Black-grass with reduced sensitivity to glyphosate detected

Early signs of decreased sensitivity to the herbicide glyphosate have been detected in several black-grass field populations in England.

The project, led by Rothamsted Research, also found that decreased sensitivity was more likely in fields where populations had been exposed repeatedly to glyphosate. The scientists also showed clearly that offspring from plants that survived glyphosate application were even less sensitive to the herbicide.

Although no UK black-grass populations are classed as resistant (i.e. weeds should still be controlled by well-timed applications at the full label recommended rate), the potential for resistance to establish and spread has been demonstrated clearly. People are reminded to follow the guidelines issued jointly by AHDB and the Weed Resistance Action Group: ahdb.org.uk/wrag

The study used material gathered by the black-grass resistance initiative. The work was funded by the Biotechnology and Biosciences Research Council (BBSRC) and AHDB.

Further information on the research results can be accessed via the Rothamsted Research news release.

AHDB has also invested in a five-year programme of work to improve glyphosate resistance management guidelines. The work, which concludes next year, focuses on the main glyphosate application periods for the control of black-grass and Italian rye-grass.

key messages

1. Prevent survivors: Avoid repeat applications to surviving plants
2. Maximise efficacy: Apply the right dose rate* (reduced rates increase the risk of reduced efficacy), at the right timing, in the right conditions
3. Use alternatives: Use non-chemical options (such as cultivation), where practical, and use other herbicides in sequence
4. Monitor success: Remove survivors and report potential resistance issues to your advisor and/or the product manufacturer

*In relation to dose, current guidance states that annual grasses typically require 540 g a.i./ha for seedlings up to 6 tillers.