Weed of the Week: wild oats

They are everywhere, and in some cases they are getting hard to kill.

Wild oats, formally known as avena fatua, cost farmers an estimated $500 million dollars a year, and despite a wide range of tools to control the pest, some of the best are the old-school ones.

Despite being a problem for most of the past 100 years, prairie producers are still losing yield and spending more on controlling the weed than ever. Due to herbicide resistance, prairie farmers’ fight with the pest isn’t likely to end any time soon.

Hugh Beckie of Agriculture Canada’s research centre in Saskatoon has said wild oats remain among the 10 worst annual weeds that cereal producers must contend with worldwide.

More than 10 million acres in Western Canada are affected by herbicide resistant weeds, and most of those incidents are wild oats.

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

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

Over half of the cultivated fields in Alberta have Group 1 resistant wild oats. Group 1 resistant wild oats were found in 11 percent of fields in 2001, rising to 30 percent in 2007 and more than 50 percent by 2015, according to Agriculture Canada researcher Neil Harker in Lacombe, Alta.

Reduced tillage and continuous cropping have aided wild oats. Flooding that allows weeds to reach seed maturity have created other problems. The need for chemical control in place of steel and diesel fuel has selected for resistant genetics in wild oats, especially for those herbicides with a single mode of action.

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.

Yields can be reduced by 15 percent if the weed is present at the one leaf stage ahead of a wheat crop and 16 wild oats are found per sq. metre. This would cut yields by about six bushels on a 40 bu. crop.

Yields drop by nine percent in wheat if the weed is at the same stage as the crop and by five percent if the weed is a leaf stage behind the crop.

In flax, 10 weeds per sq. metre can cut yields by up to 20 percent.

Wild oats often emerge along with the crop, which can limit herbicide choices if the crop is a cereal.

The pest remains abundant despite effective herbicide options introduced in the 1970s and 1980s. Canola and other herbicide tolerant crops are effective against the weed.

Several grassy weed herbicides can be effective in broadleaf crops, but control often requires application at the right time in the weed’s development.

Reduced tillage can control germination and significantly cut infestations. Diverse crop rotations are beneficial.

Producers can delay seeding, providing time to catch wild oats with spring applications of herbicides such as glyphosate ahead of the crop. Harrowing can also kill newly sprouted oats, which are more susceptible to light tillage than wheat.

Higher seeding rates of cropped cereals make fields less hospitable for wild oats, but the rapidly growing weed can often outpace its crop host.

Avadex, a soil applied Group 8 herbicide, has been used for decades to control the pest, but its separate application and moderate cost encourage some producers to use the option sparingly.

Harker said producers should avoid becoming too dependent on it because of resistance concerns.

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