What is driving glyphosate resistance?
Thirty-five different weed species are now resistant to glyphosate-based herbicides in countries around the world - and the list continues to grow.
In the UK and Ireland, Italian ryegrass has recently been added to this list.
The glyphosate issue is a touch point within the wider challenge of herbicide resistance within both arable and grassland farming systems.
Adding to the pressure on farmers and contractors is the fast-diminishing range of agrochemicals they can use to control weeds in crops.
This subject was highlighted at a recent National Register of Sprayer Operators (NRoSO) road show, hosted at the Greenmount campus of the College Of Agriculture of Enterprise (CAFRE) in Co. Antrim.
Herbicide resistance
A number of issues have been identified as contributing to the herbicide resistance issue.
These include the growing of the same crop in the same fields on a continuous basis. This approach sees the use of the same agrochemicals on the same weed species year after year.
Introducing more effective crop rotations is one obvious starting point in addressing this issue, according to advisers.
Another factor contributing to the resistance problem is the application of agrochemicals at rates below those recommend by the manufacturer.
In such instances, a proportion of a weed population is allowed to produce seed for the next season, which will have a degree of resistance to the herbicide previously used.
However, this is a very complex issue, as CAFRE crops adviser, Leigh McClean pointed out at the NRoSO event.
He said: “Product specification accounts for 50% of a herbicide’s efficacy.
“The other issues that impact on the effectiveness of a herbicide include tank agitation levels within the sprayer, boom stability and the height of the boom above the crops.
“In quite a number of instances, we could end up with a scenario that sees as little as 10% of the herbicide applied reaching its intended target.”
Minimal cultivation systems have been recognised as heightening the potential for herbicide resistance to get a foothold, in certain instances.
This, in turn, reflects the continuing role for deep ploughing within arable production systesm.
The use of stale seed beds can also be used as a means of coping with high levels of weed infestations.
By using this approach, freshly germinated weed seeds can be killed off using physical cultivation techniques.
Another way of ensuring that resistant weeds do not gain access to farms is by making sure that all machinery is thoroughly cleaned prior to its use at a new location.
