By: John Ippolito, PAg, Regional Crop Specialist, Kindersley
Pea leaf weevil were first identified as being present in Saskatchewan in 2007. Since that time, there has been an annual survey conducted to determine the geographic area that has the pea leaf weevil present.
In the past few years, the area of infestation in Saskatchewan has increased in size as they have moved further east and also north across the South Saskatchewan River.
Pea leaf weevil adults emerge in mid to late May and feed on the leaves of field peas. Adults are nocturnal and are in cracks in the soil during the day, so they may not be noticed. Their presence can be identified by the notches in the leaf margins as a result of feeding. After feeding for a period, eggs are laid at the base of the plants and larvae emerge within a few weeks. Economic losses are most often associated with the larvae feeding. The larvae feed on the nitrogen fixing nodules and roots of the plant and reduce yield through reduced nitrogen fixation and uptake. This feeding can occur for as long as 6 weeks.
Scouting for injury from the pea leaf weevil should occur from the two to five node stage. The clam leaves should be examined for damage in the form of notches. Damage will be most prevalent along field edges, but at least five locations at least 100 metres into the field should be inspected. Insecticide control may be warranted if there is feeding damage to 30 per cent of the clam leaves inspected. Damage to earlier leaves is an indicator that the feeding may have already stopped and the insecticide will not be effective.
The most effective control for pea leaf weevil is to use a seed treatment with an insecticide component at the time of seeding. This will control larvae feeding which has the largest impact. Scouting this year for above ground feeding may provide valuable information regarding the presence of pea leaf weevil and assist in decision making regarding the use of seed treatment when planting field peas in the future.
More information on the pea leaf weevil can be found on the Prairie Pest Monitoring Network blog.