Four tips for weed seed bank management

MARKLE, Ind. — This is one bank where less is more.

“One question growers have to ask themselves — what is my risk for not having good weed control this year?” said Chad Threewits, Syngenta agronomic service representative for Indiana.

The need for effective weed control is clear each growing season. Weeds compete with corn plants for the vital resources of sunlight, water and nutrients.

But another reason is the long-term impact.

Weeds that reach maturity reproduce millions of seeds that can get deposited in the soil and create headaches for growers in years to come. Some of those seeds can be from weeds that have developed resistance to multiple herbicide modes of action.

Threewits offered four tips for growers to prevent weeds from making a “deposit” into the weed seed bank.

1. Scout Early And Often. Threewits said by scouting fields on a regular basis, growers and service providers can spot weed issues that can pop up unexpectedly, including where weed seed bank “deposits” were made in past years. “In one field, I was scouting for disease, and the field had thin spots in the corn, where it had water laying in the field early on. In those spots, there was a solid patch of waterhemp. That’s the problem. Weeds continue to grow all through the season. That weed seed bank, if that gets built up, we tend to see it longer in the growing season. I was in a field late in the growing season that had new waterhemp coming, that was 2 inches tall and had a seedhead on it,” Threewits said.

2. Size Matters. If you spray a weed taller than 4 inches, it’s more likely to survive the herbicide application and continue growing. This can lead to resistance to that herbicide and/or its active ingredients. Using a herbicide like Acuron® corn herbicide can mean powerful weed control immediately and later on in the growing season. “The products in Acuron, the mesotrione and the bicyclopyrone, can be reactivated by rainfall for long-lasting residual. Let’s say it hasn’t rained since the beginning of the season. If we get a rain, we can reach back and get some of those weeds when they are small. That is a lot of the times when you have weed escapes in corn. Those are the weeds that slip through that very first flush. With Acuron, you get a recharge and reactivation to help take down those weeds that escaped that first application. For example, morning glory can take over a field, just from a few little misses early in the season,” Threewits said.

3. Cover The Bases. Using a two-pass system of Acuron means growers have the reassurance of weed control now and later. “Acuron can be used as a one-pass pre, but we can also do a split application, put half on at pre and half on at post. That really works well to spread that product out so we have multiple sites of action pre- and post-emergence on weeds and especially as we get into heavy pressure and resistant weeds. In case we miss something on the preemergence, we can come in, clean that up and then layer those residuals. That is a strategy we use in soybeans a lot and it also is very effective in corn,” Threewits said.

4. Deal With It. Resistant weeds are getting more numerous, and resistance is increasing. Understanding that and knowing how to deal with it — and fend it off — is key, Threewits said. Changing a farm’s weed management program and not relying on a single herbicide to do all of the heavy lifting needs to be a priority. “We are getting more and more weeds, especially waterhemp and giant ragweed, becoming more resistant to more sites of action in the Midwest. Understanding there is no silver bullet out here, even with the new technology, is important. We have got to put multiple tools and sites of action out there. That’s a big topic and trying to understand what we can do, and knowing the tools we can use to delay resistance on our farms, is key. It’s going to happen and it’s going to happen in our area — but how can we hold that off as long as possible?” Threewits said.

© 2021 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all state or counties. Please check with your local extension service to ensure registration status. Acuron is a Restricted Use Pesticide. Acuron® is a registered trademark of a Syngenta Group Company. All other trademarks are the property of their respective owners.

This column was contributed by Indiana AgriNews for Syngenta.