On Juniperus scopulorum in southern Utah, USA, R.G. Krebill found a black stroma (sclerotium) extending from in the soil to well up into the branches and small twigs giving the bark a fire-charred appearance. It is several centimeters long and up to 2 cm thick (mostly less). It’s composed of much-branched chains of cells, each cell about 10 mm long, 8 mm  wide near the tips of chains but gradually increasing to 12 mm wide (measured cross-chain) back from the tips. The terminal cell is up to 16 mm long, presumably just before dividing. The brown (by transmitted light) cytoplasm shows no clear contents, the walls are darker brown.

This seems to  fit Helicobasidium/Rhizoctonia in general but I don’t find reference to big, black sclerotia like this on conifers. Helicobasidium/Rhizoctonia is blamed for rot in pines, I think basal on the trunk (& root?). R. crocorum, which goes under several names, is possible, but the sclerotium doesn’t seem right.

I can mail a specimen if someone knowledgeable would look at it.

Roger Peterson

Santa Fe, New Mexico