Tag Archives: forest health

Stressed and Dying Conifers: Another year for “Valley Crud”

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drought stressThe phone has been ringing off the hook lately with calls from people describing sick and dying Douglas-fir and other conifer trees. The trees are of a wide range of ages and in many environments and settings, although most calls have been coming from within the valley margin and have to do with young trees.

So far, the answer is generally: “It is drought stress”.  Huh, in May? Well it has been a dry winter and spring, … but that is not the issue.

My best explanation is that we had a pretty hard end of summer last year. Remember that? NO rain until mid-October then, Boom, it was winter. By then, many trees had started running out of water, killing tops or branches, and leaving leaders and branches susceptible to attack by various opportunistic pests.

We started seeing a few classic signs of drought stress (tops dying and branches “flaring out”) at the very end of the season last year, but late enough that many did not have time to show up before the weather turned. Injuries had occurred, so it was just a matter of time before they expressed themselves, which is happening now. The recent hot weather seems to have made it more sudden and dramatic.

This happens from time to time. Here are two good articles a few years back by the ODF Forest Health team explaining Dead tops and Branches (with Good pictures), and about Drought and Mortality.

It is important to keep in mind that the Willamette Valley can be a challenging climate for trees. Many of our soils in the valley are poorly drained, which is hard on most of our conifers, and other soils are fairly shallow and cannot hold much water. Also our summers are hotter and drier than in the mountains. Heat and drought stress can kill trees outright, or more often just put the trees under stress, which can then lead to pest problems (as explained in the two publications above). From what I am seeing and hearing, the major cause of the problem now seems to be drought stress. Insect or diseases which able to take advantage of a stressed tree’s condition may sometimes be involved, but they are generally not the cause of the problems.

Finally, weather can be more stressful when trees are overcrowded, so thinning stands to keep trees vigorous with adequate growing space may be helpful in the long term. Right now, we just have to wait it out, and hope we get some serious rain this year, or we will see this problem intensify.

We all better get out there and wash the car…..

Brad Withrow-Robinson

Bugs, the good and bad (dead wood revisited)

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In response to last week’s post on the value of dead wood in the forest, I received this e-mail from a landowner:

“We’ve never left much on the ground in the way of dead wood…not during logging, but wind damaged, etc.  Our thought has always been that these rotting logs increase the insects in the forest, both good and bad. Is this a valid concern and if so, where is the balance between bugs and wildlife?”

He raises a point worth exploring. While calling an insect “good” or “bad” is a matter of perspective, for the purposes of this discussion let’s assume that “bad” insects are those that cause economic or environmental damage, and “good” insects are those that don’t. The vast majority of insects that inhabit western Oregon forests fall into the “good” category…with a few notable exceptions.

One of these “bad” bugs that the e-mailer might have in mind is the Douglas-fir beetle. This time of year, the adult beetles are flying around in search of Douglas-fir trees where they lay their eggs underneath the bark. Their favorite targets are large diameter, freshly downed logs—or standing trees that are weakened from another cause (root disease, soil compaction, etc.). Through the summer and winter, the eggs hatch and the larvae grow as they tunnel around under the bark (this activity is what kills the tree). The following spring, they have become adult beetles, and they fly away in search of new homes. If they can’t find another weak tree or fresh log, they will go after a healthy tree.

Douglas-fir beetle (Dendroctonus pseudotsugae ) on Douglas-fir (Pseudotsuga menziesii ) - 1587008
reddish bark dust in bark crevices is a sign of the Douglas-fir beetle (Photo: Elizabeth Willhite, bugwood.org)

Healthy trees can withstand a low-level Douglas-fir beetle attack, and in normal circumstances there are rarely enough beetles around to cause concern. The problem arises when the beetle population builds up and lots of them infest a healthy tree at once. When does that happen? In situations where there is a lot of freshly downed or damaged wood on the ground for them to target initially – like after a winter windstorm.

Here’s a true story for illustration.

In fall 2009, a landowner in the Coast Range was hit hard by beetle kill to his otherwise healthy, 100+ year old forest. Why? Here’s how we think this may have played out.

  • The stand is adjacent to a sawmill.
  • The big windstorm of December 2007 created lots of blowdown along the coast, though this particular stand was too far inland to be damaged.
  • Some of the coastal blowdown was not salvaged until summer 2008…too late, because Douglas-fir beetles had already found them during the spring.
  • The salvaged logs were brought to the mill, along with the beetle larvae living under the bark.
  • Then, in late 2008 the recession hit and the mill curtailed operations. The logs sat in the deck…and the beetles matured.
  • In spring 2009, they emerged and flew off to the neighboring stand, where they attacked the healthy, mature trees.

It was a sad situation, especially since the landowner had to cut more trees to avert further beetle damage, and in a poor market.

So, back to the e-mailer’s question: does retaining snags and downed wood for wildlife create a forest health risk? The take-home messages are these:

  • Most insects are not forest health risks.
  • In western Oregon, the Douglas-fir beetle (the “baddest” dead wood-inhabiting insect) only thrives in FRESHLY dead or downed trees. Once the snag or downed wood has been dead for more than a year, it is no longer a target. Instead, it will become inhabited by the dozens of “good” bugs that feed wildlife.
  • There needs a LOT of this fresh down wood to pose a forest health risk – like after a storm. According to Oregon Department of Forestry, a good rule of thumb is that fewer than 3 FRESH down logs/acre does not present a hazard.

After a windstorm or other stand-damaging event, yes, prompt salvage is important in order to prevent a beetle infestation. But, when scattered trees gradually die in a stand from other causes, it is hard to imagine when this would create a risky situation with respect to bark beetles. And during harvest activities, you can be strategic about how much dead wood is left behind, and in what conditions.

We appreciate it when readers respond to our blog posts. We like your e-mails, but you can also respond by commenting directly on the blog, where other readers can contribute to the conversation.

Amy Grotta

“Is Swiss needle cast hurting me?”

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I recently got a call from a guy selling some woodland property in the Coast Range. A prospective buyer recently told him that he had Swiss needle cast (SNC) and so was not interested in buying the property. It is not hard to find the disease in western Oregon. It is a native disease of Douglas-fir and is wide spread from the coast into the Cascades. But this fellow was calling for some guidance about how to respond to this concern. Was it reasonable? How can he gauge its impact on his young forest stand?

Phot credit: SNC Coop

He already knows how to recognize SNC when he sees it: from a distance it makes a tree look paleand sparse. This is because the fungus is developing in the needles, gradually clogging the stomates, which is where the leaf exchanges water vapor, carbon dioxide and oxygen. Up close with a hand lens you can look on the underside of a diseased needle and see tiny black dots in neat rows where healthy white dots (the stomates) should be visible. In some places or during seasons when the disease is severe, this causes many needles to turn yellow, and eventually to drop (to cast), giving the recognizable symptoms. If enough stomates get plugged, and or enough needles are cast the disease begins to affect photosynthesis, and possibly growth, the crux of the caller’s question.

“The key to understanding the impacts from Swiss needle cast,” says Dave Shaw, OSU Extension Forest Health Specialist and Director of the SNC Cooperative, “is whether the needle retention on the tree is good or not. If the tree is retaining around 3 years of needles, then growth should be close to normal. The impacts occur when needle retention is below three years, and especially when it drops to 2 years or less.”

Photo Credit: SNC Coop

So, the question for the caller is: “What is your average needle retention in these stands?” If near 3 years, he can tell folks that yeah, the disease is around but the stand is doing ok.

To count needle retention, use binoculars and cruise the stand, taking the needle retention from the mid crown, south side of tree, and not the apical stem, but the 4-yr and older side branches. There is a good illustration of branching and needle cohorts on page 3 of Swiss needle cast of Douglas-fir in Oregon. This time of year is good. Even if the stand is discolored a little, needle retention is the key factor.

More information about SNC can be found on the SNC Cooperative website, which has aerial survey data, research findings and even a Stand Assessment Tool that provides a more quantitative approach to assessing impacts on growth.

Brad Withrow-Robinson

Flea beetles skeletonize red alder leaves

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Submitted by Glenn Ahrens, OSU Extension Forester, Clackamas, Marion & Hood River Counties

Alder flea beetles are particularly active this summer as they go about their business of skeletonizing leaves on red alder trees. I have seen this come and go over the years, and generally flea beetles are not a serious threat. Flea beetle flare-ups in the forest usually run their course after 2-3 years, after which their population crashes – similar to western tent caterpillar infestations. Healthy alder trees with good vigor are usually not seriously affected. Stressed alder trees – particularly those in dense thickets – may die after 2-3 consecutive years of flea beetle infestation. If you like your red alder trees and want to promote “good vigor” the best way is to 1) avoid growing alder on poor alder sites and 2) keep trees well-spaced to ensure large healthy crowns.

Return of the tent caterpillars

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The western tent caterpillar is a native insect to our forests. It population is cyclical. Over a period of two to three years, the population builds up and then crashes as natural parasites and diseases kill them off. Then we don’t see them again for maybe 8 – 10 years.

This week I saw some tent caterpillars in a recently planted site near Clatskanie (see photo). Last month, I saw lots more over by Sisters, where they were all over the bitterbrush around our family’s camping spot (“eew”, proclaimed my 9-year-old). Here on the westside, they prefer hardwoods such as alder, cottonwoods and willows.

While they may look alarming and can substantially defoliate the trees they infest, there’s little cause for alarm. The caterpillars are done feeding by late June, and the affected plants typically regrow a new set of leaves later in the summer. There’s no reason to spray insecticide – the best strategy is to wait it out and let nature take its course.

My guess is that we’ll see more western tent caterpillars in some localized areas next year.

What’s big, black and white, and not a pest?

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Summer must be coming to an end. I say that not because the kids are going back to school or the tomatoes are (finally) starting to turn red, but because today I got my first call of the year about a strange and striking looking insect.

This is a banded alder borer. It is a native wood boring insect, but it is not considered a forest pest because it generally infests dead or downed wood (people often find them on their firewood piles). This insect is often confused with the Asian Longhorn Beetle, which is one of the nation’s most un-wanted invasive pests. If you find a large, black and white insect with long antennae, chances are it’s the banded alder borer (the good guy), but to be sure, look for a white head with a large black dot on it. See the photo above.

I am not sure about the banded alder borer’s life history, but I think the adults must be most active in August and September because that’s when the calls and emails start to come in.

Green Alder Sawfly – A New Invasive

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By Paul Oester and Dave Shaw, OSU Extension Service

History
A native of Europe, North Africa and the Near East, the green alder sawfly (Monsoma pulveratum) (Hymenoptera: Tenthredinidae) was first found in North America in eastern Canada in the early 1990’s, then in Alaska in 2004.  More recently, the green alder sawfly was identified in trap samples in nine Washington counties and one Oregon county (Multnomah).  Examination of insect collections at Western Washington University indicates that this insect has probably been present since 1995.  It was first detected in the contiguous United States on understory shrubs in Vancouver, Washington in April 2010.  We don’t know a lot about this insect but we are beginning to tease out how it operates.

green alder sawfly larva
Figure 1: Green alder sawfly larva (photo by Jim Kruse)

How do you identify this critter?
Adults emerge from overwintering sites in the soil or dead wood in the spring and lay eggs on expanding alder leaves.  New larvae are very pale green and 2-3 millimeters long.  Over time, as the larvae mature, they become a vibrant green (Figure 1).  When fully grown larvae are about 15-18 millimeters long, a little more than ½ inch.  The adults look like a small wasp, and the females (males have not been recorded in North America or the UK) have a black head and antennae.  The middle (thorax) of the adult insect is black, sometimes with some yellow or brownish coloration; their legs reddish brown to black and abdomen black with the margins of the segments white to yellow (Figure 2).

green alder sawfly adult
Figure 2: green alder sawfly adult (photo by Andrei Karankou)

Life history
A pre-pupal stage overwinters and pupation occurs in the spring.  After the eggs hatch in the spring, larvae feed on alder leaves through the spring and early summer, then typically drop to the ground to pupate in the soil.  In Europe and recently observed in Alaska, these insects have been reported to also burrow into rotten wood to pupate (Figure 3).  Just another reason not to move firewood interstate.

What about potential impacts?
Not much is known about how this insect will fare on red alder in western Oregon and Washington, as well as other species throughout these two states.  In Alaska, this species has been feeding primarily on thinleaf alder (Alnus tenuifolia).   There is some concern that the feeding of the green alder sawfly, woolly alder sawfly and the striped alder sawfly combined with stem cankers may lead to reduced nitrogen inputs by alders and perhaps alder mortality.

green alder sawfly pupal niches
Figure 3: green alder sawfly pupal niches (photo by Jim Kruse)

In the Pacific Northwest, several insects feed on alder species so these may compete for host foliage and the additional feeding by the introduced sawfly may have a minor effect.  However, the green alder sawfly begins feeding earlier in the spring than other species and could effectively outcompete native species if foliage becomes limited.  Another concern is the native parasite/predator complex: will these make the switch to the new invader?

What to do?
Efforts by federal and state agencies will include trying to delimit the extent of the sawfly’s distribution and encouraging more monitoring as well as research and education.  The US Forest Service point person for this invasive insect is Kathy Sheehan, based in Portland.  She is coordinating the effort to determine the distribution of the green alder sawfly in Oregon and Washington.  They have already set up trapping sites throughout western Oregon in particular.  Eradication is not a feasible option because of the widespread distribution of detections in Washington and Oregon.  The fact this invader can potentially pupate in dead wood is another reason to manage the distribution of firewood and keep it local.

The bright green larvae are distinct.  If you are out and about in your forest, look for these critters on alder leaves and if you find any likely suspects contact Amy Grotta at the Extension office, 503-397-3462, Dave Shaw, OSU Extension Forest Health Specialist (dave.shaw@oregonstate.edu) at 541-737-2845, or Kathy Sheehan (ksheehan@fs.fed.us) at 503-808-2674.  For more information, go to http://www.fs.fed.us/r6/nr/fid/invasives/green-alder-sawfly.shtml.

References
Green Alder Sawfly.  2010.  Forest Health Protection, Pacific Northwest Region, USDA Forest Service.  4 pages.

New Pest in Alaska and Washington: The Green Alder Sawfly-Monsoma pulveratum (Retizius).   2010.   Pest Alert.   USDA Forest Service State and Private Forestry Alaska Region.  R10-PR-002.  2 pages.