Aerial spraying to kill Canada thistles in Badlands National Park has been completed for the year.

Park officials say the spraying was needed because the Canada thistle is a noxious weed that otherwise would spread and interfere with the natural ecology in the park and nearby land.

Badlands National Park has about 64,000 acres of wilderness, and a commercial helicopter operation sprayed more than 5,000 of those acres in July. Outside the wilderness areas, all-terrain vehicles were used to spray another 150 acres infested with Canada thistles.