Re: White fungus in garden soil
Much of the planet is basically covered in a fungal mantle; looking at the entire history of life here it would be the Dinosaur Planet but otherwise it's the Fungus Planet. So, there is no way to know from the information here what kind of fungus you have and what effect, if any, it might have on your plantings.
Sampling your soil and having it tested might be a good idea. This will give you a picture of its current suitability for growing crops, as far as nutrients, pH (whatever you have it tested for) are concerned. Try your state Cooperative Extension Service branch office or web site for assistance with this.