Residual herbicide in soybeans sets stage for successful glyphosate application

By Rhonda Kupke

DuPont Retail Account Manager

If you remember when soybeans were considered a low-maintenance crop on the High Plains, you may be getting old. Just consider a few of the factors that can determine the difference between high yields and mediocre ones:

--Variety selection;

--Tillage practices;

--Row width;

--Planting date;

--Asian soybean rust threat;

--Weed resistance;

--Rising fuel costs.

Add in unpredictable weather or unexpected insect infestations, and making a crop can really become difficult. Growers in my area of western Nebraska have shown that they are up to the challenge. Last year, they averaged between 60 and 65 bushels per acre under irrigation.

Regardless of where you farm, the key is to go into the season with a clear idea of what you would like to accomplish and how you plan to do it. One area where growers can have a positive impact on yields and profits is by applying a residual herbicide ahead of glyphosate. Without herbicides, U.S. growers would suffer annual yield losses of nearly 290 billion pounds and income losses of more than $13 billion, according to a study by the Crop Protection Research Institute. The economic benefits of herbicide use include a $7.7 billion reduction in weed control costs.

Research shows that weed competition early in the growing season may have a greater yield drag than weeds that emerge after the crop is established. This "invisible" yield loss can reach 2 or 3 bushels per acre in some fields, according to weed scientists. Early weeds can even aggravate insect problems by providing a place to lay eggs.

That's why controlling weeds early with a residual herbicide only makes sense. Don't get me wrong--glyphosate is still an excellent tool to use. However, it should not be the only one in the toolbox. Burning down existing weeds with a residual herbicide provides a nice, clean seedbed for planting. It also broadens the control spectrum versus glyphosate alone and helps with resistance management.

Perhaps most importantly, it also creates a wider application window for the first glyphosate application. With early season weeds in check, you can spray when you want, not when the weed pressure dictates. That can become especially important during rainy weather. Many growers have found they can delay their glyphosate application until just before layby.

There is no "one-size-fits-all" program for residual weed control in soybeans. Most growers in my area would like to include a residual herbicide in their programs but have to find what works under their soil types, pHs and tillage practices.

Don't be afraid to try new things. I encourage you to experiment with residual weed control this spring and see what works best with the way you farm. Remember, the goal is not to have the cleanest-looking field from the road but to produce the most soybeans--and profits--at harvest.

Best wishes for a successful 2006.

Editor's note: Between the Rows is brought to you by industry leaders in order to keep you informed about current growing conditions, regional practices, important management issues and environmental concerns. Rhonda Kupke, Grand Island, Neb., is a Retail Account Manager for DuPont Crop Protection.

Date: 2/22/06