Improve Corn Herbicide Programs through Effective Weed Scouting

By: Mark Waddington, Bayer, Selective Herbicides Product Development Manager
Resistance is changing effective weed control and weed scouting.

As the popularity of Roundup Ready crops increased a few decades ago, it seemed the skill of weed scouting proportionately decreased. Then, as weed resistance began to develop, the almost-lost art of weed scouting began a resurgence.

Weed scouting underwent a bit of a renaissance. It became more than just walking the fields to ensure there were no weed escapes and evolved into a year-long routine.

Now, maybe you just finished your scouting or you’re about to head out and scout again. But in both cases, it’s important to know how this year’s weed pressure  informs next year’s decisions.

What to watch for when scouting weeds

There’s clearly more to scouting than a weed. It’s keeping a careful eye on whether weeds are developing resistance to chemistries. It’s being able to recognize if weed shifts occur in the field. It’s identifying weeds at various stages.

When scouting, you may see that certain weeds appear at different times of the year, depending on the growing degree days (GDD) they require for growth. In fact, the National Corn Growers Association (NCGA) offers a helpful reference page for identifying how and why specific weeds show up at different times of the year.


  • Did you know, for example, that giant ragweed needs only 150 GDD to emerge, and it typically shows up before you’ve turned any wheels for spring planting?
  • Waterhemp and morningglory, on the other hand, likely won’t show up until after the corn emerges, as those plants typically need more than 350 GDDs.

Monitor your fields to develop an effective weed control program

As you scout fields this summer, it’s important to note which weeds are appearing when, and keep that in mind as you consider your weed control program year-to-year.

For example, if your field has early emerging weeds, such as lambsquarters, Corvus® herbicide is a valuable tool to control the weeds and help get your field off to a clean start. With two modes of action (Groups 2, 27), Corvus is labeled to control more than 65 grass and broadleaf weeds.

If a weed like fall panicum shows up after your corn has emerged, consider a postemergence application of a product like Capreno® herbicide. With two modes of action, (Groups 4, 27) Capreno provides complete postemergence control of more than 60 grass and broadleaf weeds. For potentially resistant weeds, another solid post option is DiFlexx® Duo (Groups 4, 27) that uses a unique HPPD with the power of dicamba and patented CSI® safener.

Remember that it’s never too early to develop your scouting plan. As Corn & Soybean Digest reported, it is surprisingly easy to forget details from one year to the next, so you should document your scouting year-to-year. But most importantly, remember to use the resources at your disposal to scout correctly and make well-informed decisions in your weed control program for years to come.

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