Armyworms

Beet armyworm (Spodoptera exigua)
Bertha armyworm (Mamestra configurata)
Yellowstriped armyworm (Spodoptera ornithigalli)

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Beet armyworm larvae
Bee armyworm larva.

five Bertha army worm larvae
Bertha armyworm larvae collected from canola.

yellowstriped armyworm feeding on hemp leaf
Yellowstriped armyworm larva found on hemp.

beet armyworm eggs on leaf
Beet armyworm eggs.

Hosts

  • Field-grown hemp
  • Legumes
  • Brassicas
  • Leafy Greens
  • Cucurbits
  • Solanaceae Crops
  • Root Crops
  • Many herbaceous ornamentals

Appearance

Larvae are generally light green and marked with thin green-yellow stripes running the length of the body. Beet armyworms have a small black spot on each side of the second body segment behind the head. Yellowstriped armyworms vary in color from green to black. They have two yellow to orange stripes along the back, a dark spot on the sides of the fourth body segment behind the head, and black triangles along either side of the back. Bertha armyworms are green to black with a pale stripe on each side of the body. When disturbed, larvae of all species will curl into a c-shape. Adult moths are mottled gray and brown with light-colored markings on the wings and a wingspan of 25 to 45 mm. Eggs are small, pale white to yellow, ribbed, and usually found on the undersides of leaves in masses of 50 or more; eggs may be partially covered by hairs from the moth.

Damage Symptoms

Larvae feed on leaves with chewing mouthparts, causing skeletonized foliage (young larvae), irregular holes, shredded leaves, or defoliation (older larvae). Young larvae feed in groups while older larvae feed alone. Webbing (silk) may be associated with the damage. In hemp, larvae may move into maturing buds at high populations. 

Life Cycle

Egg | Larva | Pupa | Adult 

  • 2-3 generations per growing season.
  • Overwinter as pupae in the soil.
  • Moths emerge from March to July, mate, and females lay eggs in clusters on host plants.
  • Larvae feed for 5-8 weeks before pupating in the soil.
  • Larvae of 2nd generation may be seen until early October before pupating in the soil to overwinter.
Damaging Lifestage(s): Larva

Time for Concern

Primarily July through September.

When and Where to Scout

  • Scout plants biweekly from field planting to harvest for the presence of egg masses and/or larvae.
  • Egg masses and groups of larvae are found on the undersides of leaves.
  • Maturing larvae may be found singly towards the center of the plant or may be seen in the soil.

Threat Level

Low to medium. 

Occurrence in Utah

Very few caterpillars have been found on field-grown hemp with little foliar damage. 

Management

  • Keep crop area weed-free.
  • Till the field in after harvest to expose overwintering pupae.
  • Scout plants biweekly throughout the growing season for egg masses and larvae.
  • First (spring/early summer) generation larvae are likely to cause little damage; second generation larvae may damage leaves and spread to flower buds.
  • Approved insecticides are available. One option is Bacillus thuringiensis (Bt), which must be consumed, so it should only be used when caterpillars are less than one-half inch in size.

When to Consider Treatment

Larvae of second generation have a greater capacity to cause significant damage to leaves and buds.

Look-alikes

Other larvae in the Noctuidae family.

Caterpillar Insecticides

Utah-Registered Product Active Ingredient(s) Notes
Agree WG Bacillus thuringiensis ssp. aizawa  
Aza-Direct Biological Insecticide azadirachtin  
AzaGuard  azadirachtin  
AzaSol azadirachtin  
Azatin O Biological Insecticide azadirachtin  
Azatrol EC Insecticide azadirachtin  
Azera Insecticide azadirachtin  
BT Now Bacillus thuringiensis ssp. kurstaki Greenhouse use only.
Bug Buster-O Extinguish Ant Bait pyrethrins Greenhouse use only.
Deadzone diatomaceous earth  
Deliver Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
DiPel DF Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
DiPel DF Biological Insecticide Dry
Flowable		 Bacillus thuringiensis ssp. kurstaki  
DiPel PRO DF Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
Evergreen Crop Protection EC 60-6 pyrethrins  
Ferti-Lome Dipel Dust Biological Insecticide (RTU) Bacillus thuringiensis ssp. kurstaki  
Ferti-lome Fruit Tree Spray pyrethrins  
Grandevo CG;WDG Chromobacterium sub strain PRAA4-1 cells  
Javelin WG Biological Insecticide Bacillus thuringiensis ssp. kurstaki  
Leprotec Bacillus thuringiensis ssp. kurstaki  
Molt-X azadirachtin  
Neemix 4.5 Insect Growth Regulator azadirachtin  
Prizefighter ammonium nonanoate  
Pycana  pyrethrins Greenhouse use only.
Pyganic Crop Protection EC 1.4 II; 5.0 II pyrethrins  
SPEAR-LEP gs-omega/kappahxtx-hv1a Supression only; combine with a Bt product for greater efficacy.
Tersus Insecticide pyrethrins  
Thuricide N/G Bacillus thuringiensis ssp. kurstaki  
Valent Professional Products DiPel Pro DF Biological Insecticide Dry
Flowable		 Bacillus thuringiensis ssp. kurstaki  
Venerate CG Burkholderia sp. strain A396  
XenTari Biological Insecticide Dry Flowable Bacillus thuringiensis ssp. aizawai  

Photo Credits

  • Beet armyworm - John Capinera, University of Florida, Bugwood.org
  • Bertha armyworm - Canola Council of Canada
  • Yellowstriped armyworm - USU Extension IPM Program
  • Eggs - Ronald Smith, Auburn University, Bugwood.org
Precautionary Statement: Utah State University and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document. All pesticides are labeled with ingredients, instructions, and risks, and not all are registered for edible crops. “Restricted use” pesticides may only be applied by a licensed applicator. The pesticide applicator is legally responsible for proper use. USU makes no endorsement for any specific brand-name products listed on this page.