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Research Highlights

Research Highlights
Maryland Farmers can get Ahead of Weeds with Proper Management

Horseweed in a field. Photo: Belmont Acres Farm

By Carol Brown

A plethora of weeds are growing in crop fields across the country and many herbicides designed to kill them are on the market. Finding the right product and the best management practices for the job is crucial before the pesky plants get out of hand.

Maryland extension educator Ben Beale is finding solutions for farmers to overcome herbicide-resistant weeds in their soybean fields. 

 “We’ve been dealing with herbicide-resistant weeds for a long, long time,” Beale said. “Marestail, or horseweed, has been a problem for well over 20 years, and in 2014, we had the first confirmation of Palmer amaranth in southern Maryland.”

This set the weed scientist on the path to finding the best ways to contain the spread of this invasive weed as well as others found in the state. For the last five years, he’s been applying products and combinations of products on weed-infested acres through research projects supported by the Maryland Soybean Board. 

In 2015, he started a study comparing nine products and by 2019 he had expanded to create a treatment protocol with 15 different combinations of pre-and post-herbicide products and a number of cultural techniques for the best combination of products and management tools. 

“This year, 2020, we switched gears and are looking at the new platforms with herbicide tolerant traits,” Beale said. “Our trial is big, with 20 different timing protocols, both early and late. Platforms include the Roundup Ready® system, LibertyLink® and LibertyLink GT27, Enlist® E3, and the Xtend® system.”

Results for farmer success

The research project produced several key findings. Timing is just as important as what product you use, Beale said. A field technician, who is part of Beale’s research team, conducts a weekly survey in the fields and counts the number of emerged Palmer amaranth plants. 

“We have a good understanding of when those plants start to germinate throughout the season and are getting a much better idea of when to apply the post-emergent product,” Beale said. “This is more effective than just waiting four weeks and spraying.”

As for products, the trial displayed good results using the active ingredient flumioxazin found in products like Valor®, and premixes with flumioxazin such as Fierce® and Fierce XLT. Beale also found products with the active ingredient sulfentrazone, found in products such as Authority® or Broadaxe®, to be effective.

“There are a lot of tank mixes on the market with sulfentrazone them and the amount of active ingredient varies,” Beale cautioned. “The key is to get the full rate of active ingredient in the tank mix in order for it to work.”

He also encourages farmers to use a tank mix with multiple effective mechanisms of action, such as Valor and metribuzin, which will provide better, longer-lasting residual than if these products were applied separately by themselves. His research results demonstrated control for two weeks longer and that could make a big difference in the long run.

“A good rule of thumb is to apply a post-emergent about 24 days after planting. To get good control for Palmer amaranth, farmers should use a good residual program and apply the post product when the weeds are less than 3- to 4-inches tall,” he said. “Typically, that will provide good control all season.”

For details on this research, visit the website: https://extension.umd.edu/st-marys-county/agriculture/palmer-amaranth

Other related research: https://www.soybeanresearchdata.com/Project.aspx?id=53959

To find research related to this Research Highlight, please visit the National Soybean Checkoff Research Database.