This was the situation many Peace region canola growers faced in 2010. Lygus bug counts were up to 3 to 4 per bud cluster in severely drought-stressed fields. Growers were concerned their drought-stressed canola wouldn’t be able to compensate as it would under better growing conditions.

What should they do?

Scout for signs of damage. Overwintered adults, which have the “V” mark one third of the way down their backs, are doing most of the feeding at this stage. Feeding lygus bugs suck on the bud stem and the bud itself, causing bud abortion. Look for penetration marks at the base of the bud where lygus bugs are present. If damage is evident, get out the sweep net.

Guidelines for assessing lygus bug impact on canola at the bud stage:

• 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 at this threshold.

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.

At this stage of the canola crop, we can assume that most adult lygus bugs have not arrived and diamondback moth larvae are not present yet either. A grower has to ask how many insecticide sprays are economical given the lower yield potential of a drought-stressed crop.

Also, spraying now to reduce lygus numbers will not eliminate the lygus threat at flower and pod stages. Lygus are very mobile and will move in from other areas.

If the grower does decide to spray, check the provincial guide to crop protection for products registered for lygus bug as well as application tips and timing. Click your province for a link to the guide: Alberta Saskatchewan Manitoba. You can also click here for an Alberta Agriculture factsheet on lygus bugs.

Published on Tuesday, June 29, 2010