Spray 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.
Recent 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.
Cover your bases
Of course, farmers need to follow the mantra of using overlapping residuals and multiple modes of action when it comes to herbicides. “I think farmers are doing that when they can,” Lloyd observes.
If possible, Lloyd also says farmers should use a mix of post-emergence herbicide products – some that require a lot of water for activation and some that require very little – so they’re covered regardless of the rain situation.
Just how much rainfall is required to activate residual herbicide? That depends on its water solubility, weed sensitivity to the active ingredient, weed development at application and other factors. Purdue University Extensions Entomology provides more details on how this varies by active ingredient.
If a pre-emergent product with two or three modes of action isn’t available at planting, Lloyd says that many residual products can be added to your post-emergence spray.
Some farmers use both a residual pre-plant and add a residual in their post-emergence spray. He believes layering pre-emergence products even as farmers make their post-emergence applications is “just a smart thing to do.”
Get creative to stretch post-emergence herbicides
Lloyd saying growers are debating how best to use the glyphosate and glufosinate they have on hand.
“It’s not just the availability of product. The cost of it has become more of a consideration,” he explains. “Three years ago, you didn’t care what glyphosate cost, you just put it on. Now you care a lot because the price has nearly tripled.”
Lloyd expects this to drive more precision and timelier applications and urges producers not to just automatically put glyphosate in their tank mix for corn herbicides.
He believes the name of the game will be utilizing everything in the toolbox, so you don’t get caught without a needed product. “Unfortunately, we’ve relied on just two main tools for way too long,” he says.
Farmers should look at what they have and what their retailer can obtain for herbicides and think through how they can stretch their total product mix. They may need to get creative and consider dusting off old tools like Steadfast® Q (formerly Steadfast) for field corn or seek alternatives like Reviton™ (a new non-residual, non-selective burndown from Helm Crop Solutions) for certain applications.
Scouting will be key
Scouting for weeds is even more critical with these high-cost applications. “If you don’t need a certain product because you don’t have those species, that saves money,” Lloyd says.
The rule of thumb is to scout fields 14 to 21 days after they’ve been planted since post-emergence spraying generally occurs three weeks after planting.
Besides identifying weed species, Lloyd says farmers also need to pay attention to weed size to ensure good coverage with post-emergence products.
No room for error
When you apply your post-emergence herbicide, make sure you’re getting things right. Recent 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 like Liberty®. “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.
“I’ve found you can spray it twice with 15 gallons each for a total of 30 gallons or you can do it once with 25 gallons. It just does a better job and is more economical if you don’t have to go back that second time,” he says. “Pump your water up. Use the proper amount of ammonium sulfate products. Follow labels. Do all those things that are going to allow you to get the job done right the first time. We can’t cut corners.”
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. Therefore, Lloyd says many farmers will 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 needs,” Lloyd says. He advises reviewing all federal and state labels regarding herbicide application timing and cut-offs when making decisions about applications.
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 Environmental Protection Agency.
The situation drives home AgriGold’s advantage in offering farmers several platforms from which to choose. Reach out to your local AgriGold agronomist for more advice for navigating this season’s unique input challenges.