With new dicamba soybean herbicide technology expected to come to market in 2017, growers will need to be mindful of preserving the technology while at the same time tailoring a weed management program that keeps fields clean.

First and foremost, growers should temper their expectations regarding the dicamba technology, said Aaron Hager, Extension weed specialist at the University of Illinois, noting all weed management strategies that growers have been employing still apply.

Aaron Hager, Unviersity of Illinois Extension weed specialist

"This isn’t taking us back to the good old days when we could spray virtually any size weed with Roundup, and they’d die," said Hager. "If you’re late spraying or your rate is inappropriate for the stage of weed growth, not only will the application be less effective, but you’ll also be promoting the development of dicamba resistance."

Driver weeds should be the focus of each field’s weed management program. Knowledge is power – know the field’s weed pressure history and know everything you can about your driver weeds.

"The driver weed across most of Illinois is waterhemp," said Hager. "Twenty-five years ago, you couldn’t find two people in Illinois who knew what waterhemp was. Have farmers learned about it now? They sure have. Biology has forced them to learn about driver weeds to understand how to control them."

Furthermore, he said multiple modes of action are still necessary to target your weed spectrum and limit resistance.

"If you’re using dicamba because glyphosate is no longer effective against your driver species, you’re exposing the weed population to only one effective herbicide, and that’s a recipe for the evolution of resistance," he said.

Hager also reminds growers to be mindful of dicamba’s off-target movement. Dicamba use in soybeans means growers will be spraying later in the season when temperatures are warmer and humidity levels could be higher.

The concern is drift could impact non-target crops and/or vegetation of homeowners, orchards or vineyards. Follow label instructions for application, paying careful attention to use approved nozzles, apply during the right wind speed and know bordering crops.

Waterhemp

Preserving Weed Management Tools
While Syngenta and others are actively engaged in discovering new soybean herbicides, no companies are expected to introduce a new herbicide mode of action in the foreseeable future, making it vital for growers to preserve weed management tools and technologies, like dicamba.

Dane Bowers, Syngenta herbicide technical product lead, recommends the following weed management practices:

  • Start clean: Know what weeds are present in the spring, then apply an effective burndown herbicide to set up a clean field for planting.
  • Don’t wait: Make timely, full-rate applications before weeds are 3 to 4 inches tall.
  • Importance of residual: Offer multiple effective modes of action on the target weed and provide residual activity.
  • Season-long monitoring: A second post-emergence application may be required.

Reduced rates may reduce costs short term, but they create long-term problems. Sub-lethal herbicide doses increase weed selection pressure, so weeds emerge that could cross pollinate and allow more resistant genes to spread in the weed population.

Dane Bowers, Syngenta herbicide technical product lead

"Try to prevent weeds from going to seed. Escaped weeds may be most tolerant or resistant to herbicide treatment and will produce seed which can emerge the next time the same herbicide is applied," said Bowers. "This adds weed seed into the seed bank and can quickly shift the population from susceptible to resistant weeds. It’s a numbers game – the more weeds sprayed, the more likely the grower is to find that one in a million that may be resistant."