This is not a forecast. It is a summary of the pea leaf weevil situation in Alberta in spring 2024.
Methodology
The pea leaf weevil (Sitona lineatus) survey was completed in late May and early June 2024. It is based on damage ratings in 219 fields from 56 municipalities.
In each field, the total number of feeding notches per plant are counted on 10 plants in 5 locations near the field edge for a total of 50 plants. The damage rating for a particular field is the average number of notches per plant. This survey concentrates on damage done by the adult, yield losses are caused by the larval damage to the nitrogen fixing root nodules.
2024 survey findings
The circles on the map show the general area where the monitoring took place. There was a reduction in the notches per plant when compared to 2023. The area affected by weevil feeding shifted from the eastern part of the province (2023), to along the Highway 2 corridor from Olds to Thorhild. Weevil damage remains low in the southern region, although we can find hotspots in the survey.
We do know that pea leaf weevil is in the Peace region, but the 2024 survey technicians could find very little feeding damage in any of the fields surveyed. There are other weevil species in the Peace with similar feeding damage on the leaves of peas.
Producers should use the information generated from this survey, along with their own experience to plan control strategies such as seed treatment for the 2024 crop year. Research has shown that seed treatment is much more effective in reducing losses from pea leaf weevil than foliar treatments. The economic threshold for pea leaf weevil is 30% of the seedings with clam leaf (terminal leaf) damage during the second to fifth node stage. This is meant to indicate larval pressure, seedlings will recover from feeding damage, except in very severe cases.
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 20C) 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 6-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 faba beans 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 faba beans. The true economic damage of pea leaf weevil on both peas and faba beans on the higher organic matter soils is not well understood, but research has been started understand this relationship.
Find out more about the pea leaf weevil life cycle.
Acknowledgements
Thanks to Remy Strach and Alberta Plant Health Lab Survey Technicians for their contribution to the survey. Thanks to Jon Williams, AAFC-Saskatoon, for building the map.