A new study featured in the most recent issue of the journal Weed Technology shows that cover crops can help to fight glyphosate-resistant Palmer amaranth — the most difficult of the glyphosate-resistant weeds — to manage a significant problem for U.S. cotton growers.
Cover crop residues create an unfavorable environment for weeds by reducing the light and moisture available to germinating weed seeds. Pre-emergence herbicides are typically used in combination with cover crops, though, to achieve adequate weed control.
Researchers at the University of Tennessee set out to identify which integrated herbicide and cover crop system offers cotton growers the greatest early-season Palmer amaranth control. The cover crops in the study included cereal rye, crimson clover, hairy vetch, winter wheat and a combination of grass and legume. A residual pre-emergence herbicide — either fluometuron or acetochlor — was applied to test plots once the cover crops were desiccated and cotton crops were planted.
In the first 2 weeks of the study, researchers found that the grass and legume combination produced the most biomass and reduced emergence of glyphosate-resistant Palmer amaranth by half compared to test plots with no cover crop. The least impactful cover crops were crimson clover and hairy vetch.
Cover crop plots treated with fluometuron or acetochlor provided greater control of Palmer amaranth, with the two herbicides performing similarly. At no point in the study, though, did cover crops used in conjunction with pre-emergence herbicides provide complete control.
“While there is no single solution for season-long control of glyphosate-resistant Palmer amaranth, cover crops used early in the growing season in conjunction with pre-emergence herbicides can help growers diversify their weed management practices to improve sustainability,” says Larry Steckel, weed scientist at the University of Tennessee.
Full text of the article, “Evaluating Cover Crops and Herbicides for Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri ) Control in Cotton,” is now available in Weed Technology Vol. 30, Issue 2, April-June 2016.