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Posted 26 March 2015. PMN Crop News.

Game Planning Against Weeds

Teamwork and tips are key to managing resistance

Source: United Soybean Board Press Release.

Chesterfield, Missouri (March 11, 2015)--Herbicide-resistant weeds get a lot of coverage in today’s agriculture publications. However, resistance is not new. It’s a recurring issue we’ll need teamwork to manage. Universities and seed and crop-protection companies work hard to develop traits to control and prevent resistance. As retailers, we do our best to develop sound weed-control programs to take advantage of this work. And we’re doing better in delivering educational programs to explain the importance of resistance management. Going forward, it is critical that we diversify herbicide modes of action. I hope that you have already taken that step on your farm.


When building a program to manage herbicide-resistant weeds, there are several things to consider:

1. Target weeds

As you develop a resistant-weed-management plan, get to know your enemy. A list of your problematic weeds is a place to start: Scout your fields. What is your most common or frequent weed? Is it resistant? That gets you the information you need for a sound weed-management plan.

2. Cropping plan

The days of applying just glyphosate are long gone. One reason glyphosate was overused was its lack of residual activity meant carefree crop rotations. Glyphosate’s lack of residual activity meant that crops could be planted without consideration of the herbicides used previously. However, many of the the residual herbicides we use today have longer residual activity, requiring a certain amount of time before the next crop can be planted. We need to have long-term cropping plans.

3. Soil characteristics

Most residual herbicides are rate-dependent in relation to soil type and pH. This means they will be most effective when applied at the full labeled rate and at the recommended weed size.

4. Apply the labeled herbicide rate at the recommended weed sizes

When it comes to an effective herbicide program, multiple residual herbicides should be applied sequentially before the weeds emerge. Many university weed scientists call this “overlapping residuals.” If you have weeds present at planting, they will be hard to control as the crop grows. Once you have your pre-emerge herbicide in place, you should commit to a plan to cover the field again with an overlapping residual 24-30 days later. The goal is to get the second residual out before the first one becomes ineffective.

5. Have a whole-farm plan

Develop a plan for your whole farm for the entire year. This gives you better time management and weed management. Whether it’s through tillage or a good burndown, you need to plant into a clean seedbed. Throughout the growing season, scouting and managing weeds as they appear is important. At harvest, clean out equipment in-between fields to prevent weed seeds from spreading.

Your cropping and weed-control plan is important, but don’t blindly follow it. Adjust when needed. If you aren’t fighting resistance yet, you will. Contact your input provider for more resistance-management information.