I would check with local beekeeping associations in YOUR area to see what diseases are present. In some areas it is illegal to not treat hives, for example Skep hives are not allowed to be used as they can't be managed. My area has many diseases, but this year I treated with fumagilin b for nosema, and apistan and formic acid pads for varroa. I have a neighbour who doesn't treat his hives for anything. He collected MUCH less honey this year from established hives than I did from packages. Bees can survive without treatments depending on the severity of the disease, but skilled management techniques are necessary to not use treatments, and instead go the route of small cell etc. Read up on the treatments and decide from the facts what you want to use in your hives, or find out the facts about HOW to manage hives without. There is a large body of information on both perspectives on this site, opinions are very divided, but if this is your first year, you might want to stick with what works in your particular area, whether that is medication or not.