Farmers are turning to an old technology this year to control weeds in their fields. Dicamba has been around for about half-a-century. It is a corn herbicide, but soybeans have been modified to tolerate it. This was done because so many weeds have modified themselves to resist being killed by glyphosate, commonly known as Round-Up.

The primary problem, says University of Illinois Extension Weed Scientist Aaron Hager, is waterhemp.

This inconsistency makes the timing of dicamba applications extremely important. Without a doubt, says Hager, most post applied herbicides are going to do a better job of controlling a full suite of weeds in a field when the weeds are less than three to four inches in size.

It is possible for the weeds to recover, flower, and produce seed. And that, says Aaron Hager, is something to avoid.