Previous research has indicated that preventative insecticide seed treatments are a more effective option to managing PLW. However, it is uncertain at what PLW population level we can expect to see a return on investment to using an insecticide seed treatment in peas. The goal of this research commissioned by Manitoba Pulse & Soybean Growers is to compare existing registered insecticide pea seed treatments for PLW control (Table 1) and to compare results with PLW population pressure to determine when we may see a return on investment to these products.
Table 1. Available registered seed treatments for pea leaf weevil control in peas.
Year 1 and 2 Results and continued study in 2025
In 2023 and 2024, small-plot trials were established at Roblin with PCDF and Swan River with New Era Ag comparing untreated peas to peas treated with Cruiser 5FS (thiamethoxam), Stress Shield 600 (imidacloprid) or Lumivia CPL (chlorantraniliprole). One field-scale on-farm trial was also established each year through MPSG’s On-Farm Network. In 2023, near Roblin a farmer compared untreated peas to those treated with imidacloprid and Rancona trio (a fungicide seed treatment). In 2024, an on-farm trial near Minitonas compared untreated peas to those treated with Cruiser (thiamethoxam) and Vibrance Max (fungicide seed treatment).
Results presented here are preliminary and these trials are planned to continue for another year.
At V6, total leaf notches per plant were counted on 10 plants in each plot to provide an indication of pea leaf weevil predation and population (Figure 4). There were no differences in PLW predation among seed treatments and the untreated check at Roblin or at the on-farm trial in 2023. At Swan River in 2023, PLW predation was reduced with Cruiser (thiamethoxam) seed treatment compared to untreated peas.
Within each site-year, bars followed by different letters are significantly different at p <0.05.
In 2024, total leaf notches per plant were recorded at V9 in Roblin, at V6 and R1 in Swan River and at V6 at the on-farm trial near Minitonas. There were no significant difference among treatments regarding PLW feeding damage in 2024.
Within each site-year, bars followed by different letters are significantly different at p <0.05.
There were no statistically significant yield differences among pea seed treatments and the untreated check at either Roblin or Swan River in 2023 or 2024. Yields were poor at Roblin in 2023 due to late seeding into dry soils followed by challenging growing season conditions.
Within each site-year, bars followed by different letters are significantly different at p <0.05.
Within each site-year, bars followed by different letters are significantly different at p <0.05.
These results are preliminary. There was a trend of reduced PLW predation with Cruiser (thiamethoxam) and Stress Shield (imidacloprid) seed treatments, but this did not translate to any yield improvements. PLW populations may be so great in these areas that any seed treatment effects are masked by excessive pest pressure.
Small-plot trials have continued for 2025 at Roblin (PCDF), Swan River (New Era Ag) and Melita (WADO).
Our MPSG scouting network also takes 2025 PWL counts in commercial pea and faba bean fields.
Pea leaf weevils also nibble on faba bean leaves
