By Darren Hefty
Nobody thought it would spread this fast, but weed resistance to glyphosate and other herbicide families is moving across the country quickly and becoming a larger issue on more acres each year. The question is not IF it will affect your farm; the question is WHEN and more importantly WHAT you can do to keep resistant weeds from hurting your crop production and your profitability.
Multiple Sites of Action
When you think about diversifying the number of different herbicide products you use on your farm, you probably think about using different modes of action. This is good and is how most people have always looked at herbicides. Find a different family of herbicides to take more than one shot at each weed. However, you need to go further than this because different modes of action may have the same site of action. What you really need is a new SITE OF ACTION. What’s the difference?
SITE of action designates where the herbicide actually kills the plant. More than one mode of action may actually work on the same site. If you chose two different modes of action that both work on one site in order to control a weed with resistance at that site, you have a problem. If you were hitting the weed in its stomach and its knees at the same time (to use human anatomy as a visual), it would be pretty hard for that weed to defend itself, so focus on the SITE of action rather than just the mode. Look for more discussion and specific charts to help you with Site of Action coming up at the Ag PhD Winter Workshops.
Layering Residuals
A concept that is starting to gain momentum is something we’ve been talking about for years. Rather than putting all your eggs in the basket of one pre-emerge residual herbicide, why not use more than one? Plus, if you want your residual to last longer, why not use residual herbicides post-emerge to extend your window of soil residual control of problem weeds? With crop prices where they are today and the amount of yield potential you can save by improving weed control, it’s pretty easy to justify investing a few more dollars in residual herbicides with multiple sites of action to achieve more yield, better weed control, and more piece of mind and flexibility.
Keep Your Best Post-Emerge Options Open
It’s important, though, to plan out your attack in advance. Getting an experienced agronomist to help is key. One of the biggest things to watch out for is not to use your best post-emerge option as a pre. For example, if FirstRate is your best post-emerge product for something like Roundup-resistant giant ragweed, don’t use Authority First or Sonic as your pre-emerge choice. If you do, what are you going to use to clean up any escapes? There aren’t many options. Instead, use something like Authority MTZ or Fierce (when it’s labeled in your state) or even Treflan plus Metribuzin. That may not be quite as good as Authority First or Sonic to begin with, but you’ll be fairly close. Then, post-emerge you’ll have the option to go FirstRate plus Flexstar and do a bang-up job on the escape giant ragweeds that get through your pre or the ones that germinate later in the season.
LibertyLink Crops
If Roundup-resistant weeds are a big concern for you, switching to LibertyLink soybeans gives you the option of spraying Liberty post-emerge. We’ll talk more about making Liberty work its best as the season gets closer. If you’re concerned about getting the Liberty you need to protect your crop, order your soybeans now and order two shots of Liberty at the same time. Having the Liberty available for canola, soybeans, and cotton is Bayer’s priority. While I can’t guarantee anything, I’ll be shocked if you order Hefty Brand Soybeans from us in December and we can’t get you covered on the Liberty herbicide.
Follow best management practices if you have weed resistance in your area. Read through these recommendations again as you plan for 2013, and visit with your agronomist to address your specific weeds, soils, and history.