Estimating the Abundance of Lygus in Canola Fields

Date: December 1995
Term: 1 year
Status: Completed
Researcher: R. Lamb, Agriculture & Agri-Food Canada
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Lygus bugs can be important pests of canola in western Canada. At the time of this study in 1994, researchers had developed control strategies, but lacked an efficient sampling method. Researchers from Agriculture and Agri-Food Canada, Winnipeg conducted a one-year study to evaluate various sampling methods to determine lygus bug infestation levels. As a result, researchers developed an efficient sweep sample method that allows producers to efficiently assess the risk of lygus damage and minimize yield loss and control costs, resulting in yield savings of up to about 20% in some fields.

Lygus bugs can be important pests of canola in western Canada. They feed on the growing points of canola plants and can cause damage to canola, particularly when they attack pods and feed directly on developing seeds. This damage is usually invisible, but may result in a lower than expected yield. Sampling and estimating economic thresholds were a challenge.

Although an economic threshold and control strategy had been developed for these pests, an efficient sampling scheme was required for producers to use the control strategy effectively. Researchers from the Agriculture and Agri-Food Canada, Winnipeg conducted a one-year study in 1994 to evaluate various sampling methods to determine lygus bug infestation levels. The sampling methods were tested in a large experimental plot at Glenlea, Manitoba and in 15 commercial fields in Manitoba.

The objectives of the study were to determine where lygus bugs occur on canola plants at various stages of growth and to determine whether lygus bugs were evenly distributed in the field. Researchers also wanted to compare the efficiency and accuracy of four sampling methods: vacuum, sweep net, beating tray and absolute counts. Researchers also wanted to devise an efficient method for producers or pesticide applicators to estimate lygus abundance in canola and determine whether control was necessary. They also wanted to devise a precise method for researchers to estimate abundance and sample lygus in experimental plots.

As a result of the study, researchers developed a successful sampling method for producers. A sweep net proved to be the most effective sampling tool. Sweep sampling also collected about one-half of the lygus present in the sampled area and the age distribution of the lygus were similar in the sweep samples and absolute counts. Lygus bugs were relatively evenly distributed in canola fields so that their densities could be estimated at the edges of the fields.

The research showed that to determine whether or not lygus densities had exceeded the economic threshold of about 1.5 lygus bugs per sweep, producers needed to use a sweep net to sample the edges of their fields when the crop had almost finished blooming. Researchers estimated that up to 12 twenty-sweep samples were required per field for an accurate estimate, less if infestations were lower. A single sample of twenty-sweeps could be completed in about 2 minutes so that sampling a field to make a control decision could be completed in 30 to 45 minutes. This method allows producers to efficiently assess the risk of lygus damage and minimize yield loss and control costs. This method could result in yield savings of up to about 20% in some fields.

Scientific Publications

Wise, I.L., and R.J. Lamb. 1998. Sampling plant bugs, Lygus spp. (Heteroptera: Miridae), in canola to make control decisions. The Canadian Entomologist 130: 837-851.

Full Report PDF: Estimating the Abundance of Lygus in Canola Fields