Just how cold does it have to get to kill those pests?
Many of us like to look for silver linings, and the shining hope of a frigid winter is that overwintering insects suffered more than we did. If there are fewer harmful creepy-crawlers this summer, then maybe that chilly February was worth it.
I can’t speak to how the yellow jackets fared (hopefully poorly), but I do know that our problematic bark beetles—specifically the fir engraver and Douglas fir engraver—took it all in stride. February was hardly a blip on the radar for their sleeping larval selves. It was not cold enough to cause beetle die-off. Thus, expect more browning firs in the months and years to come.
When it comes to winter, beetle larvae are way tougher than we are. They use snow around the base of a tree and the tree’s bark as insulation. The larvae excrete all their stomach contents so the liquid won’t freeze up. Then they fold over on themselves and generate a kind of internal antifreeze. Finally, they wait, able to withstand temperatures of up to -40 degrees.
February’s chill didn’t even come close to that.
This is the characteristic “mining” pattern the Douglas-fir engraver beetle larvae makes when eating the tree’s inner bark. Each beetle has a pattern all its own. Image courtesy of Wayne Brewer, Auburn University, Bugwood.org.
The best hope for temperature-related beetle die-off is to have a hard freeze—below zero—very early or very late in the season. Like in October or now, in March or April. If the freeze comes early, the beetles won’t have yet generated enough antifreeze in their systems to survive; and if the freeze comes late, the larvae will have already woken up with the warmer weather and shed their defenses. However, even in these scenarios, beetles can always fly in from areas that didn’t get as cold.
Thus, it seems, the beetles—and their detrimental effects—are with us for at least another year.
So, in the absence of such beetle die-off, what is a landowner to do? First, keep an eye on the health of your trees. Beetles are opportunists. They’ll go for stressed trees whose defenses are down, and then they’ll spread from there. Cull the diseased trees from your forest to limit infestation opportunities. And while you’re at it, just thin your forest in general. Trees living in competition with one another for light and nutrients don’t have the necessary resources to fend off beetle attacks. Give your trees the room they need to thrive. Finally, if you do have beetle-kill on your property, remove it.
To learn more about beetles, check out these Forest Service documents on the fir engraver and the Douglas-fir engraver beetles. Also, our last post was about bark beetles in North Idaho. Finally, don’t hesitate to give us a call if you have any questions about the health of your trees.
Rampant dieback is evident in area trees, but why?
This year, many of us noticed conifer dieback —especially affecting fir trees—on our properties and in our surrounding forests. The flaring out (or reddening) of so many trees is alarming to those of us familiar with bark beetle infestations elsewhere, including those decimating entire hillsides in Montana and Colorado. Are our tree stands doomed, too?
The thing is, bark beetles aren’t to blame for what we’re experiencing here; they’re just finishing off a job begun by other factors. The fir dieback we are now seeing actually has its roots in a century’s worth of logging, fire suppression, and the introduction of pathogens like white pine blister rust. This all contributes to more grand fir, Douglas fir, and subalpine fir than North Idaho has traditionally supported.
Next, the hotter, drier summers of recent years have stressed out our trees, leaving them more susceptible to diseases and pests. Thus, pathogens that healthy trees can easily fend off are now flourishing amidst weakened “immune systems.”
One such problem is the myriad native fungi that lead to root rot. Doug fir, grand fir, and subalpine fir are the species most susceptible to root diseases, and these diseases alone—even without the beetles—are leading to massive dieback.
Since the fungi responsible for root rot live in the soil and remain onsite through generations of trees, this problem isn’t going away anytime soon. However, even in the face of drought, there are things a landowner can do to diminish the threat of dieback. The first step is to thin the forest so trees aren’t competing for water and nutrients. Twelve to fifteen feet between saplings (more for larger trees) is a good rule of thumb. The second step is to ensure forest diversity, including a majority of trees tolerant of root diseases. These include (in descending order): ponderosa, Western larch, Western red cedar, lodgepole pine, Western white pine, Western hemlock, and Engelmann spruce.
Fir trees sometimes struggle and survive at the brink of dieback brought on by drought and root diseases, but opportunistic beetles exist to finish off the job. In North Idaho, we have over 100 species of bark beetle, each specializing in different conifers and sometimes even different parts of specific conifers. These beetles are a natural part of our forest, but they are flourishing right now due to the aforementioned factors of drought, overcrowding, fir population imbalances, and root rot.
If you notice fir dieback (or other struggling trees) on your property, give us a call. We can provide an assessment of your trees and forest and how best to tackle the domino effect that runs from drought to dying trees.
