Guidelines for minimising the risk of glyphosate resistance development published by the Weed Resistance Action Group (WRAG) are just what UK growers and agronomists need to safeguard the single most vital weapon in their grass weed control armoury. As such, these guidelines should form the essential basis for all glyphosate use from now on.
This is the uncompromising view of glyphosate stewardship leader, Barrie Hunt of Roundup who has been actively involved in the guidelines’ development with some of the country’s foremost weed control experts.
“Despite being commercially available for over 40 years and used increasingly widely in almost every sector, the guidelines recognise that no resistance to glyphosate has so far become apparent in the UK,” he stressed.
“Yet resistance is known to have developed in other parts of the world. This and the pivotal value of glyphosate in the face of growing resistance to almost every other piece of herbicide chemistry we have today makes it imperative to do everything we can to sustain this position.
“All the more so since there are so many different glyphosate products currently approved for professional use in the UK based on an array of different salts, loadings and adjuvant mixtures and contents. This makes less-than-ideal usage and the less-than-effective treatment which are key drivers of resistance development more of a risk.
“Also worrying is the fact that European laboratory analyses of a random sample of more than 70 generic glyphosates have highlighted wide variations in both active ingredient and surfactant contents – many below stated levels and outside accepted tolerances.”
Under these circumstances, Barrie Hunt welcomes the guidelines’ insistence on using glyphosate with particular care, emphasising the importance of always understanding exactly which product is being used, employing it at the correct dose rate for the job, and applying it at the correct growth stage of the target weeds and in the right way.
He points out that annual grasses typically require 540 g/ha of glyphosate to control seedlings of up to six tillers and 1080 g/ha when flowering, insisting that adjuvants will not make up for any lack of active ingredient in most situations.
“Regrowth as a result of incomplete kill is the fastest route to resistance development as well as a waste of time and money,” he said. “Getting your glyphosate use right first time makes sense whichever way you look at it. Especially when both time and finances are as tight as they are today.
“In addition to dose rates and timing, the WRAG guidelines provide valuable advice on water volumes, spray quality and the use of water conditioners. They also make the important point that multiple stubble or stale seedbed applications without cultivation between them – as a belt-and-braces to ensure no survival of treated plants – should be avoided. And they urge the integration of glyphosate with other cultural and chemical controls as widely as possible.
“After 40 years on the market, one of the biggest dangers with glyphosate use is complacency,” Barrie Hunt concluded. “The products of today are very different from the old familiar 360 of the past. Modern Roundups, in particular, are much more effective, rainfast and flexible to use under a wider range of conditions and have important elements of stewardship built into them for easy and responsible use. Even so, the guidelines provide a timely reminder that they – as well as less effective formulations – need to be used with sufficient care and understanding if we are to preserve glyphosate for the future while making the most of it today.”