Dear Ross,
You may have a couple problems going on with your honeyberries (or Haskap as they're known.  I want to refer you to this fact sheet from Utah State Extension:  
Haskap in the Garden | USU
A relevant paragraph from that fact sheet is:  

These plants are native to very cold regions and experience scorching, mildew and pre-mature leaf drop when grown in warmer climates (above zone 6). Plants of Russian origin are more susceptible to summer injury in warm regions. In areas with intense summer heat, the Japanese varieties are better suited for planting. However, in colder, higher-elevation areas, the Russian types may be better adapted.

You may not know whether your plant is of Russian origin or Japanese origin, but summer injury from heat, sun, and mildew could all be contributing factors. Hamilton County is in growing zone 6B, which is the southernmost zone that the plants can tolerate.  When you look at the fact sheet, check out the recommended varieties and care for Haskap.

Iowa State Extension has a succinct fact sheet on honeyberries as well, along with recommendations of varieties:  
What are honeyberries? | Yard and Garden (iastate.edu)

Finally, the University of Wisconsin has a nice background fact sheet:  
Honeyberries – Crops and Soils (wisc.edu)

Everything I've read says that honeyberries are relatively free of insects and diseases and are great for cold climates.  But the growing conditions seem to be a key factor.  You can try changing their location in your yard to a spot where there is good air circulation to help prevent mildew and other fungal infections.  If you go the route of trying fungicides, that will be a constant battle.  But there's nothing you can do about southwest Ohio's hot and humid summers.  

Best of luck.