Farm Progress

Ask a CCA: Giant ragweed has become the number one weed problem in several counties.

January 23, 2018

3 Min Read
soybean field

By Harold Watters and Jeff Stachler

Ohio State University Extension educators from around the state have evaluated weed control in soybean fields every fall since 2006. This past fall, 25 Extension educators viewed over 2,000 soybean fields and 130,000 acres.

The results of the data showed 28% of soybean fields in the state were weed-free. This is great, but means that the majority of fields still had weeds at harvest time, so there is some work that needs to be done.

What are the most prevalent weeds in soybeans?
Marestail, giant ragweed and volunteer corn are still the most common weeds being observed in soybean fields. Giant ragweed is spreading fast, and has become the number one weed problem in several counties. This spread is likely due to an increase in frequency and level of resistance to glyphosate, and to Flexstar becoming less effective. The other weed of concern is waterhemp, a pigweed species. It is showing up in more regions of the state and increasing rapidly in some areas.  Waterhemp is most prevalent in West Central Ohio where waterhemp has increased from 21% in 2015 to now 47% in Auglaize County as an example. This weed will drastically change weed management, and cause a substantial increase in herbicide costs.

What methods are available for weed control?
We have tools available beyond Roundup Ready herbicide technology to manage these problematic weeds that are resistant to glyphosate. One such tool is LibertyLink. A change within the last year allows LibertyLink to be applied at a total seasonal amount of 87 fluid ounces per acre. This increased rate more effectively controls some of the tougher weeds. To maximize control of weeds in LibertyLink corn and soybean, a comprehensive burndown or tillage along with strong residual herbicides is necessary.

Another tool available for a second year is Xtend soybeans. Dicamba very effectively controls marestail and giant ragweed in the burndown and postemergence. Dicamba is fairly effective on waterhemp, but some 2018 research showed not all plants were controlled, but that occurred with Flexstar as well.

What label changes have occurred?
There are several label changes for XtendiMAX, FeXapan and Engenia. A big change is that these products are now restricted use, so you must have an applicator’s license to apply them. Applicators must attend a two-hour training session on how to properly apply these newly restricted products. In Ohio, these classes will be delivered by the herbicide manufacturers. Visit to find links to register for these meetings.

Other label changes are as follows:

• The products can only be applied in 3 to 10 miles per hour wind speeds as long as there are no downwind sensitive crops.

• Specific records must be taken according to the label within 14 days of the application and kept for two years.

• Applications can only be made from sunrise to sunset.

• Stronger language has been added concerning spray tank cleanout.

• Additional language about sensitive crops has been added.

Is Enlist corn available?
Enlist corn is now available for 2018.  It is resistant to 2,4-D, glyphosate, glufosinate, and the “fop” herbicides. The Enlist soybeans still have not received full export clearance, so full use of Enlist soybeans in 2018 will not be available. There will be areas in the country where Enlist soybeans will be planted, but strict guidelines must be followed to keep the soybeans out of export channels.

Soybeans resistant to Balance are fully approved for export, so they can be grown. However, there are no products legally available to be applied at this time, so they are not actively being sold.

Watters and Stachler are Ohio State University Extension educators and can be contacted at [email protected] and [email protected], respectively.

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