Fungus in Soil??

I have a Lemon tree I grew from seed 5 years ago, it is very special to me. It has some sort of white fungus growing in the soil. (its in a pot) And I have a wooden stake that supports it, and on the bottom of it, there is some fungus as well. How do I get rid of this, soap and water seems to not be helping, and its losing a lot of leaves, and so is another one with it.

 

can anyone help me at all?

 

I would try sowing a little lime in the soil. Worked for me on saving a willow.

 

I would try transplanting it and put some phosphorous in the soil to promote rooting, I think it might have powdery mildew, spray the foliage with a fungicide with an active ingredient of chlorothalonil