You probably can, but more information would be helpful: are you trying to count a particular type of fungus, or total colonies of all fungi? Do you need to be quantitative? Are you isolating them out of soil or what? Is there a problem with bacterial contamination? Are you also interested in Oomycetes? Are you interested only in fast-growing fungi, or are you also interested in slow-growers who might not be detectable on the same medium? Have other scientists tried to do what you are trying to do and described their methods? Every method of counting has its artifacts, so you want to pick a method where the artifacts aren't too severe.