The diamondback moth, known formally as Plutella xylostella, was introduced into North America in the mid-1800s.
It’s now present across the continent, wherever its host plants are grown. Diamondback moth larvae feed on all plants in the mustard family. In Western Canada, canola and mustard are its primary targets.
Although present every year on the Prairies and Plains, the severity of the infestation is variable; 1995 was the last widespread infestation.
Damage is done by the larvae, which usually devour only a small portion of leaf. Larvae work on the underside and eat many small “shot holes.”
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They also feed on buds, flowers, seed pods, the green outer layer of the stems and occasionally the developing seeds within older seed pods. The amount of damage varies, depending on plant growth stage, larval densities and size.
When plants begin to flower, larger larvae often feed on flower buds, flowers and young seed pods. Damage can be extensive during the early flowering stage. Heavy flower feeding will delay plant maturity, cause the crop to develop unevenly and significantly reduce seed yields.
When canola or mustard are fully podded and leaves begin to wilt or die in late July or early August, larvae will remove the surface tissue from the stems and seed pods. The seeds within a damaged pod will not fill completely and pods may shatter. Larvae may also chew into seed pods and eat the developing seeds.
Crop damage is usually first evident on plants growing on ridges and knolls. It can be prevented only by early field monitoring and insecticide application.
Economic thresholds are two to three larvae per plant or 10 to 15 per sq. foot during early flowering and 20 to 30 per sq. foot during early pod ripening.
