CLARKSVILLE, Iowa (AP) — Officials say Butler County has become the 51st Iowa county in which an insect that's killed millions of ash trees has been found.

Officials with Iowa's Department of Agriculture and Natural Resources Department and the Iowa State University Extension services say the emerald ash borer was found in a tree in Clarksville.

Earlier this week, the destructive pest was confirmed in Benton, Buena Vista, Floyd, Howard and Warren counties.

Infected trees usually lose leaves at the top of the canopy and the die-off spreads downward. The trees usually die within four years.

The...