About 65% of soybeans planted in the U.S. this year will possess Enlist herbicide system traits. About 80% of those will be sprayed with an Enlist herbicide containing 2-4,D-choline technology from Corteva Agriscience. Both Tony Goede and Daniel Smydra, Enlist field specialists, emphasize that if you want top performance, you must follow recommendations and use best management practices. No. 1 on that BMP list is spraying weeds while they are small.

“We like to see weeds sprayed at 2 to 3 inches tall, and the official recommendation is 3 inches,” Goede says. “There are several reasons, but for one, smaller weeds don’t shade out weeds just emerging underneath them. That allows for better coverage of those very small weeds.”

The label may list 6 inches as maximum weed height for Enlist, Goede notes. Often, glufosinate, the active ingredient in Liberty, will be added, and maximum weed height for glufosinate is 4 inches. Plus, data from numerous Corteva trials document that your odds of best control are higher when weeds are smaller.

In one trial, Palmer amaranth was sprayed when weeds were 2 to 4, 5 to 6 and 10 to 12 inches tall. Percentage control, respectively, was 93%, 84% and 80%. For common ragweed, numbers were 98%, 96% and 99%.

However, don’t let common ragweed results fool you into thinking the same strategy will work on waterhemp, which might be your toughest weed. Percentage control at bigger sizes of waterhemp dropped, similar to with Palmer amaranth. Waterhemp control at 2 to 4, 5 to 6 and 10 to 12 inches, respectively, was 96%, 89% and 76%.

Related:Understand reduced rate vs. lower labeled rate

Field scenario

OK, so you agree to spray when weeds are no taller than 4 inches. If you have access to your own sprayer and ample labor supply, that might work. If not, here’s the possible rub.

“Say you scout Thursday and determine weeds in a specific soybean field are approaching 4 inches tall,” Goede explains. “You contact your local outlet for custom application. Due to schedules, the weather and other factors, they can’t spray the field until Monday.

“That’s four days. Most data shows that weeds at that stage grow about 1.25 inches per day on average, give or take. By Monday, the 4-inch weed on Thursday could now be 9 or 10 inches tall. You’ve given up 13% or more in weed control potential just on weed height alone, not considering other possible factors.”

Why are weeds tougher to control at 4- to 6-inch heights than if sprayed at 3 to 4 inches tall? And why are 10-inch weeds infinitely harder to control than even the 4- to 6-inch weed? Smydra suggests that part of the explanation lies in understanding simple weed physiology.

Related:Why 2025 could be a good year for weeds

“Weeds add growing points along the stem quickly during early stages of growth,” he explains. “If there are more growing points, that means there is more surface area to cover with active ingredient.”

Work by plant physiologists indicates that on a typical 2-inch-tall waterhemp plant, you will likely find nine growing points. By the 3- to 4-inch height, there will be around 14 growing points, and at 4 to 6 inches tall, expect an average of 18 growing points.

“On a 10-inch plant, there are literally almost too many growing points to count,” Smydra says. “Plan to spray as early as possible when weeds are smaller, with fewer growing points.”