Are we losing our focus on weed control?

Tuesday, December 8, 2015

Herbicide-resistant weeds are not going away and will likely get worse. But there are strategies for dealing with them that we need to look at

by PAT LYNCH

When I was a kid on the farm, I remember a pasture field that was visible from the road and which had Canada thistle growing in it. A neighbour came over and suggested it should be clipped. So my dad hooked onto the mower and clipped it. I also remember the stigma of having mustard flowering in a grain field. So one of our jobs was pulling mustard.

In the 1970s, velvet leaf was a terrible weed. You could see it spread from farm to farm. And, since it grows above any crop, it was visible. There were numerous coffee-talk gossipers who put public pressure onto growers to control it.

When triazine-resistant weeds first occurred, we knew where they were. There was a map that pinpointed them. If you were smart and lived near those farms, you took action to delay when they came to your farm. There was a stigma attached to those producers who had the first of these weeds.

Right now, glyphosate-resistant weeds are abundant in Ontario. Those who have them are causing those without them increased costs. If we knew who had the resistant weeds, we could put together individual programs to control them. Because there is a lot of rented land, it would be nice to know where these resistant weeds are.

What is the solution? Well, we could set up a system whereby resistant weeds are recorded on a provincial map. This would have to include the exact location where they are. Not sure we can get this.

Another option is to listen to local chatter and figure that, once a resistant weed is in your area, then you have to spray to control it. This is the case with glyphosate-resistant fleabane. Every Ontario grower now needs to have a strategy to control it.

A third strategy is to scout all your fields or pay someone to do it, and try to get on top of the first resistant weeds.

So will resistant weeds go away, stay the same or get worse? They will get worse. We will have more weeds resistant to glyphosate and other herbicides. The advent of corn and soybeans that have resistance to 2,4-D and dicamba is a help. But the first resistant weeds in Ontario were resistant to 2,4-D. These were wild carrot. The cause was continued spraying roadside by governments to control weeds. It is unreasonable to believe weeds will not become resistant to another group of herbicides.

In Australia, resistant weeds are so bad that growers have reverted to burning and/or plowing 12 to 14 inches deep to bury the seeds.

However, there is another strategy and this includes tillage. Organic farmers are doing a reasonably good job of controlling annual weeds with tillage. I think there are lots of opportunities to do more. I have never heard of a weed that is resistant to iron.

Cover crops also help weed control. If you have land with nothing growing there for weeks, weeds will grow. The more they grow and reproduce, the higher the probability that they will change so that the resistant ones will increase.

The strategy we used to use was employing weed "gleaners" (separators) on combines. There was a separate area for collecting weeds. Companies went away from weed gleaners or separators because it reduced the capacity of the combine and added cost. We need them back. The best way to spread resistant weeds is with a combine.

There is no doubt we have to increase our focus on controlling weeds, both on your own land and land around you. BF

Consulting agronomist Pat Lynch, CCA (ON) formerly worked with the Ontario agriculture ministry and with Cargill.