Bean: Cutworms and armyworms

Biology

Cutworms and armyworms are the larvae of noctuid moths. These common moths are medium-sized with fairly dull coloration. The greenish, grayish, or tan caterpillars are hairless, nocturnal, and generally spotted, striped, or otherwise marked. They may be 1⁄4″ to 1″ in length and tend to curl up when disturbed. Cutworms may feed by cutting through stems of young plants an inch or less above ground level. Several plants may be damaged in one night. They may also climb into the plant and feed on foliage and chew holes in developing pods and seeds. While armyworms typically feed during the day, cutworms spend the day just beneath the soil surface or under debris near the host. They usually feed at night, so it is advisable to search for them with a flashlight in the dark. Weeds are their primary food source.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Control weeds and grasses in and near the garden.
• Remove debris around plants that provides shelter for cutworms.
• Hand-pick night-feeding larvae, when practical. Scratch soil at the base of damaged plants to find larvae in the daytime.
• Encourage natural enemies of cutworms including birds and spiders.
• Plastic or cardboard collars extending 2″ into the soil and 2″ above the soil can be placed around individual plants or groups of plants. The barrier may help prevent cutworm attack.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• Apply when damage first appears.
• Cutworms are difficult to control.
• Bacillus thuringiensis will provide some control if caterpillars eat enough of it.
• Use a spreader-sticker with liquid Bt formulations.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Bonide Captain Jack's Deadbug Brew R-T-U [Organic]
  Active ingredient: spinosad (spinosyn A+D) [EPA registration number: 4-472]
• Bonide Pyrethrin Garden Insect Spray Concentrate
  Active ingredient: pyrethrins [EPA registration number: 4-371]
• Bonide Thuricide BT Concentrate
  Active ingredient: Bacillus thuringiensis subsp. kurstaki [EPA registration number: 4-226]
• Bug Buster-O [Organic]
  Active ingredient: pyrethrins [EPA registration number: 1021-1771-54705]
• Safer Brand BioNEEM Multi-Purpose Insecticide and Repellent Concentrate [Organic]
  Active ingredient: azadirachtin [EPA registration number: 70051-6-42697]
• This list may not include all products registered for this use.

Additional Images