Bertha armyworm – caterpillar

Mike Dolinski, [email protected]

Hosts

Feeding Damage

Identification

MATURE LARVAE: In canola, larvae move from leaves to pods where they either “debark” the pods, chew into them to eat the seeds, or totally consume pods. Severely stripped pods may prematurely shatter. Crops can take on a frosted appearance. In flax, they cut flowers and developing bolls.

Canola, mustard, alfalfa, lamb’s-quarters and related plants; occasionally attack peas, flax, potato, and other plants. ADULTS: 20 mm long, greyish body with 40 mm wing span; characteristic wing markings on the forewing include a prominent, white, kidneyshaped marking near the midpoint, and a conspicuous white and olive-colored, irregular transverse marking near the tip.

Armyworm, Bertha

Mamestra configurata (Walker)

Lepidoptera

MATURE LARVAE: 40 mm long, velvety black (occasionally light green or light brown) caterpillars with a light brown head and a broad, yellowishorange stripe along each side and three narrow, broken white lines down their backs. Jan

Feb

Overwintering

Mar

Apr Eggs

May

June

Larvae

July Pupae

Aug

Sept Adults

Oct

Nov

Dec

ADULTS: Feed on nectar from flowers.

Similar Species

Clover cutworm larvae (p. 86) look similar but the lateral band is yellowish-pink, and there are more greenish or brown along with black larvae than among bertha armyworm infestations.

Life Cycle

Overwinter as pupae 5–16 cm below soil surface; round ridged eggs are laid in clusters on underside of leaves; females are attracted to blooming host crops.

Bertha armyworm – caterpillar (green form) Alberta Agriculture and Rural Development

Bertha armyworm – eggs AAFC

Bertha armyworm – caterpillar (green form) Alberta Agriculture and Rural Development

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Field Crop and Forage Pests and their Natural Enemies in Western Canada: Identification and Management Field Guide

PESTS Monitoring/Scouting

Management Options

Economic Threshold

CULTURAL: Recommended practices include crop rotation with non-crops, effective control of weed hosts, early swathing (minimize larval feeding) and fall cultivation (expose pupae). Do not kill nearby infested weed hosts while the crop is susceptible to feeding damage.

Bertha armyworm – damage

Mike Dolinski, [email protected]

Tables are available on provincial government web sites that show the economic thresholds for canola at different crop values and costs of chemical control.

Bertha armyworm – damage AAFC

BIOLOGICAL: Several diseases and natural enemies attack eggs and larvae, including a nuclear polyhedrosis virus, an ichneumonid wasp (Banchus flavescens Cresson (p. 131)), a tachinid fly (Athrycia cinerea (Coquillett) (p. 119)), and an egg parasitoid (Trichogramma inyoense Riley (p. 134)).

CHEMICAL: Several products are available for application as dictated by scouting. Apply in mid-morning or early evening when more larvae are feeding at the top of the crop canopy.

Lepidoptera

Provincial forecast maps (based on male moths caught in pheromone-baited traps), are posted on-line indicating the annual risk of an infestation. When canola crop is in the early pod stage (stages 5.1–5.2), count the number of larvae in a 0.25 m2 area in 10–15 different locations spaced at least 50 m apart following a zigzag pattern. Shake the plants to dislodge the larvae and then remove leaf debris and soil clumps to expose the larvae for counting. Calculate the number of larvae/m2.

Bertha armyworm – adult

Alberta Agriculture and Rural Development

Bertha armyworm – damage

Alberta Agriculture and Rural Development

Descriptions of Field Crop Pests

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