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Weed of the week: wild oats

Wild oats have been hurting yields and spoiling tame oat samples for generations. And with increasing instances of herbicide resistance, prairie farmers’ fight with the pest isn’t ending any time soon.

Hugh Beckie of Agriculture Canada’s Saskatoon Research Centre said wild oats remain of the 10 worst annual weeds that cereal producers must contend with worldwide.

Research indicates that more than 10 million acres of Western Canada is affected by herbicide resistant weeds and most of those incidents are wild oat related.

Reduced tillage systems have done much for agriculture in Western Canada and for wild oats as a plant. The need for chemical control in place of steel and diesel fuel has selected for resistant genetics in avena fatua, its Latin name, especially for those chemicals with a single mode of action.

At more than $500 million annually in lost crop yields, wild oats is the leading weed pest with which prairie farmers must contend.

A recent, large-scale study has shown that 20 percent of the fields tested contained herbicide resistant wild oats.

The 10 year study found that of the 1,000 wild oat samples examined, herbicide Group 1 resistance was present in 68 percent and five percent also had Group 2 resistance. Group 8 resistance is also showing up prairie wide.

Other than tillage and adding a forage to the crop rotation, rotating herbicides and using herbicides with multiple modes of action are needed to avoid and correct for resistant pest plants, say agronomists.

Wild oat seeds persist in the soil for up to a decade, but 85 to 95 percent germinate in the first two years. Warm, dry fall seasons will promote dormancy in the seed. Nitrates from urea applications in the spring can cause dormancy to end.

If the weed is one leaf stage ahead of a wheat crop, yields of can be reduced by 15 percent if there are 16 wild oats found per square metre. On a 40 bushel crop this would cut yields by about six bushels. If the weed is at the same stage as the crop it cuts yields by nine percent and if the weed is a leaf stage behind the crop, it results in a five percent drop. In flax, 10 per square meter can cut yields by up to 20 percent.

Wild oats often emerges along with the crop and if that crop is a cereal, it can limit herbicide choices.

Despite effective herbicide introductions in the 1970s and 1980s, the pest remains abundant. Canola and other herbicide tolerant crops are effective against the pest.

In broadleaf crops, there are several grassy weed herbicides that can be effective, but control often requires application at the right time in the weed’s development.

Finer patterned spray nozzles and higher water rates can improve efficacy of herbicide application when it comes to the pest.

In cereals there are several choices of herbicides and most are affective if the weed is caught early.

The seed can remain viable in the soil for as long as seven years, so tillage of mature plants isn’t recommended. Reduced tillage keeps wild oats seeds in the seed bank from germination and can significantly cut infestations.

Using bin-run seed can compound efforts to control the pest. Clean seed is critical to reducing the pest. Producers can delay seeding, providing time for them to catch wild oats with spring applications of herbicides like glyphosate, ahead of the crop. Harrowing too can be effective at killing newly sprouted oats.

Higher seeding rates of cropped cereals make fields less hospitable for wild oats, however the rapidly growing weed can often outpace its crop host. Targeted application of fertilizer in, or near seed rows keeps some of it away from wild oats and makes crops more competitive, squeezing out the weed.

Canola and other herbicide tolerant crops are effective against the pest.

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