Hosts of Porodaedalea pini

The last few weeks have been a real eye-opener with respect to Porodaedalea pini. In my four years in the Colorado area, I had only seen the stem decay fungus on Engelmann spruce (Picea engelmannii). However in the last two weeks I have seen it on lodgepole pine, subalpine fir, and Douglas-fir.

The new finds were outside my usual stomping grounds. I was up in the northwestern part of Wyoming, on the Shoshone National Forest between Yellowstone National Park and Cody, for cruiser training. There we were in a stand with a lot of defect and decay. In addition to fantastic punk knots on spruce, we found a lodgepole with small, obscure punk knots. We felled the tree and found mostly brown discoloration and very early stages of decay for about the first 15′ of the stem. Nowhere was there more advanced decay. Only when I split a piece longitudinally could I find a few white pockets and zone lines that we typically see with Porodaedalea pini. Later we found a Douglas-fir with punk knots – the dead branches tended to pull out easily and had the golden-brown color of the mycelium on the rotted ends.

Then, last week in hazard training in Frisco, Colorado (near Breckenridge) we found several subalpine fir (Abies lasiocarpa) with the disease.

Of course the pathogen has a wide host range, but these are the first times I have personally seen it in anything but spruce. In both areas, the fungus was apparently most common on Engelmann spruce. In southern Colorado it appears to be more restricted to spruce and these other hosts must be rare.

Stem Decays