This is not a forecast. It is a summary of the pea leaf weevil situation in Alberta in spring 2020.

Methodology

The annual pea leaf weevil (Sitona lineatus L.) survey was completed in late May and early June 2020. It was based on damage ratings in 237 fields from 58 municipalities.

In each field, the total number of feeding notches per plant are counted on 10 plants in 5 locations near the field margin. The damage rating for a particular field is the average number of notches per plant. Although this survey concentrates on damage done by the adult, yield losses are caused by the larval damage to the nitrogen fixing root nodules.

Survey findings

The highest damage ratings were around Edmonton. The population in southern Alberta remains at levels that could cause concern in random areas in 2021. Numbers remain low in the Peace region, and pea leaf weevil is now established from southern Alberta through to the Peace. Survey locations shown with black circles had no evidence of pea leaf weevil feeding on any of the plants assessed.

This survey covers the irrigated area of southern Alberta and the region around Edmonton. For producers in these higher areas in 2020, there is a risk of damaging levels of pea leaf weevil in 2021. Producers should use this information along with their own experience to plan control strategies such as seed treatment for the 2021 crop year. Research has shown that seed treatment is much more effective in reducing losses from pea leaf weevil than foliar treatments.

Spring weather conditions

Spring weather conditions have a very large impact on the timing and severity of pea leaf weevil damage. When warm conditions (greater than 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, PLW’s arrival can be much later and the resulting yield impact is lower especially when the crop advances past the six-node stage before weevils arrive. In every case, control decisions should be made on a field-by-field basis.

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 pea leaf weevil 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.

Acknowledgements

Thank you to Janet Lepp, Alberta Agriculture and Forestry for managing the data. Thank you to Raquel Neeser-Carazo and Brennan Folkerts for your contribution to the survey. Thank you also to David Giffen, Agriculture and Agri-Food Canada, Saskatoon for building the map.

Resources

Pea Leaf Weevil factsheet

Historical pea leaf weevil population maps