by Brett Thompson brettt@agpartners.net

With harvest just around the corner, this is a good time to review how effective our weed control plans were this year. When I’m out in the country checking fields, I can’t help but notice that many of the fields have the same two weeds popping up in them, Giant Ragweed and Waterhemp. Waterhemp is already Roundup resistant in our area and the Giant Ragweed isn’t far behind. There were many fields across the Ag Partners territory where a field was sprayed with high rates of Roundup and all it did on ragweed was turn the leaves a little brown. So, what can we do about it in the coming years?

First off, I’m a strong believer that the best way to control some of these troublesome weeds in your soybean fields is to start in your corn. These weeds are much easier to control when you are growing corn than when you are growing soybeans which means less of a weed seed bank when switching a field into soybeans. Many of the herbicides that we use in corn have excellent control of these weeds which equates to a 90% or higher kill of the weeds in the field. Two of the main products that we used this year in corn were SureStart and Resicore. With both products, we have seen clean fields yearlong due to the residual that they are bring to the table.

To control the weeds in the soybean fields, many of us are learning that two passes of Roundup just aren’t doing the trick anymore. So what is going to be the best way to deal with this?

Pre-emerge herbicides are going to be our best plan of attack for keeping soybean fields clean. Whether sprayed on or impregnated, killing the weeds before they come up is going to be key with these Roundup resistant weeds. The main chemical that we have been using for this is a herbicide called Sonic which has been having great results especially when tank mixed with another herbicide called Dimetric. I would encourage you to have a conversation about these products with your agronomist if you haven’t tried them before.

These pre-emerge herbicides provide good/excellent controls of our most troublesome weeds. Which if you recall earlier, excellent is a 90% control. So mid-season they still may need another post emerge pass. The most common product we were using for these Roundup resistant weeds this year was Flexstar GT. Flexstar GT is a contact herbicide, meaning it kills the parts of the plant that the spray solution touches. The key for this herbicide to work is small weeds and lots of water for good coverage of the plants. Another option that many farmers are considering is planting an Xtend soybean variety. The Xtend trait allows us to spray the soybeans with a special formulation of dicamba to control these Roundup resistant broadleaves. In the next few years this is going to become more and more popular because many of the seed companies are putting the trait in all their new varieties.

If we bring all these together, a good corn herbicide program is crucial in controlling weeds in soybean fields. Killing weeds before they come up with a pre-emerge chemical will help control weeds throughout the growing season in soybeans, and that sometimes a rescue pass of a contact herbicide or Xtendimax may be needed to help control these problem weeds.