BEND, Ore. — The U.S. Forest Service is planning to cut down hundreds of ponderosa pines that were killed by an herbicide applied along a highway in Central Oregon. The federal agency is taking public comment on a plan to remove the trees along a 12-mile stretch of U.S. Highway 20 near the city of Sisters, The Bulletin reported Thursday. The Deschutes National Forest trees were likely killed by an unhealthy dose of the weed-killer Perspective, which contractors working for the Oregon Department of Transportation first applied around 2013, forestry officials said. The herbicide was administered to kill broad-leaf weeds and other plants that pose fire dangers.