Corn Weed Scouting Checklist

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Help your customers stay on track in their cornfields this season. We have friendly reminders for timely weed scouting milestones.

If you’re getting in the corn fields to help your customers scout for weeds this year, you likely know it’s best to start that process early and continue on a regular basis throughout the season. There are some key milestones that will help ensure a corn farmer’s weed control program is as successful as possible.

Scouting Milestones

Brandon Walter, the U.S. product manager for corn herbicides at Corteva Agriscience, has a list of those milestones for you and your customers to hit.

  1. Pre-burndown — Before spring burndown applications begin, you’ll want to get in the fields and see what’s popped up since winter. Knowing which weeds are present can give you an idea of what to expect in the future. This knowledge can also help you plan which chemistries will best control those weeds.
  2. Post-burndown — Wait until the burndown application has had a chance to take effect and walk the fields again. Once you know whether the burndown was successful, you can move forward with future applications. If there are still weeds remaining, you can plan to take other steps to control them — like using tillage. You also can alter your preemergence application plans to get the right solutions on the field to control those escapes.
  3. Postplant — Postplant is a particularly important time to scout for weeds. According to the Iowa State University Extension, weeds can start affecting corn yield as early as two weeks after crop emergence. Knowing this, you’ll want to make sure to plan a timely postemergence application that can clean up any weeds remaining at this time.
  4. In Season — The scouting fun doesn’t stop once postemergence herbicides are applied. You and your customers should still be going into the corn rows at least every two weeks to keep track of any weeds, pests or diseases that might develop.
  5. Harvest — Harvest is an excellent time to scout for weeds. Being up in the combine gives you the height to see above mature corn and look for any weed populations that made it through the season.


Scouting Reminders

Now that we’ve reviewed the key milestones for seasonal weed scouting, Walter has some friendly reminders for performing the scouting itself.

  • Make one or two stops per 20 acres to look for weeds.
  • Note which weed species are present, how severe the populations are (roughly how many of each species) and which growth stage they’re at.
  • Scout for herbicide resistance. If you’re noticing the same weeds escaping the chemistries you’re using while other weeds are under control, resistance could be the issue. If you suspect herbicide resistance, send a sample of the weed to your state diagnostic lab.
  • Scout often, at least every two weeks. Some weeds can grow very quickly and limit yield if they get out of control early in the season. Palmer amaranth, for example, can grow at the rate of 2 to 3 inches per day, eventually reaching up to 8 feet tall. If Palmer amaranth is left to flourish among young corn, it can severely diminish yield. Timely scouting will allow for easier control of those weeds.
  • Take notes and keep them for future reference. Record the weeds you find, the time you scout, the location, the weather and any other details you think are important. Keep these notes for future reference to help inform plans.


Scouting is incredibly important for your customers’ success. Help them keep track of those milestones this season with this handy checklist. And remember: So-called “windshield scouting” won’t cut it. While getting into the fields can be tough and time-consuming, the work is worth it in the end.