Kevin Bradley’s phone rang often this summer. Many farmers in Missouri didn’t see the level of control that they expected with postemergence herbicide applications in soybeans. While Bradley could offer possible causes, he couldn’t pinpoint exactly why more weeds escaped than normal.

“We pinned the period where applications seemed to have the most difficulty down to the second and third weeks in June, but we’re still not sure why we didn’t see better control,” says Bradley, state Extension weed scientist at the University of Missouri. “Perhaps it had something to do with dry weather, but we’re not sure.”

Weed specialists often don’t know why an application allows more weed escapes than normal. However, they can offer possibilities.

Why do weeds escape?

If you are seeing weeds pop through the soybean canopy late, Bradley offers four possible causes:

Related:Why 2025 could be a good year for weeds

Focus on weed control

Bill Johnson, Extension weed control specialist at Purdue, adds that cutting herbicide rates may also result in more weed escapes. He’s concerned more growers may leave out residual herbicides and cut rates in 2025.

“That would be a problem with difficult weeds like waterhemp,” Johnson says.

Instead, Johnson suggests cutting some other input. If you want to go after waterhemp and reduce escapes, he acknowledges that it could cost up to $100 per acre. But he believes ineffective weed control, especially if escapes go to seed, is even more expensive.

“Some people talk about ‘foundational’ weed control, referring to cutting rates on residuals,” he says. “To me, that’s not foundational at all. Foundational is applying at full rates. Make them the foundation of your weed control program.”

Here is a program Johnson suggests for waterhemp control: Start with a Group 14 residual herbicide ahead of Enlist soybeans at the full rate. Group 14 choices include Valor, Authority or their premixes. Add metribuzin, active ingredient in Sencor, at full rate.

Come back with a Group 15 herbicide as residual in the post application, such as Dual, Warrant or Zidua at full rate. Make sure the biggest waterhemp plants are no taller than 4 inches, he emphasizes.

“Add in Liberty and Enlist at full rates,” he says. “Some only use one, and I believe that leads to escapes. For waterhemp, you need both.”

If it’s a no-till field, apply residual with burndown if you will plant within two weeks, Johnson advises. “If it’s a month, hold off on residual,” he says. “You want active ingredient there when plants emerge.”