With this insect’s range expanding, and few current tools working well, new research is considering cultural and biological control methods.

Let’s say you grew a high-yielding cereal crop one year. By planting time the following year, a soil test illustrates the field is relatively nitrogen poor. That’s okay, because you’re growing peas next.

However, if pea leaf weevils are present that spring, this low soil nitrogen could cause big headaches down the road. Field Crop Entomologist Meghan Vankosky explains that bacteria in a pulse crop’s root nodules fix nitrogen that can be used by the plant to produce yield and to improve soil nitrogen reserves. Since pea leaf weevil larvae feed on those nodules, they impair the plant’s ability to fix nitrogen.

“There’s real concern for potential yield loss due to pea leaf weevil if you’re planting peas into low nitrogen soil, which is what we like to do,” said Vankosky, Research Scientist with Agriculture and Agri-Food Canada.

Currently, only one foliar insecticide is registered for pea leaf weevil. Insecticide seed treatment can work but must be purchased long before there’s evidence of a pea leaf weevil infestation.

“For growers in areas with high pea leaf weevil pressure, the recommendation tends to be insecticide seed treatment,” said Vankosky. “Outside those areas, it’s a gamble for producers to treat seeds but if weevils show up in big numbers, the foliar spray isn’t very effective either.”

In 2018, Vankosky began a three-year research project to study Integrated Pest Management (IPM) for pea leaf weevil in pea and faba bean crops with funding from the Canadian Pulse Science Research Cluster. The project will examine three potential ways to manage pea leaf weevil with less environmental impact.

1. Beneficial insects. “We know there are potential natural enemies of this pest, but the current research barely scratches the surface,” said Vankosky. “We want to figure out the species here on the Canadian Prairies that might eat pea leaf weevil and the impact of that.”

 

2. Trap crops. Another strategy that will be tested is the planting of trap strips in July. When the new generation of pea leaf weevil feed on the trap crops in the fall, researchers will test alternative control methods to determine if it is feasible to control pest populations in the fall.

 

3. Pheromone traps. Using a pheromone-baited pitfall trap developed by University of Alberta Entomologist Maya Evenden, Vankosky is testing whether this system could be part of a trap-and-kill strategy to manage pea leaf weevil populations. An agent as mild as soapy water could be enough to kill trapped weevils.

With research showing a vigorous pea leaf weevil spread in Alberta over the last few years, Vankosky wants to give growers options beyond the current limited toolbox.

“The idea is to reduce the number of weevils overwintering or going into the fields in the spring,” Vankosky said. “We need to quantify the efficacy of these ideas. We’re not recommending anything to farmers without first testing those ideas ourselves.”