Count larvae by taking whole plants and knocking on the hood of a car or on a light coloured jacket. The leaves of infested plants will be shot-holed. Pheromone traps can be used to monitor moth activity. Although these traps cannot predict the size of an outbreak, the trap counts can provide an early warning of an infestation. It takes a severe infestation of small larvae to cause appreciable damage.
Damage is most noticeable during dry summers.
There have been reports of up to 415 larvae per plant during severe infestations. If pod damage begins to show when the larvae are still small and numerous, control measures are definitely warranted. Note that, if the moths are blown in from the south early or if the canola is sown late, the larvae may feed on the developing buds of canola. If this happens, the economic thresholds would be much lower than when larvae feed on the pods. Control Tips Check with provincial agricultural representative for timing of applications.