| ||Insect life cycle | Damage assessment | Management strategy
Insect Life Cycle
Although considered general feeders, alfalfa loopers prefer alfalfa, clover and lettuce. Other hosts include canola, peas, spinach and various garden crops, ornamental trees and tree fruits. Damage to canola occurs sporadically in northern and southern Alberta.
Found throughout Alberta, alfalfa loopers may overwinter in the pupal stage. However, most of the Alberta population is blown in from the United States each year.
Early summer moths are likely to be migrants from the United States. The moths appear all summer long because generations overlap. Moths feed on flower nectar at dusk and fly during daylight hours.
Number of generations
There are two or three generations per year.
Pathogens - A virus disease will usually control late-season infestations.
Alfalfa loopers are an occasional pest in Alberta. Larvae are present from mid June through September. Small larvae feed on leaf surfaces and medium-sized larvae eat ragged holes through leaves. Older larvae feed along leaf margins and may defoliate a large portion of the plant as well as clip flowers and seed pods. The actual decrease in yield that results from this feeding damage is not known. Compensation by plants for such injuries may include continued or additional stooling. The plants may also have more flowers and set more and larger seed. Flower clipping is the most significant problem in canola, but the plant can normally compensate unless severe damage occurs.
Beat plants in an area 50 cm x 50 cm and record the number of larvae on the ground. Repeat this procedure several times in different locations to obtain an average number of larvae per square metre for the field.
Damage occurs through defoliation and clipping of flowers and immature seed pods. No economic threshold has been established. However, more than 15 larvae per square metre, combined with heavy defoliation or flower and pod clipping, may warrant control.
Avoid growing canola near alfalfa.
If an infestation occurs, assess the damage to plants and sample the field to determine the numbers of larvae. Delay an insecticide application as long as possible to allow diseases to control the pest. Historically, the pest has been adequately controlled by viral diseases.