You must become your own weed inspector

Wednesday, October 6, 2010

There was a time when townships took care of roadside weeds, but no more. Now you must do the job yourself and it pays to start when they first appear on your farm

by PAT LYNCH

The Ontario government has set up a committee to look at invasive weed species and you might think this would help you reduce the number of problem weeds on your farms. It probably won't. It is intended more to look at weeds like giant hogweed and poison ivy  that are threatening townspeople since the introduction of legislation to reduce herbicides in urban areas.

In the meantime, Ontario farmers are battling weeds that are invading from various areas, such as roadsides. Numerous farms are battling hard-to-kill weeds like wild carrot, colt's foot, bur cucumber and purslane. There was a time when the townships sprayed these and had weed inspectors to deal with problem weeds. Those days are gone.

Because of changes to the system, you must become your own weed inspector. That means identifying particularly nasty weeds and spraying them at the appropriate time. You cannot make a general herbicide application to a roadside and expect to kill everything. The time to kill bur cucumber is different than when you must kill wild carrot.

Wild carrot is best controlled in early September. This weed is interesting in that it was the first recorded resistant weed in Ontario. Because of widespread use of 2,4-D on roadsides, the 2,4-D -resistant biotypes started to emerge. Now wild carrot has become troublesome in many no-till soybean fields.

Bur cucumber is also very aggressive. It can be controlled as a seedling, but once it gets to a certain size it becomes very hard to kill. It grows on roadsides or ditches and spreads into the field. Once in the field, it drops seeds which makes sure it grows again next year. This weed is so aggressive it can kill a growing crop. It is a bad one.

Another source of invading weeds are those that are resistant to herbicides. The newest group are ones resistant to glyphosate. Probably the most recent were the group 2 resistant weeds.

The current crop of glyphosate-resistant weeds has been kept pretty secret. The growers who have them are embarrassed and do not want to be identified publicly. Those concerns must be acknowledged. But the concerns of growers who do not have these resistant weeds also must be acknowledged. We know combines do a beautiful job of spreading weed seeds. We know these seeds can travel miles in a combine. If I was farming in an area, I would want to know who had those resistant weed so that, if they were farming next to me, I could be extra vigilant and take precautions to prevent the spread on to my farm.

The Insect Resistant Management Program encourages growers to use responsible stewardship so that resistance does not happen when using Bacillus thuringiensis to control corn borer. If growers do not adhere to that strategy, they could lose access to the technology.

There is no similar weed management strategy. The cost of weed resistance to individual growers is greater than will be the cost of insect resistance. Maybe the Ontario Soil and Crop Improvement Association could spearhead a program to help pinpoint these new nasty weeds.

So try to become your own weed inspector. Controlling weeds is expensive. The best way to reduce this expense is to control the weeds when they first appear on your farm. BF

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