Peace canola may need early lygus spray

Tuesday, June 29, 2010

Lygus bug feeding on canola at the bud stage is not normally cause for concern. Canola will generally outgrow damage by flowering longer and putting out more buds to compensate. But canola under drought stress may not be able to compensate for buds lost to lygus feeding.

“ We are getting reports of up to 3-4 lygus bugs per bud cluster in some areas of the Peace River region, where canola is under drought stress this year,” says Erin Brock, Canola Council of Canada agronomist. Growers are concerned their drought-stressed canola won’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 lygus are actively feeding on buds, spraying may help at this threshold.
These guidelines were prepared by Lloyd Dosdall, entomologist at the University of Alberta.
 
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.

Most adult lygus bugs have not arrived, and with diamondback moth larvae showing up, a grower has to ask how many insecticide sprays are economical given the lower yield potential of a drought-stressed crop. Some growers have already sprayed for cutworms this season.

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.

Jennifer Otani, insect pest management biologist with AAFC in Beaverlodge, Alta., would wait a few days before spraying. “If a healthy stand at the bud stage fails to flower within the next 4-5 days, I'd be out sweeping to see what numbers are there for lygus bugs plus diamondback larvae,” Otani says. “If numbers are within economic thresholds for that crop stage, I'd consider an insecticide spray.”

Make sure the proper insecticide is used for the pest. Check your 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.

 

 

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