Pea leaf weevils are out and active, and if they’re present in your fields they’re doing foliar damage to pea and faba bean crops.
Meghan Vankosky, field crop entomologist at Agriculture and Agri-Food Canada, Saskatoon, Sask., joins Kara Oosterhuis for a discussion about pea leaf weevil scouting and thresholds in this Pulse School episode.
“You want to get out when the plants are at the two to six node stage, really before root nodules are starting to form,” says Vankosky.
To determine the damage level, Vankosky says that a nominal threshold is used for pea leaf weevil. If more than 30 per cent of plants have damage on the terminal, or clam leaves, the threshold for considering a foliar spray is met.
“The only issue is that all of the research that we’ve done and not yet published has shown that using foliar sprays really isn’t effective against pea leaf weevil,” says Vanksosky, adding that the pest insect disperses over long periods of time, and the residual time of a foliar spray isn’t long enough.
Adult weevils are three to four millimetres long, brownish grey in colour, with stripes down their backs. Pea leaf weevil is different from other weevils, in that they have short, broad noses instead of long noses. Damage to the plant is very characteristic U-shaped notches to peas or faba beans, but they will also attack alfalfa or sweet clover.
Catch the full conversation for more on pea leaf weevil life cycle and this year’s population distribution:
Vankosky, and others, are currently researching whether or not carabid, or ground, beetles have any effect on pea leaf weevil populations, which could potentially eat the larvae of pea leaf weevil that would normally emerge from root nodules.
Damage levels to the crop are variable, according to previous research, and also according to soil properties.
“If you’re planting your peas into pretty rich soil, with lots of nitrogen, then the impact of the larval feeding can be reduced, so there might not be a huge yield impact,” says Vankosky, “But, if you have a really weevil population at the right time of year, you can see seedlings dying because of the foliar damage, and then later on we’ll see that there’s so many weevils, in terms of adults and larvae, that it can be overwhelming for the plant.”
Vankosky suggests that if the populations are high enough, to use an insecticidal seed treatment at seeding to try to reduce risk as the season goes on. The Prairie Pest Monitoring risk maps from the previous winter will indicate if populations will be high.