Thin canola stands mean less margin for error for flea beetles

The Prairie Pest Monitoring Network warns that farmers may want to spray once flea beetles start eating a quarter or more of cotyledon leaf space

The flea beetles are out, and Manitoba Agriculture is reminding farmers to keep economic thresholds in mind when scouting their canola.

Manitoba Agriculture oilseeds specialist Dane Froese says beetle management might need some adjusting, depending on crop emergence. At the same time, dry conditions have farmers casting a careful eye on stand numbers.

Froese had already reported seed burn on emerging cereals during a May 16 webinar. The province notes that dry conditions raise seed burn risk if hot bands are placed too close to the seed.

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Manitoba still had adequate soil moisture as the first canola crops went in during the first weeks of May. Soil was generally wet enough to germinate and the first roots were drilling down towards moisture, Froese said.

That said, he added, canola was looking more and more for rain or risked a thin crop breaking ground. Some rain fell days later, although western Manitoba typically lingered below five millimetres while central Manitoba saw the bulk of the moisture along the U.S. border.

A thinner stand may affect how producers boost both weed and insect control, Froese stressed, both because there is less margin for plant loss, as well as less density to fend off weed pressure.

“Re-evaluate your canola stands after emergence,” Froese said. “Know what you tried to put in and what actually came out of it. Use that number to figure out what your anticipated yield could be.

“Anything above four plants per square foot is still looking quite well, provided we get that moisture,” he added. “Reseeding at that point is not generally the best recommended strategy. Normally, an original canola stand will have better yield than a reseed, unless there are some extreme circumstances.”

The Prairie Pest Monitoring Network warns that farmers may want to reach for the spray once flea beetles start eating a quarter or more of cotyledon leaf space.

“Watch for shot-hole feeding in seedling canola but also watch the growing point and stems of seedlings,” the group warned, noting that both vulnerable parts of the seedling are at high risk of beetle damage.

The Canola Council of Canada also recommends that farmers hone their focus on flea beetles. It puts economic thresholds closer to 50 per cent of cotyledon area loss, although farmers should still reach for the spray at a quarter, it said. That “action threshold” reflects how quickly losses can mount from a quarter of cotyledon loss to the economic threshold, the council says.

Dry conditions have also created good conditions for the pests.

The council warns that beetles thrive in heat and dry, while canola growth is hindered by the same conditions.

That slow growth also reduces the period of protection from seed treatment, and measures to curb flea beetles might not be enough for canola to grow past the four-leaf stage when flea beetles become less of a threat.

In more optimistic news, the canola council said certain control measures, including neonicotinoids, also pack more punch in dry conditions.

About the author

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Alexis Stockford

Alexis Stockford is a journalist and photographer with the Manitoba Co-operator. She previously reported with the Morden Times and was news editor of  campus newspaper, The Omega, at Thompson Rivers University in Kamloops, BC. She grew up on a mixed farm near Miami, Man.

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