Another rule in the playbook is start with a clean field and keep that field free of weeds.

“When you spray a field and 5% of the weeds remain and don’t die, you want to deal with those weeds immediately,” says Steve Muhlenbruch, agronomy manager for Dows Farmers Cooperative, Dows, Iowa. “We still have options available to us, but we don’t want those weeds to get out of control.”