New Study Reveals How Key Pre-emergence Herbicides Differ in Action Against Blackgrass

Scientists at Rothamsted Research have discovered that three widely used pre-emergent herbicides - flufenacet, EPTC, and tri-allate - affect blackgrass (Alopecurus myosuroides) in strikingly different ways. The findings, published in Frontiers in Agronomy shed light on the complex biochemical mechanisms behind herbicide action in one of the UK’s most persistent agricultural weeds. By revealing how Group 15 herbicides act differently, this work supports more targeted and effective use of pre-emergent herbicides in integrated weed management.

Blackgrass costs UK farmers millions in lost yields each year and has evolved resistance to multiple herbicide groups, making effective control increasingly challenging. Group 15 herbicides, described as those that affect shoot growth by inhibiting very long-chain fatty acid synthesis, are a cornerstone of weed control strategies. However, there were always questions on whether this generic label was appropriate as until now, little was known about how these herbicides affect blackgrass at the physiological or molecular level.

Using controlled growth experiments and advanced lipid profiling, the team found that:

• Flufenacet strongly inhibited both shoot and root growth and reduced wax and very long chain fatty acid content, particularly in sensitive biotypes.
• Tri-allate caused dramatic reductions in polyunsaturated fatty acids in shoots, suggesting a unique mode of action beyond wax synthesis.

• EPTC had milder effects, altering wax composition more than fatty acid profiles.

  “Looking at physiology or metabolism, it is clear these herbicides don’t all work the same way,” said Dr Dana MacGregor, lead author and Research Scientist at Rothamsted. “Although these three herbicides are grouped together, their effects on plant growth and metabolism are different. Understanding these differences is not only scientifically interesting, but it also helps farmers and agronomists choose the right product for the right situation.”

Co-author Frédéric Beaudoin, a lipid metabolism specialist at Rothamsted, added:

“Fatty acid and lipid metabolic pathways are complex and interconnected with other metabolic processes. Blackgrass’s wax profile is unusual compared to most other grasses. By studying how these herbicides influence it, we not only learn about their activity but also gain fundamental insights into their molecular targets and Mode of Action (MoA), which we now believe to be more complicated than initially thought.”

Industry partner Laurent Cornette from Gowan Crop Protection commented:

“For farmers, these findings strengthen the confidence with which we can combine different pre-emergence herbicides from Group 15. Group 15 encompasses a broad range of compounds that share the same physiological effect but differ in their modes and sites of action. Notably, no cases of target-site resistance have ever been reported for Group 15 herbicides, giving them a distinctive status as low-risk resistance compounds. Their use can therefore contribute to preserving the efficacy of other herbicide groups by helping to delay resistance development.”

The study also compared two blackgrass biotypes: one herbicide-sensitive and one with metabolic resistance. Responses varied significantly between them.

“There’s no evidence of resistance to Group 15 herbicides in blackgrass, but populations from different fields can behave very differently,” explained Dr Hannah Blyth, lead author on the paper. “Studying these differences gives us insight into how physiological, genetic or metabolic traits shape herbicide responses and helps us design better strategies for sustainable weed control.”

The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and supported by Gowan Crop Protection Limited.