edit: (this post is a response to OP talking about fungal issues in WWP in general, not related to fungus/mold on top of soil)
I want to ease your fears about WWP having "fungal issues" a little bit. Most pine species (whether five needle or not) in the western US have within their populations some degree of stress from fungal issues. Western white pine, whitebark pine, lodgepole pine, etc. But when you're in complete horticultural control of a pine, you can reduce or eliminate your risk.
A lot of the fungus-induced deaths in WWP + whitebark result from a stack of accumulating stresses: First they get weak, then they're attacked by beetles, then the beetles import the fungal spores en masse into the interiors of trees. Combinations of regional warming and/or high-intensity fires (as opposed to low intensity beneficial fire) that modify the environment then add to the problem and also reduce recruitment (i.e. seedlings that would otherwise be cooled by a denser canopy get roasted in a hot dry wasteland). When you read about WWP you're mostly going to run into literature that is concerned with this dynamic in the wild.
Wild conditions don't resemble the horticultural setup of a WWP / WBP / LPP / limber / etc in a bonsai garden in the Pacific Northwest because you control so many factors that can avoid that stack of stresses getting established in the first place.
You can have good success if:
- You're caught up on what kind of potting pines prefer to be recovered and grown in -- pumice is insanely cheap in the PNW and a grow box or pond basket isn't hard to find or build. Pines roots want to breathe air. Five-needle and high elevation pines in general take much longer to grow roots, so when choosing media you need to choose for longevity and not a preconceived notion of "trees eat dirt therefore I need some dirt in there". The most superlative health results I have with pine are in pure inorganic volcanic media. Look at what every professional who handles very expensive yamadori in the western US pots high elevation pines into and you will find pumice.
- You grow in full sun
- You don't go wild with fertilizers or biological additives without understanding what that might do to the root/soil environment when there still aren't that many roots
- You're there to watch for insect attacks and maybe apply things like lime sulphur to kill off eggs and spores in the dormant season if there is a concern
- You follow the rule #1 with pine bonsai which is: Let them build up physical mass and obvious signs of vigor, acceleration, momentum before coming back to work on them
Keep the following thought in a time capsule IF you do end up having a WWP turn brown after collection:
A collected WWP is a million times more likely to die due to poor recovery practices and poor potting than from a fungus. The very first WWP I collected didn't survive, and at the time I remember reading about fungal issues. In retrospect years later, it's blazingly obvious what I did wrong (crap potting, overly-shady recovery location). Collecting young individuals of western pines should technically be low risk as long as you have all your pine horticulture checkboxes checked.
Keep em in the sun, don't move them much or at all, don't let them get bit by overnight freezes until they've had a full summer+fall to grow new roots, don't water them too often, don't wire/work/prune/etc for a couple years and you should be a WWP grower in no time
.
