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Lack of Federal and State Labels May Limit Use of Dicamba-Tolerant Soybeans in 2016

Thinking about planting Roundup Ready 2 Xtend Soybeans that resist dicamba and glyphosate? After all, Monsanto earlier this month announced a full commercial launch of these soybeans for 2016 following China’s decision to accept import of these varieties. 

That said, you may not be able to fully use the technology this year. No federal or state labels for any preemergence or postemergence applications of any dicamba-containing product has yet been granted, says Aaron Hager, University of Illinois Extension weed specialist. It’s uncertain whether these labels will be granted in time to allow application of dicamba-containing products on these varieties early or even later into the 2016 growing season. With no label approval, applying a dicamba-containing product to these soybean varieties violates both state and federal laws, says Hager. 

So can dicamba be applied prior to planting dicamba-resistant soybean varieties? 

Yes, but remember that this type of application must follow the herbicide label guidelines regardless of the soybean variety planted, says Hager.  

For example, following a Clarity (containing dicamba) application preplant to existing vegetation – including dicamba-tolerant soybean varieties – with 1 inch of accumulated precipitation, a waiting interval of 14 days before planting is required for up to 8 ounces of Clarity. For 16 ounces of Clarity, the waiting interval is 28 days. This use pattern is governed by the herbicide label, not by the soybean variety planted, says Hager. 

Uncertainty exists with other new herbicide-tolerant systems, too. The Enlist Weed Control System that includes Enlist Duo herbicide has received regulatory clearances, but China has not given its approval for import of these soybeans. It’s unclear how widely available these varieties will be in 2016, says Hager. 

Herbicide-resistant weeds still plague farmers 
New herbicide-tolerant systems would be useful for farmers, as herbicide-resistant weeds plague many farmers. 

In Illinois, waterhemp and horseweed (marestail) are the two most common herbicide-resistant weed species in Illinois, says Hager. Observations during 2015 suggest these species are likely to remain prevalent in 2016, he adds. More than 1,300 waterhemp samples (representing 236 fields) were submitted to the University of Illinois Plant Clinic in 2015 for herbicide resistance screening. The sheer number of samples submitted suggests that herbicide-resistant waterhemp continues to significantly challenge farmers, says Hager. 

Waterhemp plants or populations that resist herbicides from more than one site-of-action group are increasingly common, he adds. That’s not likely to change. Recent Illinois survey data indicates resistance occurred in close to 90% of the fields sampled, and multiple resistance to glyphosate and PPO inhibitors was confirmed in 54% of the fields sampled.

If you’re planning on relying on a dicamba-tolerant system in soybeans to control waterhemp that resists both glyphosate and PPO inhibitors, consider using alternative strategies, says Hager. Strategies for managing weeds that resist multiple herbicide sites of action include:

• Rotating fields to a different crop.

• Planting soybean varieties that resist glufosinate (Liberty) and using glufosinate as a postemergence herbicide.

Use an integrated approach 
Regardless of the crop planted, the variety selected, or the herbicide applied, the most sustainable way to manage herbicide-resistant weeds is an integrated weed management system, says Hager. This uses both chemical and nonchemical tactics to eliminate weed seed production throughout the growing season, says Hager. 


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