MITCHELL, S.D. -- The first confirmed emerald ash borer infestation in South Dakota has been discovered in northern Sioux Falls, bringing the tree-killing beetle to within 70 miles of Mitchell.

Ash trees make up almost a third of the trees planted in South Dakota communities and also are also common in windbreaks.

Insecticide to treat ash trees can be expensive, Mitchell Parks Supervisor Steve Roth said Wednesday, and the city lacks a formal plan for dealing with tree deaths.

Authorities have warned for years the invasive insect responsible for killing tens of millions of ash trees in 32 states would spread here.

State Secretary of Agriculture Mike Jaspers implemented an immediate quarantine Wednesday to slow the beetle's spread.