A new crop year is a chance for clean fields
Now that grower meetings have slowed down and you gear up for field work, let me review a frequently asked question about weed control options for 2013. My first response to questions about what to do this year is a question in itself. I ask what weed control program was used the previous year. The common response is: a preemergence herbicide applied at planting followed by glyphosate and an in-season contact herbicide. Of course, the drought had major effects on the performance of your preemergence herbicides in 2012. But whatever let-downs we might have suffered last year, we have to recognize that managing herbicide resistant weeds in the future will rely heavily on the proper use of preemergence herbicides. So if your preemergence herbicide was a flop in 2012 please don’t give up in 2013.
For weed control in 2013, I have a few themes for you to consider. With corn or soybean we must start clean with herbicides or tillage. If you plant your crop into weeds you will have weeds all year. Our options for weed control after the crop is planted are limited. Controlling annual weeds like marestail and giant ragweed before we plant our crop can save you a headache during the growing season. To combat these two problematic weeds, 2,4-D or Dicamba can be used prior to planting either corn or soybeans. 2,4-D or Dicamba provide challenges in themselves. Plant back restrictions following these herbicide range from 7 to 30 days (consult label for specific restrictions).
If you are not willing to use 2,4-D or Dicamba in a burndown situation, there are a few other options. Paraquat can be effective on small weeds. Paraquat is a contact herbicide and needs to have excellent coverage of the weeds to get control. Sharpen (BASF) herbicide can also provide excellent control of marestail and giant ragweed. The organic matter of your soil affects the plant-back intervals following an application of Sharpen. Regardless of what herbicide or tillage option you choose, make sure that you start clean.
Choosing the right preemergence herbicide for your farm will depend on the weed spectrum you have in your fields. Just because you have a program that works on one field doesn’t mean that it will be the right program on another field. Programs need to be developed on a field-by-field basis. The Today’s Farmer Agronomy Guide can be very useful for determining which preemergence herbicide you would like to use in corn or soybean based off of the weed spectrum in your field. However, our local agronomist can help you develop a whole-farm weed resistance plan, which will be tailored to your needs.
When we talk about soybeans we must talk about overlapping our residual herbicides to get ahead of the glyphosate-resistant waterhemp and Palmer amaranth. We must get in the mindset of applying our herbicides on bare ground. Generally, most of the commonly used preemergence herbicides will be effective for around 30 days. There are a lot of factors that influence the degradation of herbicides and can vary their effectiveness. So we need to have another preemergence herbicide applied before the first residual herbicide is ineffective. For example: if we apply our first preemergence herbicide on May 1, by June 1 we need to have our next preemergence herbicide applied and hopefully activated by a rain before the first preemergence herbicide is no longer effective. This will provide weed control further into the growing season giving you a greater chance of success.
In corn, a lot of growers talk about using a one-pass program. That is fine if you are scouting your fields and willing to come back with another postemergence application. However, I find that a lot of people plan on a one-pass program and never scout their fields. We had several calls last fall that corn was clean for eight weeks, but when the combines pulled in the field it was weedy. This could have been avoided by scouting. If you are planning a one-pass program scout your fields every seven to 10 days for escaped weeds and other pests that may be present. I like a two-pass program: a preemergence herbicide applied at planting and, 30 days later, another preemergence herbicide applied to extend weed control further into the season.
Regardless whether it’s a corn or soybean crop, it is critical that we keep the crop weed-free early in the season. Early season weed completion is detrimental to your yields.
Scouting your fields every seven to 10 days can save you a lot of headaches later into the season. Getting in the field means you see weed escapes and can treat for them, but it also means you see the disease and insects that can really affect yield. There is no replacement for scouting your fields. MFA’s CropTrack is a scouting program that helps you determine pests that are present and when crop management tactics are needed. Visit your local MFA and see if this program is a fit for your operation.
Dr. Weirich is director of agronomy for MFA Incorporated.
Read more by Dr. Weirich HERE.