Evaluate weed control in soybeans now

By Nathan Winter, University of Minnesota Extension

According to David Nicolai, regional Extension educator,crops, out of Hutchinson, now is a good time to evaluate the success of weed control programs in soybean fields. Due to this year’s dry growing conditions many soybean fields have open leaf row canopies. Thus, there has been more sunlight available down to the soil level resulting in more mid- to-late season weed growth. Even fields which received two applications of a glyphosate herbicide are exhibiting above average weed growth and weed density. Many factors may have occurred which caused this extra weed growth. Dry conditions prior to any post-emergence herbicide application, weeds too large at the time of application, late or delayed emergence of weeds and lack of thorough coverage of a post-emergence herbicide are some reasons. In addition incorrect rates and lack of required adjuvants may have played a role as well.

Growers should identify weeds now while leaves and flower types may still be present on the weeds to aid in identification. This information along with weed distribution in the fields can help in planning for next year and years following for future weed control programs and correct for any mistakes made during the application (applicator error) as well.

Some species of weeds such as lambsquarters have many different biotypes or versions growing in the same field and thus some are more easily controlled than other lambsquarter types. Giant ragweed and common waterhemp have also recently been found very difficult to control in some area soybean and corn fields this year for glyphosate applications. More research will be conducted in the future on these particular fields and areas within fields but it is important to consider the value of rotation of herbicide sites of action to limit potential weed resistance problems. So the bottom line is to spend some time now to evaluate the success or failure of weed control programs in soybean fields.

(Nathan Winter is an educator — agricultural productions systems with the University of Minnesota Regional Extension Office in Hutchinson.)