29 May 1998

Herbicide resistance warning

FARMERS who rely too much on the rising number of sulfonylurea herbicides could be storing up weed control problems for the future, warns a UK herbicide expert.

Many such herbicides are now available and over-use could cause herbicide resistant broad-leaved weeds, advises Stephen Moss of IACR-Rothamsted, Herts.

So far the UK has escaped trouble, mainly because growers use herbicides with different modes of action. But elsewhere the near exclusive use of sulfonylureas over a number of years has led to trouble, he notes.

Like "fop" and "dim" herbicides sulfonylureas can soon induce resistance if used frequently, Dr Moss notes. That contrasts with mecoprop, which can be used regularly for far longer with no problems.

Cases of sulfonylurea resistance include chickweed in Ireland and Denmark and poppy in Spain. In each case resistance is probably target site type, resulting in herbicide failure. Resistance to one type of sulfonylurea may mean resistance to all sulfonylureas and in some cases there could be cross resistance to herbicides with other modes of action, Dr Moss explains.

"There is a risk of resistance to the sulfonylurea group arising. But I dont want to exaggerate it. My message to growers is simply not to place sole reliance on members of this group," declares Dr Moss. &#42