How to Manage Pests

UC Pest Management Guidelines

Sugarbeet

Cutworms

Scientific names:
Pale western cutworm: Agrotis orthogonia
Black cutworm: Agrotis ipsilon
Granulate cutworm: Feltia (=Agrotis) subterranea
Variegated cutworm: Peridroma saucia
Army cutworm: Euxoa auxiliaris

(Reviewed 11/05, updated 1/10)

In this Guideline:


DESCRIPTION OF THE PESTS

The pale western cutworm is a large (1.5 to 2 inches when fully grown) grayish caterpillar with no conspicuous markings except for a dark inverted V on the head. They live in the soil at the base of plants and are thus not seen until damage is apparent.

The black cutworm larva is gray to dark brown above and has a greasy appearance. Faint light stripes run lengthwise down the body. It also lives in soil, and like the pale western cutworm is usually not seen until damage is found.

The granulate cutworm is about an inch long when mature, dark gray in color, and the surface of its body is covered with black granules. It lives in the soil and cuts plants off below ground.

The variegated cutworm is a dark gray caterpillar with a light stripe on the side and small yellow to orange spots on top of the abdominal segments. Fully-grown larvae may be 1.5 to 2 inches long. Variegated cutworm is a climbing species, and while mostly nocturnal, may frequently be found feeding during the day.

The army cutworm is pale greenish gray to brown with the back pale-striped and finely splotched with white and brown.

Several other species of cutworms may be found in sugarbeets and their habits and control are similar to the species listed above.

DAMAGE

The subterranean species (pale western, black, and granulate cutworms), feed largely underground, cutting plants off below the soil line. Frequently, many plants in a row will be cut off during the night; often this is the first indication of a problem. The black cutworm is especially active and has the habit of cutting off many plants while feeding. The granulate cutworm is primarily a pest of sugarbeet grown near alfalfa in the Imperial Valley. On occasion it migrates out of the alfalfa fields into sugarbeet, where it can consume young plants or clip them off below the ground as they feed. Granulate cutworm moths have been found to lay eggs on sugarbeet, and hatching larvae kill plants by eating them to the ground or by clipping them off at ground level, thus reducing plant stands.

The variegated and army cutworms are aboveground feeders and cut the plants off at or above the soil line. They also climb onto older plants and feed mostly on young foliage in the center of the crown. They generally cause only minor damage at this point.

MANAGEMENT

Biological Control

Cutworms are attacked by a number of predators, parasites, and diseases. Many of these natural control agents are not effective on pale western and black cutworms because of their subterranean nature. It is not known if any of these natural enemies can control cutworm populations, but their presence should be noted.

Cultural Control

Cutworms often build up in rotation crops preceding sugarbeet, such as alfalfa and cereals. If surveys indicate the presence of substantial numbers of cutworms in these crops, sugarbeet should not be planted. Spring plowing and discing are also useful in reducing cutworm numbers. Keep fields weed-free, especially eliminating grassy weeds that serve as alternate hosts for cutworms. Cutworms may also build up in high numbers if grassy weeds are prevalent in the crop preceding sugarbeets.

Monitoring and Treatment Decisions

Monitor for cutworms during stand establishment by looking for plants lying on their sides that have been chewed at the soil surface or that are completely missing. If plants are missing completely, gently dig in the area where a seedling would be expected to try to find the intact root system as evidence of cutworm damage.

No economic thresholds have been established for cutworms, and the decision to treat depends on the severity of injury. Organophosphate (chlorpyrifos) and carbamate (methomyl, carbaryl) insecticides do not control the granulate cutworm; check with your farm advisor concerning the availability of materials to control this pest.

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 the order of usefulness in an IPM program, taking into account efficacy and impact on natural enemies and honey bees as well as the environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. METHOXYFENOZIDE
  (Intrepid) 2F 4–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: Provides suppression of cutworms.
 
B. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11
 
C. CHLORPYRIFOS*
  (Lorsban Advanced) 2 pt 24 30–tops and roots
  (Lorsban 15G) 8 oz/1000 row ft 24 30
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Do not make more than 1 application of 15G per year. Avoid drift and tailwater runoff into surface waters or choose alternative materials.
 
D. METHOMYL*
  (Lannate) LV 1.5 pt 48 21–roots
  MODE OF ACTION GROUP NUMBER1: 1A 30–tops
 
E. CARBARYL*
  (Sevin) 80S 1.87 lb 12 28–roots and forage
  MODE OF ACTION GROUP NUMBER1: 1A
 
+ 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 more information, see www.irac-online.org.
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Sugarbeet
UC ANR Publication 3469

Insects and Mites

E.T. Natwick, UC Cooperative Extension Imperial County
Acknowledgement for contributions to Insects and Mites:
C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
D. R. Haviland, UC IPM Program, Kern County
L. D. Godfrey, Entomology, UC Davis

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