Root Rot: Digging Deeper

It’s worth taking a closer look at the root rot affecting our firs

In a previous post, we looked at the dieback affecting area fir trees in more general terms. Now, it’s time to get up close and personal with a more specific ailment: root rot.

root rot
Young grand firs tend to succumb quickly to root rot, browning out before any needle loss occurs.

This issue is at the root—pun intended—of fir mortality in the region. Douglas firs and grand firs are highly susceptible to North Idaho’s three most prevalent kinds of root rot: annosus, Armillaria, and laminate. All three kinds of rot are likely present in a single stand. They may even be present in a single tree. The fungi spread easily between trees; all it takes is for an infected root to make contact with another tree’s roots underground. And the diseases can live for up to fifty years in a dead tree’s stump or roots. They can even survive fire.

This perniciousness leads some to refer to root rot as a “disease of the site.” This means it doesn’t leave when infected trees leave. It remains. And it spreads, up to a foot outward from the center of infection each year.

Telltale signs of infection include: crown thinning, foliage discoloration, reduced growth, pitching out at the base, and production of many cones known as “stress cones.” But here’s the scary part: Only half of the trees currently suffering from root rot are presenting above ground symptoms. Our trees are dying, and we don’t even know the half of it. Quite literally.

What’s a landowner to do?

Sadly there is little we can do to eradicate root rot. It’s here to stay. Homeowners can try to protect still-healthy firs on their properties by removing sick trees and any firs whose roots might be in contact with the infected ones. However, seeing as half the trees suffering root rot aren’t expressing symptoms yet, it seems we can only address the problem after it’s too late. A large tree might not become symptomatic until over fifty percent of its roots have been destroyed.

root rot
This dead grand fir is ringed by its fallen kin, but the surrounding larch are unaffected.

One method that some homeowners and foresters are experimenting with is simply eradicating all fir trees. Then they start over by planting root rot resistant larch and pines. Such an approach is not ideal in the short term, but it may be our best bet for forest health in the long run.

Unfortunately, there’s not much we as arborists can do to administer to your firs…beyond treating sickly ones at the base with a chainsaw. However, if you have any questions or want an assessment of your trees or forest, don’t hesitate to give us a call.

For more information, visit these sites addressing root rot: