notice how the stem attaches to the cap, very different than the deer mushroom. The shiitake stem is fuzzy like and multi colored. The deer mushroom stem is a smooth white stem larger at the bottom of the unit and concave narrow attachment on the cap. The deer mushroom stem will snap very easy. Once a deer mushroom appears on a shiitake log, I remove the log from production, even-though shiitakes can still be harvested in future fruiting cycles. So we caution mushroom identification before harvest.
These two photo's are a stem mushroom that can grow on a shiitake log. It is known as a pluteus cervinus, also known as Pluteus atricapillus and commonly known as the deer mushroom. It is found on rotten logs. These mushrooms can be gray, brown and white.. It is edible but undesirable. Mycological characteristics consist of gills on the hymenium, cap is flat or umbonate, hymenium is free, stripe (stem) is bare and spore print is salmon to reddish brown.
The green mold that is seen around the edge of the log is known as Trichoderma.
This fungi can be deadly to a shiitake log that has just been inoculated, but a establish shiitake log can hold its own against this mold with little damage to mushroom production. There is no real fix for the mold on the log.
These photo's are other molds and weed fungi that can grow on logs that pretty much out of the shiitake log growers control. The best defense is to keep the log from lay on the ground and out of direct sunlight as much as possible. The inside of the log should be kept moist by flipping end to end month to month and hydrate by soaking in water over night. In general you want to get the bark dry and inside of the log moist.