Soybean School: Taking advantage of fall weed control


Combines are rolling and as soybeans move to the bin, agronomists are reminding growers that the potential for an open fall presents a great opportunity for weed control.

BASF agronomist Ken Currah says fall is the perfect time to tackle tough weeds like dandelion, Canada thistle and perennial sow thistle. “This is the time to get those weeds and really lay a nice foundation for a comprehensive weed control program.”

On this episode of the RealAgriculture Soybean School, Currah looks at strategies to control weeds in cereal stubble and how cover crops impact this situation; he also discusses opportunities to target weeds in soybeans after the combine leaves the field.

In soybean stubble, dandelion, members of the thistle family, and weeds like wild carrot can be targeted with contact herbicides. In the video, Currah discusses rates and management tips for systemic Group 9 (glyphosate) and Group 4 (dicamba and 2,4-D) herbicides, which translocate active ingredients to the roots of plants.

“That’s the name of the game this time of year. Sending herbicide along for the ride as the plant is driving photosynthates down to its crown and root system to overwinter and start up again next spring,” says Currah. He adds that Ontario Ministry of Agriculture, Food and Rural Affairs weed specialist Mike Cowbrough has provided excellent rate recommendations on what it takes for contact herbicides to take out dandelion and other tough-to-control weeds. (Story continues after the video.)

Currah also points out that the weed control window stretches well into the fall. “Usually the first frost has been our cue to winterize the sprayer,” but he notes that Cowbrough’s research indicates control of a weed like perennial sow thistle can be increased by as much as 20 percent when sprayed after it’s been nipped by the first frost.

It is important to remember that herbicide response is slower in the fall compared to the speed of activity observed with spring applications. That’s key for growers who want to do fall tillage, says Currah. They need to wait for at least two weeks after spraying to ensure herbicides have translocated to the roots and impacted the weed.

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