Agriculture: Strawberry Pest Management Guidelines

Cutworms

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

    The black cutworm, also called the greasy cutworm, is the primary cutworm pest of strawberries in most growing areas, but other species occur in damaging numbers on occasion. Cutworm adults are large moths, usually brown or gray, about 1.5 inches long. Mature larvae are robust, nearly 1.5 inches long, and their smooth skin is either mottled brown or gray. Larvae tend to fall to the ground and curl up into a C-shape when they are disturbed.

    Cutworms are active night feeders and can be found hidden in the soil at the base of the plant during the day. Most cutworms overwinter in strawberries as young larvae, maturing and pupating in spring. Since there are only a limited number of hosts in fall for adult moths to lay eggs on, they tend to move into newly planted strawberry fields. Migration of adult moths can also occur following harvest of other hosts, such as lettuce, in nearby fields.

    Damage

    Early season damage by newly hatched cutworms generally appears as small, webless perforations in the newly expanding crown leaves. As larvae grow, they begin their characteristic stem cutting along with chewing larger, irregular holes in the foliage. At times, serious damage can occur to the plant crown when the central growing point of young plants is eaten.

    Damage often occurs along the edges of fields adjacent to residential areas or to more favored crops such as lettuce or beans. Most damage occurs in fall and spring, with the fall attack being more destructive. During harvest, cutworms can cause rather pronounced holes in the fruit. Damaged berries tend to be concentrated in localized areas of one to several plants around each active cutworm.

    Management

    Watch edges of fields to detect cutworm invasions. Controlling weeds in and around the field is important to manage this pest. If damage is occurring, use insecticidal baits or make spot treatments.

    Biological Control

    Other than birds, there isn't much significant biological control known. The most important control is cultural.

    Cultural Control

    Weed control is paramount to preventing a serious cutworm problem. Weedy fields tend to attract more moths to lay their eggs. Annual planting and thorough pruning of second-year plantings reduce survival of overwintering larvae.

    Organically Acceptable Methods

    Use cultural controls and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad on organically certified strawberries.

    Monitoring and Treatment Decisions

    There is no specific threshold for treating cutworms. Damage tends to be localized, so spot treating is recommended if using foliar sprays. For best results when applying foliar sprays, spray late in the day or evening. When using insecticidal baits, make applications immediately after weeding when evidence of substantial leaf or stem cutting is noted in order to prevent migration to the crop plants.

    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.
     
    Baits
     
    A. SPINOSAD
      (Seduce) Label rates 4 1
      MODE-OF-ACTION GROUP NUMBER1: 5
     
    Foliar sprays
     
    A. MALATHION
      (Malathion 8E) Label rates 12 3
      MODE-OF-ACTION GROUP NUMBER1: 1B
      COMMENTS: Some formulations can be applied through the drip lines, which allows application under the plastic where cutworms can hide. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
     
    B. DIAZINON*
      (Diazinon AG600 WBC) 12.75 fl oz/100 gal water 72 (3 days) 5
      MODE-OF-ACTION GROUP NUMBER1: 1B
      COMMENTS: Do not allow this insecticide to run off into surface waters. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
     
    C. SPINOSAD
      (Entrust)# 1.25–2 oz 4 1
      (Success) 4–6 fl oz 4 1
      MODE-OF-ACTION GROUP NUMBER1: 5
      COMMENTS: Apply against younger larvae or when fruit feeding is observed. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
     
    D. BACILLUS THURINGIENSIS ssp. KURSTAKI#
      (various products) Label rates 4 0
      MODE-OF-ACTION GROUP NUMBER1: 11A
      COMMENTS: Spray when young larvae present. Good coverage at relatively low dilution is essential.
     
    E. BACILLUS THURINGIENSIS ssp. AIZAWAI#
      (Agree WG) Label rates 4 0
      MODE-OF-ACTION GROUP NUMBER1: 11A
      COMMENTS: Spray when young larvae present. Good coverage at relatively low dilution is essential.
    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.
    # Acceptable for use on organically grown produce.
    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).
    Text Updated: 07/18
    Treatment Table Updated: 07/18