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How to Manage Pests

UC Pest Management Guidelines

Variegated cutworm, Peridroma saucia, larva.



Scientific names:
Black cutworm: Agrotis ipsilon
Variegated cutworm: Peridroma saucia

(Reviewed 8/07, updated 5/08)

In this Guideline:


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.


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.


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 (108 KB, 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 form108 KB, PDF). Treatment is necessary where worms are abundant and before the tubers are damaged.

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

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees and environmental impact Not all registered pesticides are listed. Always read label of product being used.
  (Sevin) 5% Bait 20–40 lb 12 7
  (Lannate LV) 1.5 pt 46 6
  COMMENTS: Not recommended in fields where potato psyllids are present because it promotes their population development.
** See label for dilution rates.
+ 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.
* Permit required from county agricultural commissioner for purchase or use.
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/.




[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Potato
UC ANR Publication 3463
L. D. Godfrey, Entomology, UC Davis
D. R. Haviland, UC Cooperative Extension, Kern Co.

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