ANKENY, Iowa (DTN) -- Lessons learned managing volunteer corn after the 2020 Midwest derecho can help farmers in 2022 and beyond.
Farmers did a respectable job managing volunteer corn after the windstorm on Aug. 10, 2020, damaged or flattened millions of acres of corn, according to Meaghan Anderson, Iowa State University Extension field agronomist based in central Iowa.
Anderson's territory sustained some of the worst damage from the derecho. Winds hit 140 miles per hour, which forced some farmers to destroy cornfields that couldn't be harvested or lose countless ears and kernels in lodged fields. It heightened concerns about volunteer corn in 2021.
For the most part, Anderson said growers effectively used herbicides, tillage or a combination of the two to keep unwanted corn from significantly reducing 2021 yields. But that's certainly not the case across the board. After talking to farmers this summer with soybean fields filled with volunteer corn, Anderson has a pretty good idea of what went wrong.
"The majority of people who did a good job took to heart the antagonism issue with soybean herbicides," Anderson said. Those that didn't worry if the grass herbicide they chose to kill volunteer corn would play nice with a herbicide to control broadleaf weeds likely had volunteer corn problems, she continued.
"The biggest lesson learned ... antagonism was a serious issue," Anderson said. Herbicide antagonism is when the result of two or more chemicals combined is less than the predicted effect of each herbicide applied separately.
It wasn't a derecho, but a string of severe thunderstorms in the upper Midwest in late August 2021 that caused extensive corn lodging. Though no official government acreage estimates are available, damage is likely in the tens of thousands of acres -- the most severe cases in northeast Iowa. Read a DTN story about the storms here: www.dtnpf.com/agriculture/web/ag/crops/article/2021/08/31/violent-august-storms-pound-midwest.
Anderson anticipates volunteer corn issues in 2022 on farms affected by the latest storms. She said lessons learned from the derecho can mitigate future problems.
"I cannot emphasize enough the antagonism issues with herbicides," Anderson said. "I thought we (Extension) did a real good job talking about it last winter, but with the number of phone calls we still get, it's quite clear it's an issue we need to continue to keep broadcasting."
ISU Extension recently provided several tips -- https://crops.extension.iastate.edu/… -- to better manage volunteer corn.
AVOID HERBICIDE ANTAGONISM AND FOLLOW LABEL INSTRUCTIONS
Tank mix partners such as 2,4-D and dicamba can have a dramatic reduction on efficacy of Group 1 grass herbicides due to herbicide antagonism. However, that can be avoided.
Antagonism generally can be reduced by applying a higher rate of the grass herbicide in the tank mix or avoided by applying the grass herbicide one or more days before or seven days after the broadleaf herbicide. At times, an additional postemergence pass of only a Group 1 product may be needed.
WinField United Agronomist Tyler Steinkamp agreed that herbicide antagonism played a big role in volunteer corn problems this year. So did not following herbicide labels, such as not adding an adjuvant when needed.
At the WinField United Answer Plot near Jesup, Iowa, the company's volunteer corn demonstration showed what success and failure looks like. Section Three (a Group 1 herbicide) applications were made on volunteer corn with and without an adjuvant at different herbicide rates. Volunteer corn that was sprayed following the label and using an adjuvant died. Corn that was sprayed without an adjuvant -- at label rates and not at label rates -- survived.
"When you read many herbicide labels, some will ask for adjuvants," Steinkamp said. "Some farmers don't remember to add them. Demonstrations like this show the importance of following the label."
GROUP 1 GRASS HERBICIDES (ACCase INHIBITORS)
Here's a list of Group 1 herbicides and application rates per acre provided by ISU Extension to control volunteer corn in soybeans:
-- Select Max 0.97EC, 6-12 fluid ounces.
-- Clethodim 2EC, 4-6 fluid ounces.
-- Assure II/Targa 0.88EC, 4-8 fluid ounces.
-- Fusilade DX 2EC, 4-6 fluid ounces.
-- Poast, 12 fluid ounces.
WinField United claims Section Three herbicide, which is clethodim, is effective against volunteer corn at various heights at suggested rates: up to 12-inch-tall corn, 2.7-4 fluid ounces per acre; up to 24-inch corn, 4-5.3 fluid ounces per acre; and up to 36-inch corn, 5.3-6.7 fluid ounces per acre. However, the herbicide needs an adjuvant such as Destiny HC or Superb HC to be the most effective.
Brock Hansen of Baxter, Iowa, anticipated major issues with volunteer corn this year after the 2020 derecho caused extensive corn lodging and ear droppage in his fields.
As the 2021 soybean harvest gets underway, Hansen said management strategies to keep unwanted corn at bay worked well.
"It's not bad," Hansen said, referring to volunteer corn in fields. "You can feel it go through the combine, but it's not hurting anything. It's just robbing a little power."
Here's Hansen's strategy:
-- Despite being a no-till operation, a vertical tillage tool was used on most acres with lodged corn to size residue. However, seed incorporation was minimal to reduce the chance of germination in the spring and increase the odds of being eaten by wildlife.
-- More soybeans were planted and less continuous corn.
-- A full rate of pre-emergence Sonic herbicide was used before planting.
-- One or two postemergence applications of Fusilade herbicide were applied to control volunteer corn.
"There are some eyesores here and there, but the volunteer corn was manageable," Hansen said.
OTHER ISU EXTENSION TIPS TO CONTROL VOLUNTEER CORN
-- Rotate wind-damaged cornfields to soybeans to provide for more herbicide-management options.
-- Not rotating to soybeans and sticking with corn is feasible where herbicide options, such as glyphosate and glufosinate, are available to kill volunteer corn plants.
-- Tillage can be an effective option to control volunteer corn, but it can also increase seed-to-soil contact that can promote germination.
-- Graze or bale corn stalks in wind-damage fields with significant lodging.
-- A non-selective herbicide, such as Gramaxone SL (paraquat) can be used to kill volunteer corn that emerges before planting.
POTENTIAL YIELD LOSS
Volunteer corn leads to significant yield loss in soybeans and corn.
University of Nebraska-Lincoln research -- https://cropwatch.unl.edu/… -- shows that volunteer corn density of 3,500 plants per acre led to a 10% yield reduction in soybeans. Doubling the density led to a 27% yield reduction.
A recent UNL research study found the highest yield reduction occurred when volunteer corn was left uncontrolled or when it was controlled too late at the R2 soybean growth stage. The combined density at this greatest yield reduction was at 24,710 volunteer corn plants per acre plus 1,235 volunteer corn clumps per acre.
UNL research found a volunteer corn population of 3,500 plants per acre resulted in a 2% yield reduction in corn. Doubling the density caused a 5% yield reduction.
Clumps of volunteer corn led to greater yield loss as they were more competitive than individual plants. A density of 7,000 clumps of corn per acre resulted in a 14% yield loss compared to a 5% yield loss with individual plants.
For more information about volunteer corn control, check out www.dtnpf.com/agriculture/web/ag/crops/article/2021/03/23/manage-volunteer-corn-derecho-fields.
For a story on antagonism, see https://www.dtnpf.com/….
Matthew Wilde can be reached at firstname.lastname@example.org
Follow him on Twitter @progressivwilde
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