Diamondback moth larvae have become a growing concern in canola this year.

Brittany Hennig, Agronomy Specialist for Southern Alberta with the Canola Council of Canada, says the numbers have come as a bit of a shock to them this year.

"We had traps set up across the prairies, and we didn't see any numbers that were overly concerning. This is an atypical year, not very common. A lot of the research done on the diamond back is older, so we need to do a little bit more research on them, and assess why the population increased this year."

They are identified by their particular reaction to being disturbed. The larvae will violently move back and forth, and may drop from the plant suspended by a silky thread.

Hennig says regions in the Central and Northern Areas of the province seem to be doing ok since their plants have been doing well with the moisture, and have more substance to them.

Meanwhile, it's a different story for canola growers in Southern Alberta.

"In the South, where it's really dry, there aren't those bottom leaves on the plant anymore, so they are moving straight for the top of the plant and out to the pods."

To do a count in your field, she says you can't sweep the larvae. Instead, pull the plant out of the ground and knock it on the hood of your truck to do a count. Then, multiply the total by the number of plants you have per square foot, and convert to meters squared.

Threshold is 200-300 larvae per meter squared, and many areas in Southern Alberta have passed these levels.

Even 150 larvae per square meter could look like a lot, but it's important to physically count them to determine if it's worth spraying at a cost of about $15 to $25 per acre.

Hennig says, if you do have to spray, be certain to leave the right pre-harvest interval.