idaho received 12 reports of top kill and mortality in western larch that appears to have been caused by a species of moth. Larvae collected from infested western larch were identified using DNA analysis. The closest match was a moth in the family Tortricidae, Cydia rana; a species native to the eastern U.S. The presumption is that the species found in Idaho is Cydia laricana. Cydia laricana is a closely related western species that was described infesting western larch near Missoula, Montana, more than 100 years ago. Unfortunately, no specimens are available for DNA comparison.

Although native, very little is known about the biology of C. laricana. This species has not previously been documented as a mortality agent and is therefore not well-studied. It appears that C. laricana tunnels into the wood to feed, develop, and possibly pupate. Following pupation, adult moths emerge, mate, and lay eggs. Similar moth species usually have a one- or two-year life cycle per generation. In Montana, adult specimens have been collected in May, suggesting that emergence and subsequent attacks on new trees may occur in spring.

While C. laricana has only been found infesting western larch in Idaho, it has been documented in both western larch and Douglas-fir in Montana. Infested western larch in Idaho have been found in both pure and mixed-species stands, sometimes scattered throughout the stand and sometimes found in small patches. Infested trees are between 3-14 inches in diameter and no more than 30 years of age.

The first symptom of attack is yellowing from the top down. The top kill progresses down the stem, sometimes killing the tree. Signs of attack include small canker-like areas (flattened, sunken, loose, cracking bark and viscous sap) on the main trunk and branches, and the presence of frass (excrement from the moth larva).

Management

Insecticides cannot be recommended due to lack of information on the C. laricana lifecycle, which is necessary in order to identify an appropriate application timing. Sanitation by removing and destroying (chipping or burning) infested trees may help reduce populations. Thinning may not be effective at increasing stand resistance, as a number of reports originated from young stands that had recently been thinned.

If you suspect Cydia laricana may be infesting your western larch in Washington State please contact Melissa Fischer, DNR’s Northeast Region Forest Entomologist, at melissa.fischer@dnr.wa.gov

For additional information and pictures, please see the Idaho Department of Lands’ complete factsheet: https://www.idl.idaho.gov/wp-content/uploads/sites/116/2020/02/Cydia-Fact-Sheet_12.6.19_2.pdf

Western Redcedar East of the Cascades: A Species in Decline?

By Melissa J. Fischer, Forest Health Specialist for Eastern Washington, Washington State Department of Natural Resources, melissa.fischer@dnr.wa.gov

Figure 1: Distribution of western redcedar.

Western redcedar (Cupressaceae Thuja plicata) is a beautiful, ecologically important and very valuable tree species found in eastern and western Washington. The full range of this species extends along the coast from northern California up to the southeastern Alaska. On the interior, its range extends from southcentral British Columbia down to western Montana and north Idaho (Figure 1). Western redcedar prefers moist growing sites with mild temperatures, but can be found on more harsh sites, particularly in the interior portion of its range.

What we’ve been seeing

For the past several years, forest managers, specialists and private landowners have noticed a change in their Western redcedar stands. Many trees have been exhibiting thinning crowns (Figure 2), heavy cone crops, discoloration (yellow or brown foliage; Figure 2), dead tops (Figure 3), and, sometimes, mortality (Figure 4). In comparison with the lush, green foliage typical of Western redcedar (Figure 5), these stands of dead and dying cedar have many people alarmed.

Figure 2. Western redcedar with thin crowns and brown coloration of the residual foliage. (All photos taken in Eastern Washington by Melissa Fischer, DNR)
Figure 3. Western redcedar with dead tops. (Melissa Fischer)
Figure 4. Recent mortality of Western redcedar. (Melissa Fischer)
Figure 5. Lush, green foliage of healthy Western redcedar. (Melissa Fischer)

How extensive is the problem?

The problem is not specific to eastern Washington.

It is in fact quite widespread, with reports coming in from all over Washington, Oregon, Idaho, and Canada. Unfortunately, the full extent of the problem is unknown. The most effective tool we currently have for capturing large-scale tree mortality is the Annual Forest Health Aerial Detection Survey. The Aerial Detection Survey is used to detect newly dead or defoliated trees within the forested acres of Washington state. Although some of the Western redcedar damage has been mapped, much has not.

Damage caused by bark beetles and defoliators tends to be much easier to see from the air, as this acute damage results in bright red crowns or large, contiguous stands of defoliated trees. Damage to Western redcedar appears to be a much slower process: Trees slowly lose needles, change color, and die back – a signature which is much harder to see from the air.

What is causing Western redcedar decline?

As of this time, it is unknown what exactly is causing the problem. There are many pathogens associated with Western redcedar, including various heart-rotting fungi and root diseases, but none of these issues has been found to be a common denominator. Few insects attack Western redcedar, and those that do usually attack when the tree is already dead or dying. Given the extent of the issue and the lack of a common biotic presence, the problem is likely abiotic.

Drought?

A very likely abiotic candidate is drought. A study by Seebacher (2007) found in a dendrochronological analysis (using tree rings and climate data) that Western redcedar dieback in British Columbia, Canada, was restricted to three hotter and drier sites out of four studied.

Figure 6: Average annual precipitation (left: inches, right: millimeters) in Washington state from 1895-2018 (green line). The gray line shows the overall mean and the blue line, the trend over time, an increase of 0.19 inches per decade. (Data Source: climate.washington.edu)

It is predicted that drought may become more prevalent in Washington state as the climate changes. Washington has had several recent droughty summers, but this may not be the singular issue given the fact that many of the Western redcedar stands exhibiting decline are located in rather wet areas. Looking at the climate data, the overall average precipitation in WA State from 1895-2018 actually shows a slight increase (+0.19ʺ/ decade; Figure 6).

If Washington is receiving more precipitation, how could drought be the problem? While the precipitation data does indeed show a slight increase in mean precipitation over time in the state, there are other factors to take into consideration, such as: Where in Washington state are these increases occurring? Is it throughout the entire state? What time of year is the precipitation occurring (winter, fall, spring, summer)? How is it falling (rain, snow, ice)? Perhaps the issue is the timing of precipitation. It’s possible that, regardless of the overall increase in mean precipitation overtime, that droughty conditions occurring during the hottest, driest parts of the year are what is negatively affecting Western redcedar.

Figure 7: Figure 6. Average annual temperature (left axis: °F, right axis: °C) in Washington State from 1895-2018 (purple line). The blue line shows the trend overtime; an increase of 0.2 °F per decade. (Data Source: climate.washington.edu)

What about temperature? A study by Gashwiler et al. (1971) found that of the mortality that occurred during their study of Western redcedar seedlings, 80 percent was caused by weather factors, with temperature being more critical than drought. Looking at the average temperature data from 1895 to 2018 in Washington state, there is a clear increase over time (+0.2°F/Decade; Figure 7).

It’s possible that Western redcedar are being affected by a combination of summer drought and higher temperatures. The summer months, part the growing season, trees are actively photosynthesizing, a process by which trees use sunlight, carbon dioxide, and water to produce glucose, i.e. their food. In order to obtain carbon dioxide, trees must open their stomata (microscopic cells on the underside of the foliage). When stomata are open, water is passively lost through transpiration. When it’s hot and dry, many species close their stomata to keep from losing too much water (isohydric adaptation). If a drought lasts for a long period of time, some trees may eventually begin to starve because they cannot photosynthesize and produce food with their stomata closed.

Other tree species leave their stomata open during drought conditions to continue photosynthesizing (anisohydric strategy). If the drought is prolonged, cavitation may occur. Cavitation is the breakage of water columns located in the trunk that move water from the roots to the foliage. If water is no longer reaching a twig or branch, that twig or branch will die. Species in the Cupressaceae family have an anisohydric adaptation to drought and thus are more likely to die due to cavitation (think gnarly dead trunks on Junipers in the dry pinyon/juniper woodlands of the Southwest).

Figure 8. Trends in April snowpack (measured in terms of snow water equivalent) in the western United States, 1955-2016. Blue circles represent increased snowpack; red circles represent a decrease. (Data source: Mote and Sharp, 2016 via Epa.gov)

Lack of snowpack?

Another abiotic factor to consider is snowpack. Figure 8 shows trends in April snowpack (measured as snow water equivalent or the amount of water contained within snowpack) from 1955-2016. April snowpack is particularly important because this will provide a slow supply of water throughout the spring, maybe even into the summer, as snow melts from the mountains down into the lowlands. As can be seen, snowpack has declined at more than 90 percent of the sites measured. The average change across all sites is a loss of about 23 percent. Large and consistent decreases have been observed throughout the western U.S., but have been especially prominent in Washington, Oregon, and the northern Rockies.

Let’s Delve a Little Deeper:

An interesting hypothesis: Yellow cedar decline (D’Amore et al. 2009)

As much as we would like things to be simple (i.e. there’s one specific disease or insect affecting our Western redcedar and it’s a manageable problem), in the world of ecology, problems and solutions tend to be much more convoluted. Let’s take a look at the case of another Cupressaceae species, Alaska yellow cedar (Cupressus nootkatensis). This species is believed to have been on the decline for 75-plus years in southeast Alaska and British Columbia. Drought and lack of snowpack have been related to the decline, but an interesting hypothesis for this decline shows that the specific causes can be much more complex …

A distinctive trait of the Cupressaceae family, under which both yellow cedar and Western redcedar fall, is that they accumulate calcium in their tissues. Why calcium? As most everyone knows, trees, plants in general, need nitrogen. Many conifers uptake ammonium (NH4+), but cedars preferentially uptake nitrate (NO3-) as a competitive adaptation on marginal sites. A byproduct of nitrate assimilation is oxalic acid, which is a potentially toxic compound. Calcium neutralizes oxalic acid to form calcium oxalate; in other words, cedars are using the calcium they are accumulating as a detoxification process.

Cedars have two features that help with uptake of both nitrate and calcium: early dehardening (plant tissues lose hardiness and are ready to resume growth early in the season) and shallow rooting. Early dehardening of yellow cedar allows fine roots near the soil surface to access soil rich in ammonium and calcium in early spring. This strategy only works if roots are protected from freeze/thaw events that induce root injury. Historically, consistent snowpacks have limited soil freezing and protected roots from extensive damage, but depths of snowpack, particularly at lower elevations in northern latitudes, have declined during the 20th century. The shallow depth and early spring activity of roots that historically enhanced the competitive status of yellow cedar on wet soils may now be the reason behind its decline.

Could this hypothesis for yellow cedar decline be applied to Western redcedar as well? It certainly is a possibility and would explain why we are seeing Western redcedar dieback in areas that appear to have plenty of water year-round.

What can be done?

Given the fact that we don’t know exactly what is causing Western redcedar dieback and mortality, there is currently no sound management advice available. We often suggest thinning stands to allow more availability of resources to the residual trees, but in the case of yellow cedar, open canopies were found to lead to greater exposure and associated temperature changes that in turn lead to increased soil-freezing events and root freezing injury. Clearly more research is necessary, but funding for research in the field of forest health is hard to come by and quite competitive when available.

Figure 9 shows the predicted future range of Western redcedar in green; red denotes the area where Western redcedar might be found, but under stressed conditions. Gray denotes a large portion of the current range, which is predicted to become the historic range. This is a bleak future for such an important species.

Figure 9. The predicted future range of western redcedar in and around Washington state. Green denotes a range expansion, dark gray the historic range, and red, areas where western redcedar may occur in the future, but where it will be stressed. (Data provided by: Nicholas C. Coops, Richard H. Waring, Amanda Mathys via Databasin.org)

For more information, please refer to the resources listed below.

D’Amore, D.V., P.E. Hennon, P.G. Schaberg, G.J. Hawley. 2009. Adaptation to exploit nitrate in surface soils predisposes yellow cedar to climate induced decline while enhancing the survival of western redcedar: A new hypothesis. Forest Ecology and Management. 258 (2261-2268).

Gashwiler, J.S. 1971. Emergence and mortality of Douglas-fir, western hemlock and western redcedar seedlings. Forest Science. 17: 230-237.

Mathys, A., Coops, N.C. and Waring, R.H. 2014. Soil water availability effects on the distribution of 20 tree species in western North America. Forest Ecology and Management 313: 144-152.

Mote, P.W., A.F. Hamlet, M.P. Clark, and D.P. Lettenmaier. 2005. Declining mountain snowpack in Western North America. Bull. Amer. Meteor. Soc. 86(1):39–49.

Mote, P.W., and D. Sharp. 2016 update to data originally published in: Mote, P.W., A.F. Hamlet, M.P. Clark, and D.P. Lettenmaier. 2005. Declining mountain snowpack in Western North America. B. Am. Meteorol. Soc. 86(1):39–49.

Mote, P.W., A.F. Hamlet, M.P. Clark, and D.P. Lettenmaier. 2005. Declining mountain snowpack in Western North America. B. Am. Meteorol. Soc. 86(1):39–49.

Seebacker, T.M. 2007. Western redcedar dieback: possible links to climate change and implications for forest management on Vancouver island, B.C. Thesis Master of Science. The University of British Columbia.

My Larches Look Sick. What Could it Be?

By Melissa Fischer, Eastern Washington Forest Health Specialist, Washington State Department of Natural Resources, melissa.fischer@dnr.wa.gov

I have noticed quite a bit of damage to western larch foliage this season.

Upon close inspection, I have found that much of it is due to the larch casebearer, an invasive species of moth introduced into the United States in 1886 from Europe. In the larval stage, the larch casebearer damages both our dominant Western larch (Larix occidentalis) and the more eastern and northerly tamarack (Larix laricina) by defoliation.

Lifecycle

The larch casebearer (Coleophora laricella) has one generation a year, with adult moths emerging from the end of May through early July. After mating, the females lay between 50 and 70 eggs singly on larch needles. After the eggs hatch, the larvae bore directly into larch needles.

The larvae will develop through four instars (developmental stages between molts) prior to pupating. They will mine a single needle for about two months, during which time they will develop from the first to second instar.

Once hollowed out, the larvae will make a case from the needle (hence the name “casebearer”) by lining a portion of it with silk and chewing it free from the rest of the needle. The larva will reside within this case through the third instar, feeding from mid-August to late October.

In the fall, larvae leave the foliage before needle shed and attach their cases to twigs, overwintering within the case as third instar larvae. In the spring, the third instar larvae will begin feeding again. They develop into the fourth instar, and then pupate inside their cases around late May.

The cycle begins again when the adults emerge from their pupal cases.

How do I know if its larch casebearer damage?

Casebearer damage to larch foliage can be seen in the early spring. The tops of mined needles will look straw-colored, curl over, and/or look wilted (Image 1). By early summer, the foliage will turn reddish-brown.

By mid-June to mid-September, much of the damage visible in the spring will be concealed by green foliage that appears when new shoots elongate and/or if a second crop of needles develops. Mining in late September may brown the trees again, but by then the tree has completed its growth, so damage is minor.

larch 1
Image 1 A. Larch casebearer damage to western larch contrasted with an undamaged tree in the foreground and B. Close-up of larch casebearer damage to foliage of western larch.

The casebearer itself can be seen in the early spring attached to needles within their cases. Later in the spring, pupal cases can be found attached to needles or hanging from the ends of silk off larch trees. This can be quite a spectacular display if the tree has been heavily infested. The cases are straw-colored and less than a quarter of an inch long (Image 2). Many landowners describe the cases as looking similar to grains of rice.

The adults can be found around June and are pretty nondescript, being less than ¼ of an inch long and silvery (Image 3). If you look closely with a hand lens, you may see that the ends of the wings are fringed (Image 4).

larch 2
Image 2. Larch casebearer cases attached to western larch needles. The needles in this picture are quite long for western larch, but these particular trees were open-grown and well-watered.

Cases may again be seen from the end of August through to the next season on needles or overwintering on twigs.

The larch casebearer is not the only cause of damage to larch needles. Larch needle blight (Hypodermella laricis, Image 5) and larch needle cast (Meria laricis), both fungi, can cause similar damage. Larch needle blight damages needles in the spring and needle cast affects needles in the summer. Close inspection of the needles themselves will help you determine whether the damage is caused by the casebearer or a fungal infection.

Should I worry?

larch 3
Image 3. Larch casebearer adult: side view

Larch casebearer damage can look quite serious, but one year of damage is typically not something you need to worry about. Larch trees are capable of putting out another flush of needles within the same season and, because they are deciduous, they will refoliate the following spring.

In addition, the larch casebearer is especially vulnerable to a suite of parasitoids, especially two European parasitic wasps, Agathis pumila, a braconid, and Chrysocharis laricinellae, a eulophid, that were introduced in the early 1960s as biological control agents. Both parasitoids are well established and very successful at reducing casebearer populations. Studies have shown that either wasp can parasitize over 90 percent of the larch casebearer population in an infested area. Samples I collected this spring in Eastern Washington had the same results.

larch 4
Image 4. Larch casebearer adult: Notice the fringe at the end of the wings.

If your larch experience continued heavy defoliation for five or more years, you may begin to see the trees decline. Evidence of decline will begin with branch dieback. After a few years, entire branches may begin dying, followed the next season by epicormic branching along the trunk. Within another one to two years, the tops of the affected trees may die.

Soon after these symptoms appear, tree mortality may occur. Trees weakened by continued defoliation are also susceptible to other insects and disease, such as western larch borer and Armillaria root rot.

There are no known silvicultural controls for larch casebearer. Insecticides over large landscapes are not economically practical, but may be advisable in high-valued stands or individual trees. Typically, natural controls are effective, particularly parasitoids.

In addition to parasitoids, prolonged cold and wet weather in the spring, with frosts after the larvae have emerged, can also cause considerable damage. Droughts that last into the late summer causing needles to dry out and fall off also reduce populations. Needle blight and needle cast also have the capacity to reduce the larvae’s food supply.

larch 5
Image 5. A. Larch needle blight damage to western larch and B. Close-up of larch needle blight damage.
larch 6
Image 6. Parasitoids of larch casebearer that emerged from samples taken in Eastern Washington, 2019 A. braconid and B. Eulophid.

For more info:

Pederson, L. 2006. Management Guide for Larch Casebearer. Forest Health Protection and State Forestry Organizations. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5187464.pdf

Tunnock, S. and R. B. Ryan. 1985. Larch Casebearer in Western Larch. Forest Insect & Disease Leaflet 96. U.S.D.A. Forest Service. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_043608.pdf

Forest Thinnings and Hydrology: A Request for Input to Research Project

Washington State University Forestry Extension Specialist Andy Perleberg and University of Idaho Extension forester Chris Schnepf have been working with forest researcher Ryan Niemeyer on a study about relationships between hydrology and forest thinning in Inland Northwest forests. The U.S. Department of Agriculture-funded project is a cooperative effort between many partners, including the Washington Farm Forestry Association, Colville Tribes, Yakama Nation, WSU, the University of California at Santa Barbara, the University of Idaho, and, potentially, you.

Niemeyer is seeking small forest landowners to participate in a survey related to this project. Below is a link to a very short online form where you can submit your basic contact information for the forest thinning survey.

Ultimately, this work will help inform land managers about the effects of thinning treatments on forests in the inland west, and help us deal with ongoing issues related to drought, bugs, disease, and fire.

To participate, go to forms.gle/p4hk9kWhiw19d4D46.

If you know other forest owners whom you think might be interested in participating in this, feel free to pass this information along.

For more information about the project, go to rniemeyer4.wixsite.com/nwforestthinning.

What About Banana Slugs?

 “We’d be up to our eyeballs in (organic) debris if those guys weren’t at work!”

Richard Zabel, Executive Director of the Western Forestry and Conservation Association

“Dr.” Zabel is remarkably insightful in his commentary on the role of decomposers; those amazing organisms that break down material in ecosystems. Forests need a lot of these, acting continuously, for our forests contain an enormous amount of organic material ultimately produced by photosynthesis. A normal west side forest in the Pacific Northwest contains somewhere between 330 and 790 tons/ acre of standing biomass**. That’s a lot. And all of this material must eventually decompose into foundational elements, feeding the nutrient cycles and ecology of our forests.

Wow. Just wow. Good thing this stuff breaks down.

Ever hear of “charismatic mega-fauna”? These are creatures that easily capture our attention; critters like grizzly bear, elk, mountain goats or cougars. These animals usually function at high levels in the food chain, eating plants or being eaten out on the Serengeti of our imaginations.

Now, back to decomposition. It is one of the most important ecological functions going, keeping our nutrient cycling going and feeding the plants and fungi of the world. The animal the esteemed Zabel was referring to is:

Ariolimax columbianus

Our own banana slug! Now that’s charismatic mega-fauna.

They are the second largest slug in the world, growing up to 12 inches long — but most are between 4 and 6 inches long. They come in a variety of colors, such as olive green, gray with black spots, yellow, even white. Local areas may have similar color patterns*, which could be adaptation in action. They occur in moist forests all along the Pacific coast of North America.

A handsome banana slug with tentacles extended. (Photo by Ken Bevis, DNR)
A handsome banana slug with tentacles extended. (Photo by Ken Bevis, DNR)

There are four funky stalks on their head. The upper ones are eye stalks for light reception, and the lower ones are chemical receptors used to “taste” the environment. Racing slugs at the University of California Santa Cruz (home of the Fighting Banana Slugs) open their breathing hole wide when competing****. It is on the right side of the animal, called the pneumostome, and allows the single lung to open and gather oxygen when the slug is working hard. (Yes, even slugs hurry sometimes.) Otherwise, in normal relaxed slug mode, they get enough oxygen through their wet, mucous-covered skin.

Speaking of slime, banana slugs have a magnificent tool in their mucous coating. They have glands all over their body that provide this slick and slimy multi-purpose coating. It protects them from dehydration, and allows them to cover themselves in a ball of the gooey stuff to hole up during dry spells. (That’s why you don’t see them out and about in the heat of summer.)

Ever wonder how slugs cruise along so gracefully? They don’t actually crawl across the forest floor at all. They lay down a trail of perfect slime to slide over, and that let’s them move with a certain undulating grace. It is at once slippery, and sticky, and allows them to climb vertical surfaces. And the slime is full of chemical signals telling other slugs which way they went, and whether they might be a potential mate. They even eat mucous to replenish their own supplies.

Banana slugs, despite their savory name and appearance, have very few predators thanks to this mucous. It apparently tastes bad and few animals have developed a taste for it. Raccoons will sometimes roll them in dirt to cover the slug (and the flavor?) and then have slug sushi, but mostly, they are left alone. Slug slime is a miracle, multi-purpose substance!

Banana slugs never have to worry about getting a date either: Not because they are so wonderfully handsome/beautiful (although they are in their own mollusk-y way), but because they are hermaphrodites. Yes, slugs are both boy and girl at the same time. They do look for a mate during the wet spring, and exchange sperm in an amazing mating ritual involving hanging by slime threads, exuding their enormous sex organs, and intertwining in, well, a rather sensuous manner (check out the you tube of Richard Attenborough watching their European cousins, the Leopard slugs). And afterwards, Romance? Commitment? Nope. Each slug goes off separately and lays eggs in moist, rotting wood, leaving their kids to their own fates. Slugs don’t do family or child care, so the hatched-out miniature slugs are on their own from day one. No divorces or day care bills for banana slugs!

Most significant to us, banana slugs eat detritus (rotting plant material) and mushrooms. They are important players in the forest ecosystem as nutrient and material recyclers, breaking complex plant matter down into basic components that can further move in the ecosystem. ***

So next time you see a groovy, big banana slug cruising along in your forest, treat it with a little respect and admiration. They are on duty for all of us, doing critical ecosystem functions with little fanfare and appreciation.

And when I searched on Slug Songs, there’s even a video of dancing slugs. Who’d a thunk it!

Sammy the Slug: Now that’s a mascot! (Bing images)
Sammy the Slug: Now that’s a mascot! (Bing images)

Send me photos and stories about the wonders of wildlife, and your own Encounters of the Slug kind, in your forests!

*Source: Slater Museum blog post, “The Pacific Northwest is Slug Country”, July 2016.

**Stewart T. Schultz (1990).  The Northwest Coast: A Natural History.  Portland, Oregon, Timber Press.

**Waring, RH, and JF Franklin. (1979).  Evergreen coniferous forests of the Pacific Northwest.  Science 204: 1380-1386.

**Waring, RH, (1982) Land of the giant conifers.  Natural History 91(10):54-63.

*** Wikipedia and various other sources for cool facts about slugs.

**** I’m not sure if they really do this but it seems like a good idea and probably has happened down there sometime!

Ken Bevis, DNR Stewardship Biologist, Ken.Bevis@dnr.wa.gov

Douglas-fir Damage May Be Caused by Secondary Bark Beetles

This spring and summer, the Washington State Department of Natural Resources (DNR) received numerous reports of dead or damaged Douglas-fir trees throughout the state. Symptoms include entirely red crowns in saplings and red tops or scattered red branches in trees. The damage is more common in dry lowland areas and sites with well-drained soils.

DNR forest health specialists examined Douglas-firs with these symptoms and found unexpected levels of attack by several species of bark beetles such as Douglas-fir engraver, (Scolytus unispinosus), Douglas-fir pole beetle (Pseudohylesinus nebulosus), and another engraver beetle, Scolytus monticolae, that has no common name.

Picture of a Douglas-fir engraver.
Douglas-fir engraver. (Photo by Joseph Benzel, USDA APHIS, bugwood.org)

These beetle species are normally considered ‘‘secondary’ because they typically infest trees that are first weakened by a larger, primary issue such as root disease, fire damage or drought stress. Secondary beetles can damage trees under stress but normally lack the capacity to kill live, healthy trees.

Douglas-firs have been particularly affected by Washington’s abnormally hot and dry summers over the past three years. Back-to-back drought years are stunting the health of Douglas-firs, leaving them less able to fend off insect attacks.

These conditions have allowed secondary bark beetle species to establish in healthy Douglas-firs and boost beetle populations, causing significant damage or even killing some trees. Secondary bark beetles mostly prefer to attack small-diameter trees, yet recent investigations have found them in stems of larger diameter trees as well, which is historically uncommon.

Consider the following to prevent or manage secondary beetle attacks in Douglas-fir:

  • Keep forested stands thinned so that remaining trees can access more of the water stored in soils
  • Irrigate and mulch high-value yard or park trees during prolonged periods of drought
  • Avoid fertilizing trees, as this can increase foliage growth and the need for more water
  • Do your homework before applying pesticides:
    • Some systemic pesticides can be applied as a preventative measure for high-value trees
    • Pesticides are not effective at controlling beetles in trees that have already been attacked
    • Consider hiring a licensed pesticide applicator to ensure the proper selection, timing and application of pesticides

Unfortunately, pheromone treatments, such as those used to deter the more aggressive Douglas-fir bark beetle (Dendroctonus pseudotsugae), are not available to combat these minor bark beetle species.

For more information on forest health in Washington, go to www.dnr.wa.gov/ForestHealth or contact DNR’s forest health staff at 360-902-1300.

Article by Glenn Kohler, DNR Forest Entomologist, glenn.kohler@dnr.wa.gov

Restoring Forest Health, One Neighbor at a Time

Forest health conditions in Washington state have been in decline for decades, contributing to catastrophic and uncharacteristically severe wildfires – and the state’s Department of Natural Resources is reaching out to partners, including small private forest landowners, to work toward a solution.

Insect pests, disease, invasive plants and animals, human development, climate change, past forest management practices, and a lack of adequate active management have, in combination, created a perfect storm for poor forest health and wildfire risk.

Healthy forests are vital to clean water and air, the economy, carbon sequestration, fish and wildlife habitat, and recreational opportunities. But without significant intervention, the problems our forests face will continue to compound. To restore health to our forests, DNR has developed a 20-year Strategic Forest Health Plan committed to treating 1.25 million acres of unhealthy forestland in Central and Eastern Washington by 2037.

forest health strategic plan coverThe plan is unprecedented in its scope and application. It embraces an all-lands, all-hands approach, recognizing that solutions for improving forest health must span property lines and government jurisdictions. Coordinating forest health treatment efforts with all willing forest landowners in high-priority watersheds is a key part of the forest health plan. DNR worked on the plan with more than 30 agencies, interest groups and organizations, representing private, state and federal forest landowners, state agencies, tribes, the forest industry, universities and conservation groups.

One of DNR’s key landowner groups is you, the small private forest landowner. Our agency has foresters on staff to provide you with forest health evaluations, technical assistance and cost-share programs to help offset the expense of forest health treatments.

We are eager to connect with you, so please call us at 509-925-8510 if you own forestland in Adams, Asotin, Benton, Chelan, Columbia, Douglas, Franklin, Garfield, Grant, Kittitas, Klickitat, Lincoln, Walla Walla, Whitman, and Yakima counties; or 509-684-7474 if your forestland is in Okanogan, Ferry, Stevens, Pend Oreille, and Spokane counties, or the northern portion of Lincoln County. When you call, ask to speak to someone from the Landowner Assistance Program.

For more information on the 20-year Forest Health Strategic Plan, visit www.dnr.wa.gov/ForestHealthPlan.

By Julie Sackett, Forest Health Division, julie.sackett@dnr.wa.gov