Question
My KY Master Gardener study group has a difference of opinion on a study question.  Will you be so kind as to lend your expertise?
Many fungal pathogens thrive in a climate in the northern KY (near Cincinnati) area. This is because:
a. Humid weather & moderate temperatures
b. Very cold winters & very hot summers
c. Diversity of native plants
d. All of the above
I would think b. would be true as in the case of apple scabs which overwinter & need to hot & dry summer temps. I would think c. could also be true.  
Thanks for your help!

Answer
Unfortunately it is not as simple as what you are asking. All infestations need a host, the spore source and the right environment to infect a plant. This is normally called the Disease triangle. The right moisture and temperature at the time the spores are present and if a host is present then infection could occur. But all this differs by the fungi. Apple scab spores are on the fallen leaves and are produced in the spring during leaf out and cool moist conditions but also later in the year on green leaves on the tree.  Here is a web link to a much more detail account of fungi infection as it varies by fungi. http://www.apsnet.org/edcenter/advanced/topics/EpidemiologyTemporal/Pages/Diseas
I hope this helps and is not too confusing.