Wheat School: Toppled stems indicate wheat stem sawfly


Wheat stem sawfly is thought to be native to parts of the southern Prairie provinces, and forecasting maps show that the pest is certainly present this year.

“This is the time of the year where we’re starting to see some of those wheat stems topple over from wheat stem sawfly,” says Jeremy Boychyn, agronomy research extension specialist at Alberta Wheat and Barley Commissions. “Wheat stem sawfly is a pest that comes in on wheat, and we’ve seen, based on forecasts, that it has a lot of presence in the southern part of the province.”

The pest chews into the wheat stem, tunnels down the stem of the plant, and at the end of the season will cut a small notch in the bottom of the stem as they exit, which causes the plant to topple over.

Typically, there’s higher pressure from this pest insect around field edges, says Boychyn, but he recommends to go out and scout the whole field to determine what kind of pressure the crop is under, and where.

Watch the full video for tips on how to scout for wheat stem sawfly, story continues below:

“If you’re at zero to two stems, per 10 stems, you’re at very low pressure, if you’re at two to four, then you’re at moderate pressure, if you’re four plus, per 10 stems, then you’re in the higher pressure area,” says Boychyn, adding a general recommendation that if 15 per cent of stems are affected, to use a solid-stemmed wheat variety or durum variety for the following year.

There is a beneficial insect to consider that attacks wheat stem sawfly, called Bracon cephi, that lives just above wheat stem sawfly. Cutting height at harvest, above approximately 15 cm (six inches) will maintain that beneficial insect in the crop.

Before seeding next year, more aggressive or doing two passes at harrowing might also control wheat stem sawfly, says Boychyn.

Depending on the pressure of wheat stem sawfly, Boychyn also recommends to swath the outside rounds, or the whole field, so that quality and yield are maintained.

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