Follow-up to Postemergence Weed Control in Soybeans

Published on 23 Aug 2017, 08:00 AM • by: Dawn Kielsmeier, Northwest CCA Soy Envoy • 1116 Views

Weeds are tough to control today, but throw in weather-related issues and it’s a recipe for disaster.

This season we are facing some tough weed challenges in Illinois. In my blog last month I reviewed the weed control struggles I have been seeing this season. I have since had the opportunity to evaluate herbicide applications on some of this season’s more difficult weeds, and here is what I have found.

Marestail – In my experience, the best control of this weed was made with an application of Classic® and Resource® together. That application seems to have killed most of the marestail in this field.   


A FirstRate® and 2,4-DB application did a decent job of holding the marestail back and stunting it, but didn’t kill it. We will see what this looks like later in the fall.


There were some growers that used a rope wick applicator with straight 2,4-D in it to kill off the marestail and this did a decent job, if marestail was above the canopy. This is really going back a few years when we used to rope wick for hemp dogbane and wirestem muhly control. 

Waterhemp: This weed is a particularly vexing problem for farmers. We had good luck with waterhemp using the LibertyLink® system and will continue with that for next year. The key to waterhemp is to go after it early when it’s small, continue to monitor it for each flush and respray if necessary. We all like to see clean fields with no waterhemp coming through.



Giant ragweed: Giant ragweed is becoming a bigger problem every year. Some growers sprayed four times to clean up giant ragweed that is extremely tolerant of Roundup®. In the future this weed will need to be handled with more residual products. 


In conclusion, we need to learn to manage these weeds hard to handle individually, so that we get the right timing, products and rates to control them.  The time of one size fits all (think back to Roundup and Roundup Ready® 20 years ago) is now past.

Dawn Kielsmeier is an agronomy sales specialist with Pearl City Elevator in Baileyville, Ill. She has a B.S. in dairy science and an M.S. in agronomy, both from the University of Illinois and has been a CCA since 1993. She is a 2017 Illinois Soybean Association CCA Soy Envoy.



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