Resistance to herbicides now rampant – IACR
Improved weed control with
less impact on the
environment was the theme
of this years British Crop
conference in Brighton,
which included sessions on
genetically modified herbicide
tolerant crops, new herbicides,
better use of existing products and herbicide resistance.
Over the following pages
Charles Abel, Andrew Blake
and Andrew Swallow report
HERBICIDE resistance is now so widespread in grassweeds that no grower in the UK should assume their farm is resistance free.
That is the view of IACR – Rothamsted weed ecologist Stephen Moss, based on resistance testing data. "The message is that resistance is very widespread with black-grass; we have largely stopped counting."
Wild oat and Italian ryegrass resistance to herbicides is also increasingly widespread, and no farm in the country should assume it is resistance free, even if no resistance has been recorded in that county.
"The important thing is to get a sample tested if herbicide activity is sub-standard. Talk to your crop consultant or advisor about how to do this. It is £25 well spent first so growers know what they are dealing with," he stresses.
"For example, if a grower found he had target-site resistance then he would not want to use any fop or dim chemistry. But if resistance is found to be only enhanced metabolism, some fops and dims could give quite good control."
The data was collated by Dr Moss from resistance results supplied to him by all companies and organisations conducting resistance tests.
"We are not saying every farm has got resistant blackgrass, but a lot of farms have had no tests done at all."
The new "R" system for rating herbicide resistance simplifies categorisation of resistance for all weeds, including blackgrass, wild-oats and ryegrass, continues Dr Moss.
"The star system had too many categories and wasnt appropriate for all weeds. The R system should be easier for growers to understand," he says.
Old system New R System
5*/4* RRR: Resistance
likely to reduce
3*/2* RR: Resistance
1* R?: Early indications
that resistance may be
S S: Susceptible.