RE: don't fertilize a pine tree
portable ladder; did you pour the fertilizer right on the tree trunks? Did the entire tree turn brown or just selected branches? I fertilize my trees and have never lost one due to that cause. Was the soil very dry when you fertilized? If the area was heavy in grass that should have cut down on the amount left for the tree. I'd water heavily and hope you can flush the soil.
Simazine is a good choice as a herbicide if you can get it or Roundup if you shield the trees.
Dan O.