What is in this article?:
To lower the risk of developing herbicide-resistant weeds:
1. Identify main target weeds in each field
2. Deploy multiple, effective sites of action (SOA) against target weeds
3. Rotate herbicides with different SOA groups by year
4. Layer residual herbicides, if needed
5. Include SOA groups that have a low risk for developing resistant weeds
6. Control weeds when they are small
7. Don’t let weeds escape to produce seeds
Ryan Britt of Salisbury, Mo., discusses weed issues seen during soybean harvest with his dad, Randy. The farm battles ALS- and glyphosate-resistant waterhemp and marestail, which is especially challenging in a few continuous soybeans fields that limit the ability to rotate herbicide sites of action. With planning, they have created a program with four sites of action: groups 9, 4, 2 and 14.
Preemerge adds sites of action
Your plan should marshal at least two — and preferably three — sites of action for key weeds, says Mark Storr, BASF technical services representative, Nevada, Iowa. The best way to add sites of action: effective, preemergence residual herbicides, he says.
“Effective” is the watchword. You haven’t diversified your chemistry if, say, one of the two sites of action deployed doesn’t control the primary weed in that field, he says. “That’s often lost on people.” Also, “efficacy varies” within the same chemical family, Storr adds. “You need to understand which products control which weeds, so you can pick the right products for your target weeds.”
That starts with proper weed identification, says Young, the Missouri agronomist. In Roundup’s heyday, it wasn’t as important to target specific weeds “because Roundup killed them all.” Go after the most troublesome weed first and get it under control, Bradley says. Do this field by field.
Although a field’s overall weed spectrum usually changes fairly slowly, sometimes a new weed can dominate in short order. “We’re seeing that happen now in Indiana, Ohio and Michigan, where all of a sudden, they’ve got Palmer pigweed,” Bradley says.
So “plans need to be flexible,” Bernard says, “but the cornerstone is a preemergent application before both corn and soybeans.”
Postemergence glyphosate tankmix partners should also be part of your diversification strategy, Bradley says. These treatments “must be planned, they cannot be applied as a rescue. You can’t wait until you see 6-inch waterhemp,” for example, “because you’ve lost the battle by then. It’s all about timing.”