Since the 1960’s farmers have been using herbicides to control weeds. Frankly, herbicide formulations haven’t changed that much and the weeds have managed to find ways to adapt. Todd Gleason has this four step plan from the Univesity of Illinois to control them in corn or soybeans.
Some weeds have become resistant to the herbicides farmers use to control them. Others have lengthened their germination period, emerging later in the season, avoiding early spring control methods. University of Illinois Extension Weed Scientist Aaron Hager has a four step plan farmers can use to maintain a competitive edge in corn or soybeans. It starts by planting into a weed free seedbed.
Quote Summary - It is easy to achieve a weed free seedbed by either replant tillage, burndown herbicide or a combination of those two. Given the challenges of weather and of resistant populations it is advisable not to plant into existing weed populations or any green vegetation without adequate control ahead of time.
Step two in the plan is to select an appropriate residual herbicide. Be sure it provides very good control of the most problematic weed species in a given field. Pay attention to the label, says Hager, and always apply the recommended rate for the spectrum of weeds in the field.
> Quote Summary - The third step is to make timely post emergence applications. Base those on just not the number of calendar days after planting, but rather base those post decision on adequate scouting. So, return to the fields about two weeks after crop emergence. Scout the fields and determine the weed size, crop development stage and make the decision on a timely application of a post herbicide.
The final and fourth step is to go back to the field seven to ten days later and evaluate how well the post emergence herbicide application worked. It may be that another germination of a weed species warrants a second application. This won’t be know without a return trip.
If we fail to go back and look at how well the product performed, or the level of crop injury we see soon after that application, we could have some very significant challenges later in the growing season.
The days of set-it-and-forget weed control have ended. Todays farmers must scout fields for competitive weeds before during and after the growing season.