Agriculture: Potato Pest Management Guidelines

Cutworms

  • Black cutworm: Agrotis ipsilon
  • Variegated cutworm: Peridroma saucia
  • Description of the Pest

    The most common species encountered are the black cutworm and the variegated cutworm. The adults are dull-colored brown to grayish moths. The larvae are usually earthen-colored with various stripes or spotted color patterns. They are smooth-bodied worms that may be 2 inches in length when mature. Many species curl into a C-shape when disturbed.

    Damage

    Cutworms may cut off the stems of young plants during stand establishment. Later in the season they feed on foliage. Tubers that are exposed on the soil, or by cracks, or are set very shallow may be damaged. Cutworm damage to tubers appears as a gouged out cavity.

    Management

    Cutworms are not an annual problem, nor are they a problem in every field. Weed control in and around the field before planting will reduce cutworm problems through reduction of early season host plants. Treatment thresholds have not been established. Monitor the field (PDF) to detect cut plants and foliar feeding early in the season. Later in the season, inspect plants for foliage damage. Also, shake the plants over a beating cloth placed in the row and inspect the beds and furrows for larvae, and inspect shallow set and exposed tubers for damage. Keep records of your monitoring results (example formPDF). Treatment is necessary where worms are abundant and before the tubers are damaged.

    Common name Amount per acre** REI‡ PHI‡
    (Example trade name) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
     
    A. CARBARYL
      (Sevin 5% Bait) 20–40 lb 12 7
      MODE OF ACTION GROUP NUMBER1: 1A
     
    B. METHOMYL*
      (Lannate LV) 1.5 pt 48 6
      MODE OF ACTION GROUP NUMBER1: 1A
      COMMENTS: Not recommended in fields where potato psyllids are present because it promotes increases in their numbers.
    C. LAMBDA-CYHALOTHRIN
      (Warrior II with Zeon) 0.96–1.60 fl oz 24 7
      MODE OF ACTION GROUP NUMBER1: 3A
      COMMENTS: Not recommended in fields where potato psyllids are present because it promotes increases in their numbers.
    ** See label for dilution rates.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
    * Permit required from county agricultural commissioner for purchase or use.
    1 Rotate insecticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers for insecticides and miticides (un=unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).

    Important Links

    Text Updated: 04/19
    Treatment Table Updated: 04/19