KindHarvest summary: Weed scientists warned in 2022 that Palmer amaranth populations in parts of the US Mid-South were becoming less sensitive or resistant to several herbicides. The pattern threatened the reliability of programs that had depended heavily on a small number of active ingredients.
What researchers were seeing
University of Tennessee weed scientist Larry Steckel reported greenhouse populations surviving high dicamba rates, with some cross-resistance to 2,4-D and signs of metabolic resistance. Mississippi State University specialists described how resistance can range from partial control and regrowth to almost complete failure.
Metabolic resistance is especially concerning because a weed may detoxify several herbicides through broad biological mechanisms. Repeated reliance on one effective component within a tank mix can also place heavy selection pressure on that chemistry.
Implications for management
The report called for closer monitoring of what still works and a broader weed-control program. Residual herbicides, crop rotation, competitive crops, cover crops, mechanical or harvest controls, sanitation and preventing seed return can all reduce dependence on a single mode of action.
Resistance patterns change by field and region. Growers should confirm suspected failures, keep application records and use current local extension guidance when building a program.
Related KindHarvest reading
Cover-crop biomass can add physical suppression to an integrated weed program. Read the KindHarvest brief on cereal rye biomass and waterhemp.
Source and credit
This KindHarvest Team news brief is based on reporting by Forrest Laws for Farm Progress, published 29 June 2022. Read the current Farm Progress article.