Discovering How Pre-Emergence Herbicides Combat Blackgrass

Scientists at Rothamsted Research have unveiled significant differences in how three commonly used pre-emergent herbicides—flufenacet, EPTC, and tri-allate—affect the persistent agricultural weed, blackgrass (Alopecurus myosuroides). The research, published on December 8, 2025, in the journal Annals of Applied Biology, offers crucial insights into the complex biochemical mechanisms that underpin herbicide action against one of the UK’s most troublesome weeds.

Blackgrass has become a major concern for UK farmers, costing millions in lost yields annually. This weed has developed resistance to various herbicide groups, complicating effective management strategies. The study focused on Group 15 herbicides, which inhibit very long-chain fatty acid synthesis, a vital aspect of weed control strategies. Despite their classification, little was known about their specific effects on blackgrass at the physiological or molecular levels.

Unique Effects of Each Herbicide

Through controlled growth experiments and advanced lipid profiling, the research team discovered distinct impacts of each herbicide on blackgrass. The findings include:

– **Flufenacet**: Strongly inhibited both shoot and root growth while significantly reducing wax and very long-chain fatty acid levels, especially in sensitive biotypes.
– **Tri-allate**: Resulted in dramatic decreases in polyunsaturated fatty acids in shoots, indicating a unique mode of action that extends beyond wax synthesis.
– **EPTC**: Displayed milder effects, primarily altering wax composition rather than fatty acid profiles.

Dr. Dana MacGregor, the lead author and a research scientist at Rothamsted, emphasized the importance of these findings. “Although these three herbicides are grouped together, their effects on plant growth and metabolism are different. Understanding these differences is scientifically interesting and aids farmers in selecting the appropriate product for specific situations.”

Co-author Frédéric Beaudoin, a lipid metabolism specialist at Rothamsted, added that the intricate nature of fatty acid and lipid metabolic pathways is interconnected with other metabolic processes. He noted, “Blackgrass’s wax profile is unusual compared to most other grasses. Studying how these herbicides influence it provides insights into their activity and reveals fundamental details about their molecular targets and modes of action.”

Implications for Farmers and Weed Management

The research also highlights the behavior of two distinct blackgrass biotypes: one that is sensitive to herbicides and another exhibiting metabolic resistance. Dr. Hannah Blyth, another lead author, explained the significance of these differences. “There is no evidence of resistance to Group 15 herbicides in blackgrass, but populations from various fields can behave quite differently. Understanding these variations can inform better strategies for sustainable weed control.”

The threat of blackgrass to the sustainability of UK cereal production is profound. By clarifying how Group 15 herbicides operate differently, this research supports more targeted and effective use of pre-emergent herbicides in integrated weed management practices.

Industry partner Laurent Cornette from Gowan Crop Protection remarked on the practical implications of the study, stating, “For farmers, these findings enhance confidence in the combination of different pre-emergence herbicides from Group 15. This group encompasses a variety of compounds that share similar physiological effects but differ in their modes and sites of action.”

The study’s revelations are timely, considering that no cases of target-site resistance have been reported for Group 15 herbicides. This characteristic positions them as low-risk resistance compounds, potentially aiding in the preservation of the efficacy of other herbicide groups and delaying the development of resistance.

In conclusion, the research conducted by Rothamsted Research not only deepens the understanding of herbicide action against blackgrass but also paves the way for more effective strategies in the ongoing battle against this resilient weed.