Planning for Next Year's Crop of Weeds

Brenda Frick, Ph.D., P.Ag.

Now is the time to consider which weeds will be problems in the coming year. This will help you devise a strategy to deal with them this spring.

What weeds will this coming year bring? The most reliable prediction about what weeds to expect comes from looking backwards. Most weeds have some dormancy, and will continue to come back for several years after an outbreak. Reviewing field histories will identify the possible candidates for this year's most wanted list.

If we could predict the weather, we would have a good start on predicting the weeds, and how well they will grow. Weeds differ in the way that they respond to temperature. So do crops. The relative difference often determines which has the advantage. For instance, in a spring when moisture doesn't come until the ground has warmed up, green foxtail on the surface can germinate quickly and get ahead of the deep-seeded crops like pea or lentil. In a cool wet spring, wild oats can be up before most cereal crops. Of course, some weeds have been up and at it long before seeding. If these are not set back, they can have a severe impact on the young spring-seeded crop.

If you know the timing of weeds it is easier to manage them. The following table gives some useful information. For instance, if wild oats are a common problem, early season tillage and delayed seeding may control the first flush of wild oats, and place the crop in the ground when it has an advantage. If green foxtail is a more likely problem, seeding early (provided that there is moisture) may allow the crop to get going before green foxtail can germinate. If the major players are perennial weeds like Canada thistle, or winter annual weeds like stinkweed, including winter annual crops like winter wheat or winter rye, biennial cover crops such as sweet-clover, or perennial forages can provide additional fall and early spring competition, and help keep those weeds down.

Unfortunately, the adjustments work both ways. For instance, if your usual practice is to seed as early as possible, you may have pretty good competition against the weeds that germinate only when the soil warms up. But you may be favouring weeds that germinate early. You may notice that, over time, those types of weeds are getting more and more abundant. Weeds adjust to farm practice whenever it is consistent. By varying your practice, and especially by using sound crop rotations, you can be sure that one particular weed pattern will not always have an advantage.

In organic systems, as in all of farming, the weeds will always be with us. Organic weed management is an important focus for me at for the Organic Agriculture Centre of Canada. I would love to hear about your weed challenges and successes. Please contact me at 306-966-4975 or via email brenda.frick@usask.ca

Brenda Frick, Ph.D., P. Ag. is the Prairie Coordinator for the Organic Agriculture Centre of Canada.

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This article first appeared in The Western Producer, and is published here on the OACC website with permission.