Plant patents didn't cover crops that had to be replanted annually, so the only licensing restriction they imposed on farmers was that they had to get certain varieties of fruit trees and other similar plants from approved breeders (and honestly, I don't think most of them were even that expensive). In 2006 a company did begin using its plant patents on a variety of apple called SweeTango to force farmers to agree to a restrictive contract that forces them to only sell their produce through the apples through them and pay ongoing royalties, but that practice was previously unheard of.