We have an 8 acre lake that is 50% covered in coontail. We are going to spray diquat and cutrine plus together. What is recommended mixture rate per acre?

tank mix 1 to 1 at a rate of 1 to 2 gallons per surface acre. From the book Water Weeds and Algae

One thing to keep in mind that it doesn't really matter how much water you add, but you have to add enough water to cover the one surface acre with the 1 to 2 gallons of chemical. i.e. 1-2 gallons of chemical in 10 gal of water or 100 gal of water it really doesn't matter, but you have to spray that whole tank mixture on the one surface acre.

If it was me, I would do the following:

Take 8 to 16 gallons of chemical mixed with a minimum of 80 to 160 gallons of water to treat the whole pond. I would NOT treat the whole pond at the same time, Kill too many weeds/algae at once, and when they decompose they could create an O2 crash that the fish would not like at all.....