The use of herbicides has always been an effective, and even essential, component of zero till systems. Up to now, strategic use of chemical weed control throughout the crop season has meant that zero till farmers have been able to keep fields clean without tillage.

Since zero tillers depend more heavily on post-emergence products, (and Group 1 products specifically), it might be argued that this problem is a bigger concern in zero till than in conventional tillage.

That's a fallacious argument, though. Group 1 resistance will ultimately be the biggest threat to farmers who ignore it - regardless of whether they are zero tillers or use conventional tillage.

Take the two worst weeds in the eastern prairies (wild oats and green foxtail); add in the best 11 or 12 herbicides you've got for control of these weeds (Group 1 chemicals); now pretend you live in a world where these chemicals no longer control these weeds on your farm.

In July of 1990, that's the world that weed specialists from MDA and U of M discovered in a field near Swan River. The farmer in that instance had a wild oat population that was resistant to 30 times the field rate of products listed in Table 1.

Since then, we've gone from one confirmed case of Group 1 resistant wild oats, to over 70 cases in Manitoba. Since 1991, we've gone from no reported cases of Group 1 resistant green foxtail, to 20 cases.

These are small numbers when you consider that we have 15,000 plus farmers in Manitoba. But what is truly alarming is the number of farmers who are using Group 1 products year after year on the same fields and are following the same path to be problem. In terms of market share, 15 out of 16 acres of flax are treated with Poast, Select, Assure or Fusilade - all Group 1 products. In cereal crops such as wheat and barley - 65 per cent of sprayed acres are treated with Achieve, Triumph Plus or HoeGrass - all Group 1 products.

This massive shift over to Group 1 products means that our original 100 farmers with the resistance problem now will have lots of company very soon!

Practical results from the accumulated experience of farmers who have this problem, and computer modeling, give us a solution. You can delay the onset of resistance to Group 1 chemicals no more frequently than one year in three on the same field.

Again, this delays the onset of resistance - hopefully long enough for industry to "fire up the corning ware" in their labs and come up with new products with new modes of action.

Following this " 1 on - 2 off" regime is no small order for any farmer. By staying away from Group 1 products for two years, you effectively surrender the annual "one-shot" wild oat/green foxtail control you've come to enjoy. No other post-emergence product controls both of these weeds in one pass.

Forward planning two or three years ahead will become necessary, with Group 1 products used as your "ace-in-the-hole" to beat back grassy weed populations - perhaps in your last competitive crop.

In any case, it is apparent that we are going to have to come to terms with the fact that when we do battle with weeds, we do battle with Mother Nature. The brute force of using highly effective chemistry year after year shows Mother Nature a pattern - a pattern to which she is adjusting. We must rethink our use of products so that we may preserve them for our use.

TABLE 1