Herbicide Carryover? Here’s How to Check.

Apr 10, 2024

soil in flower pot
The potential for carryover injury from herbicides used during the 2023 growing season may or may not be a concern in 2024. Last year was unusually dry in most of Federated’s growing areas, but last fall’s rain and this spring’s moisture may have eliminated the need for concern.
Tim Stelter, Federated’s agronomist and Osceola location manager, said, “Carryover injury is determined by several factors”: 
  1. persistence of the herbicide,
  2. herbicide rate,
  3. soil characteristics,
  4. amount of rainfall during the season following the application,
  5. length of interval between herbicide application and planting the rotational crop, 
  6. sensitivity of the crop to the herbicide, and
  7. early-season crop vigor.
Products that have half-lives sufficient to result in occasional carryover include atrazine, chlorimuron, clopyralid, cloransulam, fomesafen, imazethapyr, isoxaflutole, and mesotrione. 
Kevin Carlson, Federated’s agronomy manager, noted that some Federated growers have specifically mentioned their concern about mesotrione carryover after their corn crop.
Growers who applied herbicides that might have carryover have a few options:
  1. Plant corn again this year (skip the rotation to soybeans).
  2. Switch to a three-way stack soybean, such as LLGT27, which is completely resistant to group 27 herbicides (such as mesotrione). “You can feel comfortable with these,” said Carlson. 
  3. Do an at-home bioassay test to check for carryover in the soils of your field(s):
    • Collect a sizable soil sample from the field of concern – enough to fill a “flower” pot – and plant a few soybean seeds in it.
    • Fill a second “flower” pot with fresh potting soil and plant a few soybean seeds in it as a control/comparison pot.
    • Symptoms of herbicide carryover should appear at emergence, in about 7 days. Carryover herbicide is a pigment inhibitor, and the emerging plants will show whitening or yellowing (in varying shades).
    • The plants that emerge in healthy soil will be green.
Carlson emphasized that he (and the other agronomists) have not tested area soils for carryover, so they do not personally know if there is or isn’t an issue this year.
Your Federated Agronomist will be happy to help you sort through these decisions.

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