Gosh,, you're lucky if you can use preservative at all.

Out "here" buyers will NOT touch hay that's been sprayed with preservative. Many won't buy if I spray with 24D amine and a few ounces of banvel to control weeds.

They freak out thinking their animals are being "POISONED" !!

BTW...  This is one of the "side benefits" of the general population being several generations removed from Farming !!  

Most know 24D is one of the safest weed killers to use. It is only a synethic growth hormone with a very short 1/2 life.  Banvel is nastier, no doubt,, but 2-3 oz per acre isn't anywhere approaching any toxic level. BUT the public doesn't believe the science,, they believe all the HSUS, earth first, etc.. emotional BS those groups are shoving down the general public's throats.