How to Manage Pests

UC Pest Management Guidelines

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.

PUBLICATION

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 Co.
P. A. Phillips, UC IPM Program/UC Cooperative Extension Ventura Co.
Acknowledgment for contributions to the Insects and Mites:
N. C. Toscano, Entomology, UC Riverside

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