Here is the latest Iowa news from The Associated Press at 3:40 a.m. CDT

DAVENPORT, Iowa (AP) — President Donald Trump and former Vice President Joe Biden are unleashing the kind of verbal attacks that feel more appropriate for the final weeks before Election Day than a lazy summer day about 17 months before voters go to the polls. Biden says Trump is an “existential threat” to the nation. Trump suggests Biden is “weak mentally” and insists, “People don’t respect him.” Both men were campaigning in Iowa Tuesday, and Biden has one more event in the state Wednesday.

DES MOINES, Iowa (AP) — The U.S. Department of Agriculture has lowered its estimate of this year’s corn crop to the lowest in four years, saying wet weather has delayed planting and reduced acres planted and the expected per-acre yield. Production was cut in a monthly report released Tuesday by 1.4 billion bushels to 13.7 billion bushels, the lowest since 2015.

DES MOINES, Iowa (AP) — A study shows Iowa leads the nation in the amount of human and animal waste it produces. Christopher Jones is a scientist at the University of Iowa. The Des Moines Register reports that Jones’ study shows the state of 3.2 million people and total livestock population of nearly 110 million produces as much manure as a human population of 168 million. His study indicates pigs are responsible for driving the state to the top of the rankings.

NEBRASKA CITY, Neb. (AP) — A judge has ordered a mental evaluation for an Iowa man charged in the deaths of his former girlfriend’s parents in Nebraska. Sioux City, Iowa, station KTIV reports that the Nebraska judge on Monday ordered the evaluation for 36-year-old Brindar Jangir to determine whether he is mentally fit enough to stand trial. Jangir was arrested in March in the shotgun deaths of 56-year-old Randal Grimes and 51-year-old Annette Grimes in Douglas, Nebraska.