I just came across a new Forest Science Fact Sheet publication by Dave Jackson of PSU on the ecology and management of ferns. If you're dealing with ferns, this is a great resource. I've pasted the first paragraph below, and linked to the full publication. The publication is developed in the context of Pennsylvania's forests, but the message and content has application throughout the region.
[from the publication]...Areas of hardwood forests in Pennsylvania, across the Great Lakes region, and throughout the Northeast contain dense understories of fern, including hay-scented fern (Dennstaedtia punctilobula Michx.), New York fern (Thelypteris noveboracensis L.), and bracken fern (Pteridium aquilinum L.). These characteristic fern understories have made Pennsylvania famous for the picturesque beauty they provide to our forests. Most people don’t know that these dense fern understories are often biological deserts, lacking plant and wildlife diversity and providing little wildlife food or cover. Fern understories also interfere with the regeneration of hardwood forests, threatening their sustainability across the region.
or this URL
UPDATE - 07/16/2020
Dave gave a highly informative webinar on 7/15/2020. The archive for that will post to www.youtube.com/ForestConnect at this link (copy and paste this or use the hot link https://youtu.be/NYnSuLvXRco)
The fern fact sheet is above. Here is a pdf on how to calibrate a backpack sprayer
In addition to calibrating your backpack sprayer, you need to know how to mix your herbicide concentrate. It is a simple process, with a bit of math, that uses the formula V1C1=V2C2...see the fact sheet that follows, or linked here.