In recent years, high populations of lygus bugs have been reported in a large portion of Alberta, as well as in some fields in Saskatchewan and Manitoba. While lygus bugs are always present in canola fields, outbreaks of high populations can cause extensive crop damage.
For the most part, canola can compensate for much of the damage caused, but sometimes it cannot. In 1997, crop damage to canola in Alberta exceeded $10 million. More than 1.4 million acres were sprayed to control lygus bugs. Outbreaks were fairly isolated until about 2012, when high populations were reported across the Prairies.
Lygus bugs are small, oval-shaped insects that feed on a variety of crops, including canola, alfalfa, lentils, flax and hemp. They also feed on many weeds, including flixweed, lamb’s quarters, stinkweed and hoary cress.
Depending on their geographical location, lygus bugs have up to three generations per year. Should a late fall or early spring occur, an additional generation is possible. Species vary from province to province, too. In Alberta, for instance, growers see more Lygus keltoni, whereas Manitoba growers see more Lygus lineolaris.
Lygus bugs are about three mm wide and six mm long. The have a fairly long antennae and their coloration ranges from pale green to reddish brown to black. Identification is made easy by a very distinctive V-shaped marking, located in the upper centre of their backs. Adult lygus bugs are very active and will fly away when approached.
- From the Manitoba Co-operator: Pest surveillance branch update, June 19
Overwintering in places where they can find shelter under plant litter, lygus bugs emerge in late spring and begin to reproduce on early season hosts, like alfalfa.
Managing for lygus bugs
There have never really been any serious outbreaks in Manitoba — not like the ones in Alberta — but they still require management, says John Gavloski, entomologist with Manitoba Agriculture, Food and Rural Development. “But we certainly have had years where lygus bug has been an economic problem in canola.”
The first step in managing the pest is regular scouting. Monitor fields closely, especially in areas where overwintering populations may be high. Since the oldest bugs are responsible for the most damage, it’s important to not only count numbers, but also to determine what part of the life cycle the majority are in. Lygus bugs go through several nit stages, and eventually molt into the adult, says Gavloski. “As they get bigger, they’re progressively taking more of the sap per individual. They do move around when they’re young. They’re very mobile insects to begin with. But as they get bigger, they ingest more.”
The best method for scouting is sweep net monitoring, which should be done under the right weather conditions (sunny, low wind, above 15 C and between the hours of 10 a.m. and 4 p.m.). Be sure to sample several areas in the field.
“Best to start sweeping either late-bud or as we get into the early-flowering stages,” says Gavloski.
The problem with scouting for lygus bugs is that they’re fast, he says. “Even if there are a lot of them there, you won’t see too many because they’re very quick and they’re hard to see on the plant.”
Thresholds are based on sweep net sampling. Because they move so quickly, counting lygus bugs in a sweep net can be difficult. Be sure to sweep in several locations. To obtain more accurate counts, slowly invert the net allowing one bug to escape at a time. Either that, or invert the net into a Ziploc bag and carefully count each insect through the plastic.
Some of the newer canola varieties grow exceptionally tall. They can be denser and harder to walk through, which makes sweep netting a challenge. In these types of crops, it is perfectly acceptable to sweep along the crop’s edges, says Gavloski, but only if the crop is at the same growth stage as the rest of the field.
To determine if populations are in excess of economic thresholds, use the charts below, taking into consideration application costs, canola prices and plant development stage.