Larvae of pea leaf weevils feed on the nitrogen-fixing nodules on pea roots. High levels of such feeding inhibit the nitrogen-fixing ability of the plant, which can reduce yields if the soils are nitrogen deficient. The first record of pea leaf weevil in Alberta was in 1997, and it was first found in Saskatchewan in 2007. At the start of 2019, it had not been confirmed from Manitoba but had been detected in eastern Saskatchewan.
In fall of 2019, an agronomist from northwest Manitoba sent in four weevils collected in early September from pea stubble near Swan River. The agronomist commented that they are easy to find in harvested pea fields. The weevils were identified as pea leaf weevils. That is the first confirmation of pea leaf weevils in Manitoba.
Only field peas and faba beans are potentially at risk of damage from pea leaf weevil. Other crops in the bean family may be fed on by adults but do not suffer significant damage from larvae.
In 2020, we are trying to determine the range of pea leaf weevil within Manitoba. That will require us finding the adult weevils. Vigilant scouting in the western part of our province is necessary to identify and manage the pest.
They can be captured in pheromone-baited traps, or collected from plants they may be feeding on. Adult weevils chew the leaf margins, resulting in a characteristic notching along the leaf margins. Pea growers or those scouting pea crops who think they may have pea leaf weevil in their field are advised to contact John Gavloski, entomologist with Manitoba Agriculture, or a production specialist with Manitoba Pulse & Soybean Growers. That will assist us in tracking the distribution of pea leaf weevil in Manitoba.
In spring, adults fly in from overwintering sites (perennial legume crops) and lay eggs close to host plants (field peas and faba beans). Larvae cause economic damage by feeding on root nodules, resulting in poor plant growth. Adult weevils feed on leaves, but rarely cause economic damage. The characteristic leaf notching on leaf margins can be used to monitor pest presence (Figure 1). The best time to look for potential feeding damage is at the end of May to early June.
For more information regarding pea leaf weevil scouting methods, thresholds and management, see NDSU’s Integrated Pest Management of Pea Leaf Weevil factsheet.
For a video explaining the action thresholds of pea leaf weevil and how to scout for feeding damage, view Pulse School: Scouting the Elusive Pea Leaf Weevil.