Pre-Emerge Herbicides Need Post-Emerge Clean-up

Agronomy
waterhemp in soybeans

There are fundamental principles for managing weeds in soybeans that apply to all tillage systems and trait platforms, including conventional systems. Kevin Carlson, Federated’s agronomy manager, said, “One of the most important principles is to start with a good pre-emerge program that has residual control of problematic, resistant weeds.”

Whether it’s no-till, minimum till, or conventional tillage (though in no-till we also add burn down), Roundup Ready®, Liberty®, Xtend®, Enlist®, or conventional crops, “they all start with a good pre-emerge herbicide program designed around today’s problem weeds,” he said, reiterating: “No matter the system, they all start the same, with a good pre-emerge herbicide.”

The similarities don’t stop there. Every tillage or crop system (including soybeans) needs a similar, planned – second pass – post-emerge program.

“We need to spray small weeds, controlling them early,” he said. But how?

“Mark your calendar,” Carlson said, “and then, 20-30 days after the planting and pre-emerge herbicide application, it's time to scout and do post applications. Don't wait.”

The early weeds are the ones that most adversely affect yield. The early weeds also produce more seeds at the end of the year (if they get that far). Weeds that come late, past mid-July, don’t compete with the crop as much and produce less seed.

Thus, when managing corn and soybeans in the same season, there is a 20- to 30-day window to complete the corn herbicide applications “so we can get to the soybeans in a timely manner,” said Carlson. Here’s the priority for herbicide applications, as Carlson described:

  1. Start with planned pre-emerge applications to soybeans.
  2. Move to corn herbicide applications, and finish as much as possible, but pay close attention to the 20- to 30-day window.
  3. Don’t wait . . . get back to the soybeans and do the necessary post-emerge spraying.

Remember, said Carlson, with great emphasis: “Post-emerge applications are just a cleanup of the pre-emerge application.”

Talk to your Federated Agronomist to get your pre- and post-emerge herbicide plans in place.