It's a simple management step that could pay large dividends for Canadian canola producers. Researchers at the University of Alberta and Agriculture and Agri-Food Canada are pinpointing strategies for farmers to lower their risk of pest infestation by reducing herbicide application rates.

Previous studies suggest lowering herbicide rates to retain a small base of late-emerging weeds can deter pests without negative impact on yield and other aspects of crop performance, says Dr. Lloyd Dosdall. A new, three-year study will determine herbicide application rates that produce the best overall results for crop producers. The study is supported in part by the Endowment Fund, administered by Western Grains Research Foundation. (Read the research report: www.westerngrains.com/endow/2004_02.html)

"Late-emerging weeds usually have little negative impact on yield, and their contribution to the weed seed bank in soils is often insignificant; nevertheless, many growers apply herbicide to control these weeds," says Dosdall. "Our research aims to investigate the benefits of reducing those application rates, to allow a small base of late-emerging weeds. Late-emerging weeds can provide a home for natural enemies of insect pests. By increasing diversity, they can also lower the risk of disease and pest infestations."

With a small base of weeds, infestations of root maggots, diamondback moth and sclerotinia stem rot should decline, he says. This will result in improved environmental and economical sustainability by reducing crop damage and improving herbicide efficiency, he says. The key to succeeding with this strategy is determining the level of weedy background that helps reduce insect and disease pests without having a significant negative impact on crop growth.

"The greatest challenge of this project will be finding the optimal balance between the crop plants and the weedy background. We want enough weeds to preserve the beneficial effect of reducing the incidence of insect and disease pests. But we don't want a level of weeds that robs the crop plants of water and nutrients."

The project's approach is based on the concept of Integrated Crop Management (ICM), says Dosdall. ICM is a knowledge-based strategy for how to farm. It asks producers to look at all their production goals and challenges as a whole, and to draw on the best combination of available knowledge and tools to maximize their success.

"ICM is basically a holistic approach," says Dosdall. "Rather than looking for single solutions to single problems, the idea is to take a broader look at interactions and develop an overall strategy that best meets a combination of goals. For example, if you look only at weed removal as a goal, you risk losing the pest reduction benefits of a small base of weeds. A better strategy is to find a balance between weed control and pest control."

The project will begin in April 2004 with the seeding of plots at Lacombe and Beaverlodge, Alta. Researchers will plant two different species of canola - Brassica napus and Brassica rapa - along with tame oats, which will provide a base of weed presence in the field. Researchers will monitor plant growth while applying herbicide at various stages and rates.

Throughout the growing season researchers will gather data on the various insects and diseases that enter the fields. Following fall harvest, they will collect further information on yield and dockage, as a basis to conduct an economic analysis.

"We anticipate that fewer herbicide, insecticide and fungicide applications will enhance economic returns," says Dosdall. "But we can't and won't recommend anything to growers that isn't economically valid." If results point to the need for further pesticide applications, the team will outline optimal timing of applications that will minimize the harmful effects on natural enemies of pests.

Although the project will focus on canola production, Dosdall says the research has implications for similar ICM practices used on a variety of cereal and pulse crops.

More of Dosdall's views on ICM will be featured in the March edition of Western Grains Research Magazine, available beginning March 1 on the WGRF Web site, www.westerngrains.com. The WGRF Endowment Fund has allocated over $17.5 million to more than 200 research projects since its inception in 1983.

Read the research report: www.westerngrains.com/endow/2004_02.html