Carcamo: Validation of lygus and other insect pest thresholds in commercial farms throughout the Prairie Provinces
Date: February 2021
Term: 4 years
Status: Completed
Researcher(s): Héctor Cárcamo, Jennifer Otani, Neil Harker, Breanne Tidemann, Patty Reid, Tyler Wist and Meghan Vankosky, Agriculture and Agri-Food Canada; Alejandro Costamagna and Tharshi Nagalingam, University of Manitoba; John Gavloski, Manitoba Agriculture; Piratheepa Jegatheeswaran and Daniel Johnson, University of Lethbridge
SaskCanola Investment: $213,480
Total Project Cost: $426,960
Funding Partners: Alberta Canola Producers Commission
Project Summary
Lygus bugs are a sporadic pest of canola at the pod stage across parts of western Canada. In this four-year study, researchers were interested in validating the economic thresholds of lygus in commercial canola fields across western Canada. As a result of the study, researchers have developed a protocol and validation of a new threshold for lygus in canola of 2-3 lygus per sweep. The study also showed that lygus bugs no longer reach pest status in most regions of the Prairies: Manitoba, Saskatchewan and northern Alberta. The pest risk from lygus occurs mainly in a narrow corridor between Edmonton and Lethbridge towards the foothills. Newer hybrid shatter resistant cultivars are likely more tolerant to lygus damage.
Lygus bugs are a sporadic pest of canola at the pod stage from southwestern to north central Alberta (along highway 2). In the Peace Region of Northern Alberta, some growers are concerned that they pose a risk even at earlier bud and early flower stages. In Saskatchewan they are sometimes a concern in the Meadow Lake area in the northwest and also in southern Manitoba where the thresholds were originally developed. Insecticide spraying during late flower or early pod is becoming a common practice in some regions but there is no agreement on economic thresholds and limited data for the benefit of spraying at the mid pod stage.
In this four-year study, researchers were interested in validating the economic thresholds of lygus in commercial canola fields across western Canada. Past studies in Alberta support the traditional threshold of 1-2 per sweep. The objectives of this study were also to determine the impact of spraying for other pest insects that may reach nominal economic thresholds, such as flea beetles or cabbage seedpod weevils. Additional objectives were to document landscape features that can influence risk of lygus damage, and survey lygus bugs in canola and validate thresholds.
To validate lygus thresholds, large plots were established in farmers' fields in Saskatchewan, Alberta, and Manitoba in each year. The treatments included unsprayed check plots and plots sprayed with an insecticide (Matador@34 ml/ac), which was generally done by the farmers using a ground sprayer or less often with a spray plane. Lygus bug sweep sampling was done at the early pod stage prior to insecticide treatment and at the mid-maturity pod stage a week after the plots were sprayed. Researchers identified and counted lygus bugs and other key pests or natural enemies collected in the sweeps in the field plots after spraying. Crop yield was also measured at harvest.
From the study, researchers developed a protocol to validate thresholds for lygus bugs and flea beetles in commercial fields and validated a new threshold for lygus in canola. The threshold derived from a previous cage study of 2-3 lygus per sweep is recommended. Despite large variability at many levels (within a field, between fields and years), there was a general pattern that abundances below 2 lygus per sweep do not reduce yield. Although current canola cultivars also appear to tolerate lygus damage better than older cultivars, growers should use the recommended threshold for all fields. There were no significant yield losses observed in this study. Although logistics made it impossible to study interactions between pests, it is still useful to keep track of lygus bugs in fields where flea beetles, cabbage seedpod weevils or diamondback moth delay crop maturity.
The study also showed that lygus bugs no longer reach pest status in most regions of the Prairies: Manitoba, Saskatchewan and northern Alberta. The pest risk from lygus occurs mainly in a narrow corridor between Edmonton and Lethbridge towards the foothills. The main pest species of lygus are Lygus keltoni, with L. lineolaris more dominant in the more northern portion of this corridor. Newer hybrid shatter resistant cultivars are likely more tolerant to lygus damage. Researchers also found that regions with fewer canola fields could result in higher lygus pest abundance because they concentrate in the fewer fields. Previous cropping history in a landscape had no effect on lygus abundance, which is not surprising given the high dispersal ability of these bugs.
As a result of the study, growers, industry and researchers now have a protocol and validation of a new threshold for lygus in canola of 2-3 lygus per sweep. In the future, researchers plan to develop a factsheet for industry for lygus bugs.
Lygus keltoni (often reddish) and L. elisus (pale) are two common species of lygus bugs in southern Alberta. Credit: Dan Johnson.
Additional information from 2021 showed hot and dry conditions led to major outbreaks of lygus throughout the Prairies, but particularly between Airdrie and Red Deer. A field with a check strip near Airdrie had lygus abundance up to 150 per sweep (threshold is 3 per sweep). Yield reduction in a check strip was substantial: preliminary data analysis suggests around 3-6 bushels per acre. These yield reductions from lygus (and other insects) were exacerbated by heat and drought.
Acknowledgement:
This study was funded through the Canola Agronomic Research Program (CARP).