Armyworms and Cutworms

(Several species)

Insects and Invertebrates

 

Symptoms
Armyworm caterpillars and climbing cutworms feed on young leaves and primary buds which can reduce crop yield. Armyworm caterpillars feed in colonies shortly after hatching; feeding on and skeletonizing leaves. Cutworms are an early season pest and feed on primary buds which can reduce production by up to 50% in infested areas. These pests can be serious harvest contaminants in machine harvested fields.

Although damage is similar, armyworms are distinct from cutworms in their behavior. While cutworms are usually solitary feeders, armyworm eggs are laid in masses and larvae will feed as a group. When populations are high and food is scarce, armyworms will move as a group, feeding indiscriminately on plants in their path.

 

 

Identification
Several species of armyworms and cutworms attack caneberries. Cutworms are plump, smooth and often greasy-looking. Typically, cutworms curl up tightly when disturbed. They have greenish, brownish, grayish, or striped bodies, up to 1 ¾ inches long. Although about the same size, armyworms differ in appearance. True armyworms are plump, sparsely-haired, generally green to brown larvae, with dark longitudinal stripes running down the sides and back. White or greenish eggs are laid in masses and darken as they approach hatching.

 

 

Life History
Adult cutworm and true armyworm moths first appear between April and July. Moths generally fly at night and rest during the day under shelter. Females lay single eggs or egg masses on the lower leaves of host plants over a 2 to 3 week period. The caterpillars usually remain hidden during the day and feed at night. A second or third generation of cutworms may emerge in the summer and early fall. Some species overwinter as a naked pupa in the soil, while some larvae continue to develop through the winter. Armyworm larvae have six growth stages, or instars. The armyworms final instar lasts about 10 days and they consume large amounts of plant material during that time.

 

 

Monitoring
Cutworms are usually not evenly distributed across a field and are rather found in “hot spots”. Scout 3-5 sites per field, (depending on field size) and evaluate 10-20 hills, spaced 3-5 hills apart on both sides of the aisle way.

In early spring, begin examining buds and new growth for signs of feeding damage and record the percentage of infested hills. Where damage is found, scratch the soil around the base of the plant during the day to identify the pest. If not found, check at night with a flashlight when worms are active.

In late spring/ early summer, begin monitoring the plant canopy using a beating tray. Take 10 beating tray samples and record the total number of armyworm/ cutworm dislodged from the foliage. Hold tray about one foot below the trellis wire within canopy and shake foliage by grasping wire with hand and shaking, or striking top wire three times with rubber sprayer hose to dislodge insects.

During harvest, ride harvester to see what insect contaminants are coming across the belt. This is one of the best methods to evaluate the effectiveness of your pre-harvest spray. Train workers on harvesting machines to communicate presence of armyworms, cutworms or other contaminants. Keep a container for the workers to deposit insect contaminates, which can be used to evaluate their numbers.

 

Thresholds and Management
No threshold or tolerance level available.

If larvae are found at significant levels, a chemical spray treatment is recommended. Proper timing of application is extremely important because once larvae become active in spring they can cause serious bud damage in a short time.

Many of these caterpillars have strong preferences for certain species of weeds. Fields surrounded by, or overgrown with weeds tend to have more serious cutworm and armyworm problems. Control weeds, grasses and other debris in the field that may provide cover.

 

Resources
Washington State University, Small Fruit Pests: Biology, Diagnosis and Management
Small Fruit Pests EB1388

Pacific Northwest Insect Management Handbook
https://pnwhandbooks.org/insect

Cornell University, New York State Integrated Pest Management Program: Climbing Cutworms.
https://ecommons.cornell.edu/items/c8b71f6d-a65b-49f4-a363-92c136090bf5

Washington State University, Tree Fruit Research and Extension Center: Noctuid Pests in Washington Orchards
https://treefruit.wsu.edu/crop-protection/opm/lacanobia/

Washington State University, Tree Fruit Research and Extension Center: Fruitworms, armyworms and climbing cutworms
https://treefruit.wsu.edu/crop-protection/opm/fruitworms/