WSU Extension


Common and yellow mosaics 
Curly top (Beet curly top virus) 
Fusarium root rot 
Gray mold 
White mold (Sclerotinia rot) 
Bean aphids 
Brown marmorated stink bug 
Cutworms and armyworms 
Spider mites 

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Caption: Spotted cutworm
Photo by: K. Grey
Bean : Cutworms and armyworms
(revision date: 3/10/2017)

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

Non-Chemical Management
  • 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.
Select non-chemical management options as your first choice!

Chemical Management

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.

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 reg no: 4-472
  • Bonide Pyrethrin Garden Insect Spray Conc.
    Active ingredient: pyrethrins  |  EPA reg no: 4-371
  • Bonide Thuricide BT Conc
    Active ingredient: Bacillus thuringiensis subsp. kurstaki  |  EPA reg no: 4-226
  • Bug Buster-O [Organic]
    Active ingredient: pyrethrins  |  EPA reg no: 1021-1771-54705
  • Safer Brand BioNEEM Multi-Purpose Insecticide & Repellent Conc [Organic]
    Active ingredient: azadirachtin  |  EPA reg no: 70051-6-42697
  • Safer Brand Garden Dust RTU [Organic]
    Active ingredient: Bacillus thuringiensis subsp. kurstaki  |  EPA reg no: 36488-25-42697
  • This list may not include all products registered for this use.

+ Show larger images

Caption: Spotted cutworm
Photo by: K. Grey
Caption: Bertha armyworm
Photo by: K. Grey
Caption: Cutworm eggs
Photo by: A.L. Antonelli
Caption: Western yellow stripe armyworm adult
Photo by: A.L. Antonelli