Herbicide resistance is a very real threat to our ability to effectively control weeds in amenity situations and groundsmen need to take steps to avoid it, warns Monsanto.
Technical Development Manager Barrie Hunt explains: “There are currently no known cases of glyphosate resistance in the UK, however, globally, resistance has evolved as a result of repeated use and over-reliance on this active ingredient.”
In Europe, resistance has been confirmed in two plant families and six species. They are the Fleabane (Horseweed) speciesConyza bonariensis, Conyza canadensis and Conyza sumatrensis, and Ryegrass speciesLolium rigidum, Lolium perenne and Lolium perenne var. multiflorum.
Barrie comments: “Fleabane, or Conyza, resistance has developed in amenity situations, including railways and roadsides, as well as in perennial crops. Ryegrass resistance has occurred predominantly in perennial crops and also in arable farming.”
“Ryegrass resistance has not been found in specific amenity situations, however many perennial crop situations directly mimic practice in amenity.”
Development of resistance in Europe is mainly due to repetitive or inappropriate practices, he explains:
“These practices include over-reliance on of the same herbicide i.e. glyphosate, not following label recommendations and a lack of, or limited, Integrated Weed Management strategies.”
Minimising the risk of resistance is based on Good Plant Protection Practice and an Integrated Weed Management Strategy, which all groundcare professionals should be carrying out as a matter of routine, but a Resistance Management Strategy should also be put in place.
“Whenever possible, use mixtures of herbicides, and consider integrating non-chemical control measures,” explains Mr Hunt.
“Monitor and assess herbicide performance after spraying to detect any loss in control, - good record-keeping is key to the early detection of resistance.”
Planning applications carefully to ensure that the active ingredient is at its most effective helps to prevent survivors, he emphasises, as repeat applications to surviving plants present the greatest risk of resistance developing.
“If resistance is suspected, contact your supplier and/or the product manufacturer, and act quickly to prevent spread - use a strategy involving alternative herbicides and non-chemical techniques. Then collect seed samples for testing to confirm resistance,” Mr Hunt advises.
“However, by being vigilant, we can hopefully avoid resistance, and help these valuable chemicals to continue to maintain the quality of sporting and leisure facilities.”