Resistant weeds are an increasing problem across the Midwest. Some broadleaf weeds, including waterhemp and Palmer amaranth, are developing resistance to PPO herbicides in soybean fields, leading to weedy corn and soybean fields. Weedy soybean fields in 2015 can carry over and lead to weedy cornfields in 2016, depending on crop rotation. There’s little doubt current weed control programs are losing effectiveness, and new chemistries are needed for optimal weed control.

EFFECTIVE WEED CONTROL: Using a preemergent herbicide that incorporates multiple active ingredients and effective modes of action that work well across different environments and soil types is the best approach to weed management when applied at a full rate.

Preemergent herbicides have become a mainstay in weed control programs as they control weeds from the start, limiting the ability of weeds to rob corn plants of nutrients and water. With weed resistance expanding, optimal weed control is only achieved when a powerful herbicide, with multiple modes of action and active ingredients, is used at a full rate.

“Glyphosate-resistant waterhemp is among the most difficult weeds to control in Iowa,” says Dean Grossnickle, agronomic service representative at Syngenta. “Weeds are becoming resistant to different herbicides, and attacking weeds with just glyphosate is becoming less effective.”

Best bet is to control weeds before they emerge
All hope isn’t lost when it comes to defeating tough weeds. Using a robust preemergent herbicide that incorporates multiple active ingredients and effective modes of action that work well across different environments and soil types is the best approach to weed management when applied at a full rate.

“If weeds are resistant to one active ingredient in a herbicide, the effectiveness of that herbicide is reduced since all of the weed control must be provided by the other active ingredients in the premix,” says Gordon Vail, Syngenta’s technical product lead. “It’s important that growers use full labeled rates to defeat tough weeds that are resistant to different herbicides.”

The effectiveness of a soil-applied herbicide is determined by its ability to withstand all biological, physical, chemical and environmental factors working against it. To manage these factors that influence herbicide performance and weed control, a dependable herbicide must have effective active ingredients that work well under different environmental and soil conditions. The active ingredients in Acuron corn herbicide from Syngenta provide different physical and chemical properties to help growers effectively control weeds across many environments and soil types, says Vail.

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“Properties including soil adsorption, degradation and water solubility are all key components that determine a herbicide’s effectiveness,” he adds. “It’s unlikely growers will have perfect conditions season-long, so a herbicide that’s able to work effectively across different conditions is the key to a successful season. Other herbicides often have active ingredients that work best in ideal weather conditions or in areas with adequate soil water.”

Numerous benefits of using a full labeled rate
A herbicide with multiple modes of action applied at effective rates is critical to sustainable weed control. A full application rate of a herbicide allows for longer residual control versus what would be achieved with a reduced rate.

“Strong active ingredients can only work in tandem to deliver powerful weed control if the proper amount per acre is used; otherwise growers risk the possibility that tough weeds will emerge,” says Vail. “Longer residual control is achieved when active ingredients have physical properties that lead to powerful, season-long control and crop safety.”

Fred Steck, a grower from Carman, Ill., says after using Acuron at a full-rate, preplant, he saw weed control unlike what he had seen in previous years. “Cocklebur and morningglory never curled up much in the past, but Acuron seemed to nail them both,” he says. “We use irrigation, and it can be tough to find herbicides that last, but I’m pleased with the residual control offered by Acuron.”

What’s the future in weed management?
Intense weed pressure will likely increase over the next few years, which will influence growers’ herbicide program decisions. “Certain broadleaf weeds grow aggressively, and combined with adequate rain, they’ll germinate throughout the growing season,” says Grossnickle. “Robust preemergent herbicides used at a full rate will keep growers’ fields clean.”

Another effective solution containing multiple active ingredients and added flexibility is Acuron Flexi corn herbicide, a product that received EPA registration in February 2016. Farmers in certain areas of the Corn Belt, including Iowa, Minnesota and Wisconsin, will find this product especially useful, since they are limited on using atrazine for various reasons.