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How to Manage Pests

UC Pest Management Guidelines


Color variations of tomato fruitworm (also called corn earworm and cotton bollworm).

Spinach

Caterpillars (Lepidopterous Pests)

Scientific Names:
Beet armyworm: Spodoptera exigua
Cabbage looper: Trichoplusia ni
Corn earworm: Helicoverpa zea
Black cutworm: Agrotis ipsilon
Variegated cutworm: Peridroma saucia
Granulate cutworm: Agrotis subterranean
Western yellowstriped armyworm: Spodoptera praefica

(Reviewed 12/09, updated 12/09)

In this Guideline:


DESCRIPTION OF THE PESTS

Beet armyworms lay their eggs in distinctive cottony masses on leaf surfaces. Newly hatched beet armyworms are small, green worms that often feed in groups. Older beet armyworms vary in color, but usually have many fine, wavy, light-colored stripes down the back and a broader stripe down each side. The body appears hairless.

Loopers arch their backs as they crawl. Cabbage loopers usually have a narrow, white stripe along each side and several narrow lines down the back. Eggs are dome-shaped and laid on the undersurfaces of older leaves. Adult moths have brown, mottled forewings marked in the center with a small silver figure 8.

Corn earworm eggs are white when first laid, but soon develop a dark red or brown ring around the top. Before hatching they darken as the larvae develop inside. Deeper ridges and a more hemispherical shape distinguish corn earworm eggs from looper eggs. Larvae have discrete rows of tubercles with one or two protruding hairs along their backs. As larvae mature they develop distinct stripes, but the overall color is variable. Earworms often migrate into spinach from surrounding crops. Other common names for this pest are tomato fruitworm and cotton bollworm.

Cutworm larvae frequently roll into a C-shape when disturbed. Black cutworm larvae are greasy gray to brown with several black bumps or tubercles on each segment. They may tunnel beneath the soil dragging parts of plants with them. The variegated cutworm larva is from 1.5 to 2 inches long, yellow to brown, with a row of four to six dull, yellow or pink diamond-shaped spots down the back. The granulate cutworm varies in color, but is lighter than the black cutworm, and does not tunnel. Adult cutworm moths have dark gray or brown front wings with irregular spots or bands, and lighter hind wings.

Larvae of the western yellowstriped armyworm are almost black, with two prominent and many fine, bright yellow stripes on the side. At maturity, it is about 1.5 to 2 inches long. Eggs are laid in clusters and covered with a gray, cottony material. This insect is an occasional pest of spinach; however, because it usually develops higher population levels than beet armyworm when it does occur, it can cause greater crop damage in a shorter period of time.

DAMAGE

Caterpillars feed in the crown of the spinach plant and can severely stunt or kill seedlings. The potential for damage and contamination continue right up until harvest. In the San Joaquin Valley, fall populations are much more damaging than spring populations. Cutworms feed at or below ground level.

MANAGEMENT

Biological Control
Many natural enemies attack these caterpillars. Among the most common parasites are the wasps, Hyposoter exiguae and Chelonus insularis, and the tachinid fly, Lespesia archippivora. Viral diseases also kill significant numbers.

Cultural Control
Disc fields immediately following harvest to kill larvae and pupae. Destroy weeds along field borders.

Organically Acceptable Methods
Cultural and biological controls and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are acceptable for use on organically grown produce.

Monitoring and Treatment Decisions
Start monitoring before seedlings emerge by checking for eggs and young larvae in surrounding weeds. If populations are high on weeds, watch carefully for larvae on seedlings. Once seedlings emerge, check for egg masses and young larvae twice a week. Loopers, armyworms, corn earworms, cutworms, and other caterpillars can be assessed together. Most insecticides are more effective against young larvae than against eggs, so wait until the majority of eggs have hatched before treating. For beet armyworm control, the best time to apply insecticide is at dawn or dusk (twilight hours).

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, information related to natural enemies and honey bees, and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. BACILLUS THURINGIENSIS ssp. AIZAWAI#
  (Various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B1
  COMMENTS: A bacterial organism that causes disease in caterpillars. Use if loopers, beet armyworm, or western yellowstriped armyworm are present. It must be eaten by the caterpillar in order for it to paralyze their stomachs. Not harmful to natural enemies. Control for all species varies with caterpillar size, the younger the caterpillar, the easier it is to control with this product. Efficacy is increased if applied late in afternoon or evening.
  . . . or . . .
  BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (Various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: A bacterial organism that causes disease in caterpillars. Use if cutworms, corn earworm, or loopers are present. It must be eaten by the caterpillar in order for it to paralyze their stomachs. Not harmful to natural enemies. Control for all species varies with caterpillar size, the younger the caterpillar, the easier it is to control with this product. Efficacy is increased if applied late in afternoon or evening.
 
B. METHOMYL*
  (Lannate SP) 0.5 lb 48 7
  (Lannate LV) 1.5 pt 48 7
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Do not use if leafminers are a problem.
 
C. PERMETHRIN*
  (Ambush 25W) 6.4–12.8 oz 12 1
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not apply more than 1 lb a.i./acre/season. Do not graze treated areas or feed crop refuse to livestock. Do not use if leafminers are a problem.
 
D. SPINOSAD
  (Entrust)# 1–2.5 oz 4 1
  (Success) 3–8 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Must be ingested by caterpillars; provides relatively fast knockdown of populations. Most effective on armyworms when they are small. Do not apply more than 29 oz of Success/acre/crop or 9 oz of Entrust/acre/crop.
 
E. SPINETORAM
  (Radiant SC) 5–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
 
F. CHLORANTRANILIPROLE
  (Coragen) 3.5–5 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 28
 
G. THIODICARB*
  (Larvin 3.2) 16–30 oz 48 14
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Has limited contact activity that requires larvae to feed on treated foliage to be controlled. Use higher dosage rates for heavy infestations, large larvae, or dense foliage. Do not exceed 60 oz/acre/season.
 
H. ZETA-CYPERMETHRIN*
  (Mustang 1.5 EW) 2.4–4.3 oz 12 1
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Make applications at least 7 days apart and do not apply more than 0.3 lb a.i./acre/season.
 
I. METHOXYFENOZIDE
  (Intrepid 2F) 4–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: Apply at first sign of feeding damage. Avoid consecutive use on succeeding generations to reduce the potential for development of resistance. Do not apply more than 64 fl oz/acre/season.
 
J. DIAZINON*
  (Diazinon AG 500) 2–4 qt 24 14
  (Diazinon AG 600WBC) 51–102 oz 72 0
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: For cutworms broadcast insecticide just before planting and immediately incorporate. Avoid drift and tailwater runoff into surface waters.
 
** Mix with enough water to provide complete coverage
+ 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/.
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Spinach
UC ANR Publication 3467
Insects and Mites
S. T. Koike, UC Cooperative Extension, Monterey County
M. LeStrange, UC Cooperative Extension, Tulare County
Acknowledgements for contributions to Insects and Mites:
W. E. Chaney, UC Cooperative Extension, Monterey County

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