Pea Leaf Weevil Threat Expands

EDMONTON - Dec 11/17 - SNS --┬ĘDamage from pea leaf weevil on field peas and fababeans grown in Alberta was less in 2017 than the previous year, but the area covered by the insects is expanding.

Overall the severity of pea leaf weevil feeding damage was slightly lower compared to 2016. The most obvious reduction in adult damage by pea leaf weevil was Wheatland and Kneehill counties east to the Saskatchewan border in south-central Alberta. Adult damage was slightly lower in Lethbridge county but east towards Medicine Hat was higher than in 2016.

Pea leaf weevil is now established from southern Alberta through west-central Alberta as far as Barrhead County northwest of Edmonton. Parkland, Lac Ste. Anne, Westlock and Barrhead counties all experienced higher pea leaf adult feeding than in 2016. Sturgeon and Strathcona counties were similar to slightly higher than 2016 but Lamont county still remains relatively low in pea leaf weevil activity.

The survey also shows that pea leaf weevil is now found in all counties to the east of Edmonton including Bonnyville and St. Paul. The survey was also expanded into the Peace region including Greenview, Smoky River and Big Lakes with very low levels of feeding notches found in all three areas. The presence of the weevil in the Peace Region was confirmed later in the season by researchers from the University of Alberta.

While this is not a strict forecast, experience has shown us that activity levels greater than 9 notches per plant is sufficient to cause significant damage if conditions are favorable in the spring of 2018. This covers a large area of southern and west central Alberta. For any producers south of Highway 9 and along Highway 2 up to Edmonton there is a risk of damaging levels of pea leaf weevil in 2018. Producers should use this information along with their own experience to plan control strategies such as seed treatment for the 2018 crop year. Research has shown that seed treatment is much more effective in reducing losses from pea leaf weevil than foliar treatments.

In addition, since 2014 significant pea leaf weevil damage has been seen on fababeans in a much larger area than shown in this survey that is conducted on field peas. This insect causes as much or more damage on fababeans. The true economic damage of this insect on both peas and fababeans on the higher organic matter soils of central Alberta is not well understood but research has been initiated to work out these relationships.

Based on studies of pea leaf weevil biology, moisture in August appears to be a significant predictor of increases in the population. Together this information suggests that pea leaf weevil has the potential to be a very important pest in 2018.

Spring weather conditions have a very large impact on the timing and severity of pea leaf weevil damage. When warm conditions (>20 C) persist for more than a few days in late April or early May the weevils arrive in fields early. Early arrival corresponds to the potential for higher yield losses. In years where cool weather persists, the arrival of PLW can be much later and the resulting yield impact appears to be lower especially when the crop advances past the 6 node stage before weevils arrive. In every case control decisions should be made on a field by field basis.