BEAUMONT, Alta. — Organic farmers must use all the tools at their disposal to kill weeds growing in their crops, said a University of Saskatchewan weed scientist.
However, the first year of a study found that organic farmers who use a combination of weed reduction strategies can achieve almost the same level of weed control as farmers who use herbicide, Steve Shirtliffe told farmers at the Organic Alberta conference.
“In order to get a herbicide registered, you need to show 80 percent control. Using agronomy and mechanical weed control, we are almost getting as good of control as you can with herbicide,” he said.
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“We were very happy with this study.”
Organic producers need to rely on a combination of modern and old-fashioned technologies to beat back weeds.
Shirtliffe’s study used a combination of post-emergent harrowing, low and high seeding rates, varied row width and competitive and non-competitive crop varieties to find the best way to control weeds.
“Put all this together, we had an increase of 25 percent in our yield and decreased weed biomass by 70 percent,” said Shirtliffe.
Seeding at high rates increased yield by 11 percent and reduced weed biomass by 52 percent.
Seeding one and a half times the recommended seeding rate will give the greatest weed suppression, he said.
In-crop harrowing when the weeds were at an early stage reduced weeds by 50 to 60 percent and increased yield by 13 percent.
Not all crops or weeds respond to harrowing. Deep rooted weeds such as wild oats are not easily torn from the soil by harrowing, while barley and oat crops can stand to be partially covered by soil during harrowing. Wheat is the least tolerant cereal to being covered in soil after harrowing.
“If you’re covering up too much of your plants, that’s a bad thing.”
Rotary hoes are an effective tool to manage weeds in the early white thread stage when weeds are not anchored into the soil, he said.
“The effectiveness depends on timeliness.”
Growing varieties that jump out of the ground quickly and are competitive with weeds is the other key to controlling weeds in organic crops. A good competitive crop can reduce weed biomass by 22 percent.
A nine-inch row spacing seemed to be the ideal spacing to help improve competitiveness.
