Aerial spraying of glyphosate herbicide, one of the most controversial methods of coca eradication, has taken place in Colombia exclusively because of that government's willingness to cooperate with the United States in the militarized eradication of coca after signing Plan Colombia in 2000. In many cases the spraying is carried out by American contractors, such as DynCorp, using planes and helicopters to spray glyphosate on coca plantations. Aerial spraying has been repeatedly condemned by human rights and environmental activists because of its effect on human populations and local soil and water systems.