Some Peace fields have 4-5 adults per sweep, prompting many farmers to spray at the bud stage. This is earlier than normally recommended, but with drought stress, canola may not be able to compensate for bud losses.
Scout for signs of damage. Look for penetration marks at the base of the bud where adult lygus bugs are present.
If damage is evident, use the sweep net to take a count. Lloyd Dosdall, entomologist at the University of Alberta, provides these guidelines:
—Sample when the temperature is above 20°C using a standard insect sweep net with a 38 cm diameter.
—Take 10, 180-degree sweeps through the bud area.
—Count adult lygus numbers per 10 sweeps.
—If the count is 15 adults and higher at 5 locations within the field, if canola is stressed by drought ,and if lygus are actively feeding on buds, spraying may help under the current hot and dry growing conditions.
Other factors to consider in the decision are:
—Is the profit potential of the crop sufficient given the moisture situation?
—The potential that other insects will be a concern later in the season. Multiple sprays in one season may not be economical.
Click here for an Alberta Agriculture factsheet on lygus bugs.