That's not easy because a lot of factors influence fungal growth and toxin production include, for example temperature, moisture content, pH, substrate, humidity, competation and interaction between fungi and another microorganisms and aeration. I'm curious too that is there any existing method.
As Tamas mentioned, there are lots of factors and as far as I know, no sensitivity analysis has been done so far...so no clue on which are crucial over others.
However models and methods are under development in Canada. Maybe the attached paper could give some cues?