Knowing the distribution and severity of this invasive insect would allow growers to make better management decisions and use insecticide only when needed.

How bad will pea leaf weevil be in your 2019 field pea crop? It’s a question that’s hard for growers to answer. First, you need to know whether pea leaf weevil is in the neighborhood. Second, since this pest is only an intermittent problem, you need to know whether an infestation is likely to be mild, medium or severe.

University of Alberta entomologist Maya Evenden developed a pea leaf weevil monitoring trap to help provide these insights.

“The only way we can find pea leaf weevils when they are still at low densities is by using these traps,” Evenden said. “The feeding damage is really hard to find when weevil populations are at low densities. Putting out these traps lets us know where the leading edge of expansion is because the tool monitors low densities of pea leaf weevil.”

Although pea leaf weevil has been mainly a southern Alberta problem, over the past several years, the pest caused considerable damage in Central Alberta and was found in the Peace region for the first time in 2018.

Between 2014 and 2017, Evenden and her team tested different lures and trap designs and landed on what she considered the best design: a basic pitfall trap. To catch the rice-sized adult pea leaf weevils, a cup is dug into the ground and a pheromone lure hangs from the cup’s small roof. A mesh over the mouth of the cup helps avoid capture of non-target organisms.

Trapping this pest is about placement and timing

Now, with two years of new funding from Alberta Pulse Growers and others in place, Evenden’s expanding her work. In Spring 2018, she and her team distributed pea leaf weevil pitfall traps in newly-seeded Alberta pea and faba bean fields. Knowing there is already a problem in the south, Evenden selected trap sites in the north, northeast and northwest parts of the province.

“There are two times of year we can trap pea leaf weevils,” Evenden said. “One is when they move into the fields in the spring, and the other is in the fall when they are moving out of the field to overwinter.”

Evenden hopes to use the spring catch information to compare numbers with adult weevil feeding activity and damage seen in the crops. For the fall trapping, where catch numbers are typically much higher, the data can help her estimate pea leaf weevil numbers the following spring.

Pea leaf weevil monitoring will help map the range of this pest in Alberta and tell pea and faba bean growers how likely it is that the pest will be a problem over the coming year. This would be a key insight for deciding whether or not spring seed treatment is needed.

“When we found them in the Peace, I was disappointed for growers, but the fact that we detected them at such a low level meant our monitoring is working,” Evenden said. “It would be great to be able to disseminate this kind of information to growers ahead of time. The research has also indicated that we might be on the verge of developing tools that use pheromone cues in control. It’s a big contribution.”