Hi

It looks like the start of some brown rot fungi. No need to start freaking out about some fungi in the crawlspace; there's no way the owners will get exposed to it unless the interior of the home is open to the crawl someplace so spore can spread up into the house.

Write it up and recommend they get the underside of the floors treated with some BoraCare. BoraCare is a glycerin-borate mix. You cut it 1/1 with water and apply it with a pump sprayer. It's toxic to all forms of fungi but non-toxic to humans, and it will soak into the wood making it immune to future fungal growth.

Powder-like or not, that soil is giving off moisture - about 11 gallons every 24 hours for every 1,000 square feet. Get the soil covered with a cap sheet after the underside of the floor is treated.

ONE TEAM - ONE FIGHT!!!

Mike