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Herbicide Carryover This Spring

Herbicide Carryover This Spring

Given the dry conditions that prevailed Iowa in 2023, there will be herbicide carryover in 2024. Suspect herbicides that are likely to carryover include, but are not limited to atrazine, clopyralid, and the various HPPD inhibitor herbicides. Specifically, the accuracy, evenness, and timing (i.e., later in the season) of the 2023 herbicide applications can increase the potential for interactions with the 2024 herbicides.

However, just because herbicide residues exist in the soil does not mean that crops will succumb to herbicide injury. If spring conditions are not stressful to the 2024 crop, herbicide injury may not occur. Extremes in soil moisture and/or temperatures that cause crop stress increase the chances that herbicide carryover injury will occur. Stress from herbicides applied in 2024 can also additively cause additional stress resulting in herbicide carryover symptoms.

Generally, herbicide carryover is seen in isolated areas in fields. Areas with low organic matter, high pH, or where herbicide rates are high due to application issues are likely to have herbicide carryover injury. While bioassay testing is mentioned as a tactic to better understand the potential for herbicide carryover, given the spotty nature of areas where herbicide carryover is found, the accuracy of the bioassays is questionable. Often the results are false positives or negatives.

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Photo Credit: gettyimages-mvburling

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