9 August 2002

Weeds build up herbicide resistance

OVER 20 weed species are showing resistance to a range of herbicides, according to a recent farmer survey.

For the first time, the annual survey shows a number of farmers identifying resistance in chickweed. Two-thirds of farmers with resistant blackgrass said it was associated with fop and dim contact herbicides.

Farmers responding to the National Crop Weed Survey also perceived that sulfonyl-ureas recommended for blackgrass control may be suffering resistance problems already.

Common chickweed resistant to some sulfonyl-urea herbicides was identified on farms in Northern Ireland and Scotland.

With over half of all blackgrass resistance cases first reported just two years ago, the NFRU says the problem is escalating.

"Farmers must be aware of the high risk of resistance to newer herbicides and to new weeds," says Mike Heisig of the NFRU. "They must adopt measures to retain the armoury of chemicals that we need to control weeds in the future."

&#8226 See Herbicides Supplement for more weed control advice. &#42