Most herbicides take years to go through the licensing process before coming onto the market and have been researched thoroughly. The toxicity of most common forestry herbicides is less than table salt.

I don't think you could say the same about chicken litter and it's potential impact. Every chicken house you drive by has biohazard signs and warnings about disease, yet we take the litter out and spread it across the county. I know they say the risk is that you may bring something into the chicken houses but I'm not sure how you couldn't also be spreading a disease into the wild as well. This is one factor that all of the experts seem to keep discounting or overlooking.