Research HighlightsHow Foliar Nutrients Interact with Weed Control
Highlights:
- In soybeans, foliar nutrients can be added to post-emergence herbicide applications to weed and feed at the same time.
- In a Delaware trial, adding foliar nutrients didn’t impact herbicide injury.
- Herbicide applications with foliar nutrients provide comparable weed control under optimum conditions, but with less-than-ideal herbicide applications, nutrients could unintentionally benefit weeds along with the soybean crop.
By Laura Temple
Farmers aim to get the most out of every trip across their fields. When spraying, they include multiple inputs in the same tank whenever it makes sense.
“Adding micronutrients to post-emergence soybean herbicide applications is often done in this region,” says Mark VanGessel, weed science professor and extension specialist at the University of Delaware. “Over a conversation at lunch, a farmer said he thought he got better weed control when including them. He asked if data supported that.”
VanGessel did not have any evidence related to this observation. However, the Delaware Soybean Board agreed to fund Soy Checkoff research to learn how foliar nutrients might impact herbicide injury and weed control. He designed a one-year trial to gather data for both herbicide-tolerant and conventional soybeans.
Combining Foliar Fertilizer and Herbicides
Given the volume of foliar fertilizer options on the market, VanGessel started by reviewing product sales literature, looking for claims related to weed control. He selected three products with those claims representing different categories within foliar fertilizers.
- Multiple micronutrients
- Macronutrients and micronutrients
- Primarily macronutrients
In addition, he included sucrose, sometimes touted as another way to feed a soybean crop.
VanGessel and his team added those products to standard post-emergence herbicide programs applied at the V3 vegetative growth stage, in plots with Palmer amaranth as the primary weed pressure. They used a three-way mix of glyphosate (Roundup), 2,4-D (Enlist) and glufosinate (Liberty) in the herbicide-tolerant soybeans. They sprayed conventional soybeans with a mix of fomesafen (Reflex), bentazon (Basagran) and clethodim (Select Max).
Then, they evaluated crop safety indicators like leaf burn, discoloration and stunting, as well as weed control.
“From a crop safety standpoint, nothing jumped out,” he reports. “We observed leaf burning and stunting on conventional soybeans from Reflex and Basagran, but only slight differences between the nutrient treatments. However, we didn’t see any clear soybean health responses from foliar nutrient or sucrose applications. As expected, we did not see any leaf burn or stunting from the treatments to the herbicide-tolerant soybeans. But, there was no enhanced growth as a result of using any of the nutrient additives.”
Controlling Versus Helping Weeds
VanGessel says weed control was comparable across all treatments, with one exception.
“When adding the product with multiple micronutrients to the Liberty, Enlist One plus glyphosate application, fall panicum control was lower by about 10% compared to no additives,” he explains.
He saw similar trends in companion trials snap beans. The nutrient treatments did not improve crop response to the herbicide treatments.
“As far as weed control, with good herbicide programs applied at the right time, the nutrients did not affect weed control,” VanGessel says. “When weed control was less than ideal, the added nutrients allowed the weeds to recover.”
He describes scenarios leading to less than ideal weed control, where foliar nutrients may benefit weeds by supporting recovery from incomplete herbicide control.
- When herbicides are applied to weeds taller than 4 inches, the weeds are more likely to survive.
- Applying reduced herbicide rates may not provide complete kill, and nutrients in the tank may aid recovery from herbicide damage.
- Using the wrong sprayer tips for specific herbicide applications often results in poor weed coverage. Again, foliar nutrients intended to feed soybeans could also feed weeds so they overcome the herbicide.
“Weed recovery was more obvious in the snap bean trials,” VanGessel notes. “That was probably due to labeled rates for those herbicides are lower in snap beans than in soybeans.”
However, he says the principles in the snap bean trials translate to soybeans.
“With foliar fertilizer and herbicides, farmers and applicators need to do the little things to maximize weed control effectiveness, like applying at the right timing and using the correct nozzles,” he says. “Allowing weeds to recover from partial control could be an unintended consequence of tankmixing with foliar fertilizers.”
However, when following best weed control practices, adding nutrients to a soybean herbicide application can help farmers get the most from that trip across the field.
Additional Resources
Weed Management – SRIN information page
Palmer amaranth – GROW information page
Determining the Impact of Foliar Nutrient Feeding on Soybean Yield – SRIN article
Foliar Fertilizers Rarely Increase Soybean Yield – SRIN article
Foliar Fertilizers in Soybean Production – Science for Success YouTube video
Meet the Researcher: Mark VanGessel SRIN profile | University profile
The Soybean Research & Information Network (SRIN) is funded by the Soy Checkoff and the North Central Soybean Research Program. For more information about soybean research, visit the National Soybean Checkoff Research Database.
Published: Jun 8, 2026
