How to Manage Pests

UC Pest Management Guidelines

Alfalfa

Variegated and Other Cutworms

Scientific Names:
Granulate cutworm: Agrotis subterranea
Variegated cutworm: Peridroma saucia

(Reviewed 11/06, updated 11/06, corrected 9/10)

In this Guideline:


DESCRIPTION OF THE PESTS

Cutworms are only occasional pests of high desert and Central Valley alfalfa but are frequent pests in the low desert where alfalfa is planted on beds. The granulate and the variegated cutworms are the two species that most commonly attack low desert alfalfa.

Female moths lay white or greenish eggs in irregular masses on leaves or stems of plants, often near the base of the plant. Eggs darken as they approach hatching. Full grown caterpillars are about 1.5 to 2 inches long and appear as smooth-skinned caterpillars of various colors and patterns. Larvae frequently roll into a C-shape when disturbed. Cutworms feed at night and hide during the day in soil cracks and under debris and loose soil.

DAMAGE

In the Central Valley, variegated cutworm populations may develop in weedy areas and migrate into seedling stands or occasionally mature stands. Injurious populations usually occur from April to late June. Seedling alfalfa stands can be severely damaged by cutworms cutting the seedlings off at or just below the soil surface. Established fields are damaged when cutworms cut off new growth or feed on the alfalfa foliage.

Granulate cutworm is a devastating pest of bed-planted alfalfa and can also be a pest of alfalfa planted between borders. Low desert alfalfa fields are attacked from May through October, but the pest occurs year round in fields. Established alfalfa fields can be severely injured when cutworms cut off new shoots at or below ground level following harvest. The pest often goes undetected after cutting and hay removal but the problem becomes apparent when the field is irrigated and there is little or no regrowth.

MANAGEMENT

Tillage, flood irrigation, and weed control are important in cutworm management. When damage is severe in seedling fields, apply an insecticide bait.

Cultural Control

Tillage helps to limit cutworm populations; seedlings in well-tilled fields—especially when there is an interval between crops—are less likely to have cutworm problems. Keep the field and field edges weed-free. Flood irrigation can drown many cutworm larvae. Flood irrigation during the day will attract many birds that prey on the cutworms as the advancing water forces larvae from hiding.

Organically Acceptable Methods

Cultural controls are acceptable for use on an organically certified crop.

Monitoring and Treatment Decisions

Cutworm infestations are sporadic, and treatment guidelines have not been established in California. Check for cutworms by looking under duff and carefully digging to a depth of 1 inch in loose soil near alfalfa crowns. When cutworm numbers exceed one or two per foot of row or severe damage is apparent, it may be necessary to treat. If treating with baits, apply baits in late evening or at night when cutworms are on 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, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. PERMETHRIN*
  (Pounce) 25WP, 3.2EC, WSB Label rates 12 14
  (Ambush) 25WP 8.2–12.8 oz 12 14
  MODE OF ACTION: A pyrethroid (Group 3)1 insecticide.
 
B. CYFLUTHRIN*
  (Baythroid) 2E 0.8–1.6 fl oz 12 7
  (Renounce) 20WP 1–2 oz 12 7
  MODE OF ACTION: A pyrethroid (Group 3)1 insecticide.
 
C. LAMBDA-CYHALOTHRIN*
  (Warrior) 1.92–3.2 fl oz 24 7 – hay; 1 – forage
  MODE OF ACTION: A pyrethroid (Group 3)1 insecticide.
  COMMENTS: Do not apply when bees are actively foraging. Do not apply more than 0.24 pt/acre/cutting or 0.96 pt/acre/season.
 
D. INDOXACARB
  (Steward) 1.25 SC 6.7–11.3 fl oz 12 7
  MODE OF ACTION GROUP NUMBER1: 22A
  COMMENTS: Make no more than one application per cutting. Not for use in alfalfa grown for seed or for sprouts for human consumption. Do not apply more than 45 fl oz/acre/crop season.
 
**   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 until the field can be grazed or cut. In some cases the R.E.I. exceeds the P.H.I.; the longer of these two intervals is the minimum time that must elapse before harvest may take place.
* Permit required from county agricultural commissioner for purchase or use.
1 Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is 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: Alfalfa
UC ANR Publication 3430

Insects and Mites

  • C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
  • L. D. Godfrey, Entomology, UC Davis
  • M. Rethwisch, UC Cooperative Extension, Riverside County (Blythe)
  • D. R. Haviland, UC Cooperative Extension, Kern County
  • P. B. Goodell, Entomology, Kearney Agricultural Center, Parlier
  • R. F. Long, UC Cooperative Extension, Yolo County

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