No, it doesn’t have a disease.
Yes, “EWWW” was my first response when I looked underneath the frond and realized I was touching the spots. 
Actually, my fern is fertile. Yay!
The spots under the fronds are called sori (plural). Each sorus (singular) is filled with spores. When there is enough moisture, the spores will release and do their thing in the soil (fertilize itself; each spore contains male and female parts). Hopefully next year I will have more ferns.
Ferns do not produce seed, flower, nor fruit. They, like mushrooms, reproduce by spore. Isn’t that neat! This has been your daily dose of biology class. 
Here is a close up photo of the sori.
From on top, you would never know what’s going on underneath. This is my first year growing ferns, I hope to fill the shady spots along my fence will baby ferns.
What do you have growing in your yard?
