We are about two weeks away from looking at bugs in canola. There are three bugs that need to watched. They are diamond back moths, bertha army worms, and lygus bugs. All these bugs have potential to cause yield loss and need to be monitored so that the timing of control is what it needs to be to get the proper control. Lygus bugs will be the first insect to show up. It is an insect that sucks the juice out of the tissues of a canola plant. The yield loss potential becomes high when the bugs move onto the pods. Every place where the insect sucks the juice out of the pods, the seed below the area will be dead. A sweep net is required to look for these insects. With the sweep net counts, the economics of spraying can be determined. Find someone with experience to show you how to use a sweep net properly to figure out if you are using the right economic thresholds. With diamond back moths, it is the larva that do the damage on canola plants rather than the adult insects. The damage is similar to the lygus bug injury. Damage on the pods will kill the seed under the affected spot. Again, the only damage that is important with these insects is when the suck the juices out of the pods. A heavy rain can wash off the bugs. If the bugs show up late when the pods have hardened up, the damage will be reduced. Once the flowers and green leaves disappear, all the larvae move onto the pods and damage will increase. Samples from a specified area must be taken and the plants need to be banged hard against something to get accurate counts. Make sure the counts are accurate by comparing them to someone with experience at counting. The damage from bertha armyworms will be the last insect that could show up in your field this season. The larvae of this insect chews on the pods and whatever is chewed on is lost. To check for these insects, take a scoop shovel and place it under the canopy of the crop. Tap the crop and count the number of insects that fall into the scoop shovel. This will give an indication if the field is worth spraying. With any insect, it is essential to know the economic threshold for the specific insect. It gets more complicated when all three of the insects are present in a field. The thresholds will be low this season because the price of canola is high and therefore the amount of canola required to pay for the spraying is small. With any control practice applied in your fields, be sure that the control measure makes economic sense. Get out early and look for damage. If the damage is there, figure out what the economic threshold for the insect is and spray if you need to. If you are going to spray, contact your local honey bee operator to be sure you do not damage his bees.
By Dave Cubbon, P Ag