Faba Beans, FP Insects

Pea Leaf Weevil – A New Pest in Manitoba

In spring, pea leaf weevil adults fly in from overwintering sites (perennial legume crops) and lay eggs near field pea and faba bean host plants. Larvae cause economic damage by feeding on root nodules, resulting in poor plant growth and reduced nitrogen fixation. Adult weevils feed above ground on leaves, but rarely cause economic damage. The characteristic leaf notching on leaf margins can be used to monitor adult weevil presence (Figure 1). The best time to look for potential feeding damage is at the end of May to early June when peas and faba beans are emerging up to V5 (fifth node stage).

Leaf notching on lower leaves from adult pea leaf weevil feeding.

The first record of pea leaf weevil in Alberta was in 1997, and it was first found in Saskatchewan in 2007. In the fall of 2019, it’s presence was confirmed in northwest Manitoba near Swan River.

Adult pea leaf weevil showing alternating light and dark brown stripes extending from the thorax to the abdomen Photo: H. Goulet, AAFC-Ottawa.

Since then it has been confirmed near Gilbert Plains, Dauphin and, in the spring of 2021, near Plumas as well.

Only field peas and faba beans are at risk of damage from pea leaf weevil. Other crops in the legume family (soybeans, dry beans) may be fed on by adults but do not suffer significant damage from larvae.

In 2021, 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.

Pea leaf weevils 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.

Management

In field peas, economic thresholds for foliar insecticide applications are once 30% of plants have notches on the uppermost closed stipule or clam leaf at V2 – V3 (two to three true nodes). However, insecticide applications do not prevent yield loss since healthy adult weevils will continue to travel into the field from elsewhere and, if there are notches on the expanded leaves below the clam leaves, female weevils have likely already laid eggs in the field.

Seed treatments are a more effective option. Seed treatments containing imidacloprid and thiamethoxam offer protection against the pea leaf weevil. However, populations of pea leaf weevil are very low in Manitoba and seed treatments are unlikely to provide a return on investment at current population levels.

Ground beetles and rove beetles are predators of pea leaf weevil, eating eggs on the soil surface.

Cultural control methods are being investigated. Reduced tillage systems, trap cropping, and intercropping are options to reduce the impact of pea leaf weevil. Factors that promote rapid crop establishment also produces more resilient plants.