How to Manage Pests

UC Pest Management Guidelines

Strawberry

Cutworms

Scientific Names:
Black cutworm: Agrotis ipsilon
Roughskinned cutworm: Athetis mindara
Variegated cutworm: Peridroma saucia

(Reviewed 6/08, updated 5/10)

In this Guideline:


DESCRIPTION OF THE PESTS

The black cutworm, also called the greasy cutworm, is the primary cutworm pest of strawberries in most growing areas but other species are found 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 backyards 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 an important aspect of managing this pest. If damage is occurring, use 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
Cultural controls and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are acceptable for use 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, treat late in the day. When using baits, make applications immediately after weeding when evidence of substantial leaf and/or stem cutting is noted in order to prevent migration to the crop plants.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. MALATHION Label rates 12 3
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Some formulations can be applied through the drip lines, which allows treating under the plastic where cutworms can hide.
 
B. DIAZINON* 12.75 fl oz/100 gal water 3 days 5
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Do not allow this material to run off into surface waters.
 
C. SPINOSAD
  (Entrust)# 1.25–1.5 oz 4 1
  (Success) 6 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Apply against younger larvae or when fruit feeding is observed.
 
D. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11
  COMMENTS: Treat when young larvae present. Good coverage at relatively low dilution is essential.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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.
# Acceptable for use on organically grown produce.
1 Rotate chemicals 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; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468

Insects and Mites

  • F. G. Zalom, Entomology, UC Davis
  • M. P. Bolda, UC Cooperative Extension, Santa Cruz County
  • S. K. Dara, UC Cooperative Extension, Santa Barbara County
  • S. Joseph, UC Cooperative Extension, Monterey County
Acknowledgment for contributions to the Insects and Mites:
  • P. A. Phillips, UC IPM Program and UC Cooperative Extension, Ventura County
  • N. C. Toscano, Entomology, UC Riverside

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