...the soil that in days grow i the yellow powder within days grows into a large, bright yellow 'mushroom shaped' object. it is light and powdery it sits on the top of the soil and is easily removed but keeps returning! any suggestions please!!!

sounds like a poisonous mushroom called Yellow Pleated Parasol ie. Leucocoprinus birnbaumii. Although i aint an expert and thats just a guess. check out the web page linked below

You might have to much moisture around your tree. I would take a sample to your county extension agent