New Thoughts on Old Weed Management Options

Make no mistake, the Roundup Ready system in both corn and soybeans is poosibly the greatest boon to farming over the past 20 years. Still, it was only a matter of time until nature would greet us with some form of resistance, as is happening now. Soybean farmers need to be vigilant when it comes to weed resistance to glyphosate herbicides like Roundup® and Glyphos™.

Ryegrass and marestail have been documented as exhibiting resistance to glyphosate and there is some strong evidence that waterhemp, common lambsquarter and giant ragweed are showing signs as well.

Let’s look at a few simple techniques that growers can start using right away in their soybean program to help minimize weed problems in this Roundup Ready era:

1. Start clean- Stay clean.
   By starting the growing season weed-free in your soybean field, you can help eliminate your reliance on glyphosate alone. If a farmer is no-tilling, the use of a proper burndown, consisting of more than just a glyphosate product, is essential. There is a wide range of burndown products that can be used with glyphosate or by themselves. If you plan to use tillage, then get rid of that temptation to just use glyphosate and add some other modes of action into the mix.  The old “yellow” herbicides (Treflan, Prowl, etc.) are fairly reliable for grass control and will also help with many small-seeded broadleaves. Keep your fields clean by using the right rate of glyphosate at the right time. Also, don’t forget the cultivator. It might be time to drag out that old beast put it back to work. Better a little bit now than a lot later!
2. Right rate- Right time.
   The Roundup Ready system for both corn and soybeans might just work too well! For instance, the labeled rate for most annual weeds on the Roundup WeatherMAX label is 22 ounces/acre when the weeds are between 3″ and 6″ high. However, most farmers will tell you they have had great success using that rate for weeds up to twice that height and there lies the problem! We start to rely on a low rate of glyphosate to control weeds that are taller than the labeled height. Therefore, we are artificially selecting those weeds that have a tendency toward resistance just so we can tell our friends and neighbors that we only sprayed our soybean fields once and did it at the lowest rate possible. Don’t fall into that trap!
   
3. Rotate herbicide programs.
   Growers should use glyphosate crops in farming rotation where they have the greatest economic and management value. Rotating between glyphosate-tolerant crops and conventional crops or crops with other types of herbicide resistance (LibertyLink® for example) can help prevent weed resistance.

Make it a priority in 2009 and beyond to address weed resistance to glyphosate herbicides. It will definately benefit you in the long run. For more information on weed resistance issues, contact our Latham Seed2Soil® specialists, or leave us a question in the comment box below!