Do You Need a Burndown Herbicide?

Published on: 15:51PM Feb 02, 2016

As you prepare for pre-season weed control, you'll want to consider burndown and  pre-emergent herbicide options.

How do you decide? It depends. In some cases, you may need to use both, but in other fields, a single application of pre-emergent will suffice, without burndown. 

Here's what you need to know. 

First, you need to understand when to use burndown herbicides versus using pre-emergent herbicides. According to Curtis Thompson, Kansas State University professor and Extension weed science specialist, burndown should be used to control weeds that have already emerged and pre-emerge should have residual control to stop new weeds from coming out of the ground.

“If you use no-till, you’ll likely need something to destroy weeds,” Thompson says. “That’s the burndown program.”

To discover if you’ll need to use burndown herbicides this spring, ask yourself two simple questions:

1. Do you have weeds in your field now? If your answer is yes, , then you might need to consider a burndown herbicide. Since these weeds are already ahead of your crop, they will steal sunlight, nutrients and water from the young plant. Don’t neglect to take your tillage practices into account before spraying. If your answer is no, you might be OK to skip the burndown. But be sure to monitor your fields for any possible growth. You might still need to use pre-emergent to keep fields clean at the start of the season.

2. Will you till your soil before planting? If your answer is yes, you likely won't need to use burndown herbicide since tillage rotates the soil and pushes the weeds under. If your answer is no, plan for a burndown to gain control of weeds.

If burndown is needed, February is the time to get in the fields and make this happen. “Don’t be penny-wise and pound-foolish,” says Mike Owen, Iowa State Extension weed scientist. “It’s false economy to try to save money by reducing herbicide rates. Buck up and use the correct rates.”

Don't forget to evaluate which herbicides will be effective for your fields. Some common pre-season weeds such as marestail have resistances to multiple herbicide groups. Study herbicide resistance charts to make sure you're applying a product that will work for on your farm's weeds.

What makes this so important? Early-season corn and soybeans need to focus all of their energy on growing. Don’t get your crops off to a bad start by planting into a field where weeds have a head start.