Fall or early spring herbicide applications are a great proactive weed management strategy to ensure fields “start clean” at planting, even though additional herbicide applications will be needed for fields to “stay clean" throughout the season. Other benefits include conserving water and removing hosts for pests.
Some weeds to target with these applications include kochia, marestail, and winter annual weeds such as henbit, weedy brome species, and volunteer wheat. Recommended herbicides for these scenarios include products with postemergence activity and residual herbicides. Atrazine has historically been an important part of these programs. However, recent changes in atrazine labels mean that atrazine cannot be used in some fall-applied scenarios.
Companies that label atrazine-containing herbicides have not renewed 24(c) labels in Kansas that allow for fall applications in row-crop stubble. Fall applications to wheat stubble in a chemical fallow system are still allowed.
Alternative herbicides to atrazine
Some herbicides with residual activity to consider in place of atrazine in these applications include Group 14 herbicides like sulfentrazone (Authority, others) or flumioxazion (Valor, Panther, others) and Group 15 herbicides like pyroxasulfone (Zidua, Anthem, and others), S-metolachlor (Dual, others), and acetochlor (Harness, Warrant, others).
Regardless of which herbicides you apply, the postemergence herbicides will work better when temperatures are warm enough for active weed growth. Daytime temperatures in the 40s would be a good minimum temperature for most applications. Another consideration is that herbicides should not be applied to frozen soil. Be sure to check your herbicide label(s) for application requirements specific to your fields.
Additional information about fall herbicide applications ahead of corn and sorghum can be found in this eUpdate article from September and in the 2023 Chemical Weed Control for Field Crops, Pastures, Rangeland, and Noncropland, K-State publication SRP-1176.
The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.
Sarah Lancaster, Extension Weed Science Specialist
slancaster@ksu.edu