“Everything is very short term, but combining practices can give long term benefits”
Herbicides have pretty much been a magic bullet for controlling weeds since their introduction in the 1950s, but increasing resistance, cost and public concern over residues are encouraging growers to seek alternatives.
Kristina Polziehn, manager of agronomic services at Viterra, told the Grande Prairie Farm Women’s conference here in November that western Canadian growers spend about $500 million a year million fighting wild oats, which are rapidly becoming resistant to Group 1 and 2 herbicides. That’s prompted an increased focus on integrated weed management (IWM). Polziehn said IWM has been around since the 1970s but is still in its infancy in Western Canada and will develop based on the experience of growers.
“The objective is to develop economical, and ecologically sustainable cropping systems,” said Polziehn.
The process is a holistic system which uses biological knowledge of weeds and combines them with agronomic practices which can improve the competition and diversity of crops while reducing the stability of weed communities. No single integrated weed management strategy will be appropriate for all growers at all times. The best strategy will always depend on choice, economic options and the growers’ attitudes and beliefs, said Polziehn.
Combining a variety of agronomic practices is also a way of practising integrated weed management. “Everything is very short term, but combining practices can give long-term benefits,” said Polziehn.
Direct seeding, crop rotation, using competitive crops and cultivars and changing seeding dates and rates can all be part of an integrated weed management system. Direct seeding can improve soil quality and allow for more conservation of moisture by reducing soil erosion. It also improves water infiltration and increases the organic matter in the soil.
WEED POPULATION SHIFT
The adoption of direct seeding has led to changes in herbicide use and a shift in weed communities, said Polziehn. Direct seeding allows producers the opportunity to exploit weed seed banks. Soil is flipped on the weed seeds, which remain in the top two inches of the soil, where they can be eaten by mice, beetles and microbes.
She said cover crops crops such as winter rye can be added to conventional systems to provide ground cover for crops such as potatoes and sugar beets. Green manure also helps suppress weed competition and enhances the available nitrogen in the soil.
One of the most valuable tools is an integrated weed management strategy is crop rotation, said Polziehn. “We can help reduce some of our financial risk by rotating crops, decrease disease incidence, improve soil quality and increase nutrients and moisture reserves,” she said. Unfortunately, crop rotation is sometimes affected when one crop is fetching high prices while another is at a low, said Polziehn.
However, rotation disrupts the life cycle and growth habits of weeds and forces a change in seeding and harvesting dates. Growing different types of crops can also alter the timing of seeding and herbicide applications.
Early seeding can also be part if integrated weed management. Early seeding can minimize the risk of heat stress during flowering, and early-seeded crops can sometimes compete against weeds that require warmer soil temperatures.
Polziehn said early seeding is not possible in all regions of the province, but it can be combined with early weed removal in order to maximize weed control and crop yield.
Early crop emergence can also provide crop competition for late-emerging weeds, said Polziehn. If moisture is available, an increased seeding rate may be able to improve the competitiveness of the crops against the weeds and enhancing the seeding rates can also improve the efficacy of herbicides.
Polziehn emphasized that higher seeding rates should never be used on malt barley, as the plumpness of the kernels is reduced.
The cultivation of silage, cover crops and green manure also increase the diversity of crop rotations and help to manage weed populations. “The combination of early-cut barley silage without herbicides can be effective in reducing wild oat populations,” she said.