pray small weeds. Use residual. Get good coverage. We’re all familiar with these best practices for post-emergence soybean herbicides. They are standards for good reason. Consider studies cited by the University of Nebraska-Lincoln’s CropWatch showing that if weeds grow to 9 inches, soybean yields can be reduced as much as 6%; 12-inch weeds can slice 10% off yields.
This year’s supply and price challenges up the ante. Farmers need to get things right the first time and be more strategic with their applications, says Leslie Lloyd, an AgriGold agronomist in the Southeast. For instance, he recommends farmers use a mix of pre-emergence herbicide products that require a lot of water for activation and some that require very little so producers are covered regardless of the amount of rain they get for activation.
Just how much rainfall is required to activate residual herbicide depends on many factors, including its water solubility, weed sensitivity to the active ingredient, weed development at application and more. Purdue University Extensions Entomology provides more details on how this varies by active ingredient.
Limited supply and high prices prompt more precision
If a pre-emergent product with two or three modes of action was not available at planting, know that many residual products can be added to your post-emergence spray, Lloyd says. Some farmers use both a residual pre-plant and add a residual in their post-emergence spray, he notes.
Glyphosate availability is another concern. Lloyd says growers are debating how best to use the glyphosate they have on hand. “It’s not just the availability of product. The cost of it has become more of a consideration,” he says. “Three years ago, you didn’t care what glyphosate cost, you just put it on. Now you care a lot because the price has surged.”
“That situation is going to drive more precision and timelier applications,” Lloyd predicts.
Scouting will be key
Scouting for weeds is even more critical with these high-cost applications. Lloyd explains, “If you don’t need a certain product because you don’t have those species of weeds, that saves money.”
The rule of thumb is to scout fields 14 to 21 days after they’ve been planted. “Post-emergence spraying generally occurs three weeks after planting, so that’s a good timeframe to identify which weed species are present,” he explains.
No room for error
When you apply your post-emergence herbicide, you need to make sure you’re getting things right. This year’s prices and supply crunches mean do-overs are not an option.
A common mistake Lloyd observes in his area is not using enough water with glufosinate herbicides. “More water. More coverage. More is always better with glufosinate,” he says.
In many cases (not just with glufosinate), using enough water can help farmers avoid costly resprays. “They need to do an excellent job the first time, and that usually means 15 to 20 gallons of water [to provide coverage],” he details, reminding that it’s imperative to follow labels.
Be strategic with herbicide choices for double-crop beans
Double-crop soybeans that are common in some areas of the Southeast present an additional challenge: It’s tough to adhere to dicamba labeling restrictions given their production period. For that reason, Lloyd says many farmers spray their dicamba early and save their Liberty herbicide for later in the season.
“If supplies of glufosinate products are limited, they may need to be saved for your double-crop soybean needs,” Lloyd says. He advises reviewing all federal and state labels regarding herbicide applications timing and cut-off when making decisions about applications in your area.
Growers in his area are also on edge about the future of dicamba, given recent court decisions and uncertain, and sometimes contradictory, messaging from the EPA. The situation drives home AgriGold’s advantage in offering farmers several platforms from which to choose.