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UC Pest Management Guidelines


Diamondback moth larva.

Cole Crops

Diamondback Moth

Scientific Name: Plutella xylostella

(Reviewed 6/07, updated 10/10)

In this Guideline:


DESCRIPTION OF THE PEST

Diamondback larvae are small (about 0.33 inch when full grown) compared to other caterpillars in cole crops. The larval body is wider in the middle and tapering at both ends with two prolegs on the last segment forming a distinctive V-shape at the rear end. When disturbed the larvae wiggle frantically or rapidly attach a silken line to a leaf and drop over the edge. They feed mostly on outer or older leaves of older plants chewing out small holes or at the growing points of young plants. They will also feed on floral stalks and flower buds. Larvae mature in 10 to 14 days and spin a loose cocoon on leaves or stems for pupation. Adult moths lay their tiny, roundish eggs singly on the undersides of leaves; eggs are difficult to find. Although they may occur all year round, especially in coastal areas, diamondback moths are often abundant in spring and early summer, and populations may rise again in fall.

DAMAGE

Diamondback moth infestations are most serious when they damage the crowns or growing points of young plants or Brussels sprouts. This injury can severely stunt growth. Sometimes diamondback moth caterpillars may also bore into heads of broccoli or cauliflower, or in the flower buds of stalks, causing economic injury and contamination. Injury to leaves is not usually serious, except when the wrapper or cap leaves of cabbage are injured.

MANAGEMENT

Natural enemies and insecticides applied to control other pests keep the diamondback moth under satisfactory control in most fields in California, but keep records of diamondback moth as you monitor for other caterpillars.

Biological Control
Natural enemies often effectively control diamondback moth in California. In southern California, the ichneumonid wasp, Diadegma insularis, has been identified as the most common parasite. Trichogramma pretiosum may also attack diamondback eggs. Various predators such as ground beetles, true bugs, syrphid fly larvae, and spiders can be important factors in controlling populations. Microbial diseases are not known to be a significant mortality factor.

Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable management tools.

Monitoring and Treatment Decisions
Check fields during the seedling stage, at thinning, and just before heading. Also, record diamondback larvae numbers when you make your twice-weekly samples for other caterpillar pests. In cabbage fields, regularly monitor wrapper leaves for damage after heading. Adult moths frequently migrate from fields being harvested or disced under, so carefully check border rows if populations were high in adjacent fields. No treatment levels have been developed for diamondback moth in California; however, treatment may be required if significant injury to growing points is occurring.

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. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
 
B. DIAZINON*
  (Diazinon) 50W 0.5–1 lb 4 days 0
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Avoid drift and tailwater runoff into surface waters.
 
C. EMAMECTIN BENZOATE*
  (Proclaim) 3.2–4.8 oz 12 14
  MODE OF ACTION GROUP NUMBER1: 6
 
D. INDOXACARB
  (Avaunt) 2.5–3.5 oz 12 3
  MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Do not apply more than 14 oz/acre/crop. Add a wetting agent to improve coverage. Minimum interval between sprays is 3 days.
 
E. SPINETORAM
  (Radiant) SC 5–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Toxic against some natural enemies (predatory thrips, syrphid fly larva, beetles) when sprayed and 5 to 7 days after. Control improved with addition of an adjuvant.
 
F. SPINOSAD
  (Entrust)# 0.5–1.25 oz 4 1
  (Success) 6 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Toxic against some natural enemies (predatory thrips, syrphid fly larva, beetles) when sprayed and 5 to 7 days after.
 
G. CHLORANTRANILIPROLE
  (Coragen) 3.5–5 fl oz 4 3
  MODE OF ACTION GROUP NUMBER1: 28
  COMMENTS: Foliar application; use with an effective adjuvant for best performance.
 
H. FLUBENDIAMIDE
  (Synapse) WG 2 oz 12 1
  MODE OF ACTION GROUP NUMBER1: 28
  COMMENTS: Do not apply more than 4 oz/acre (0.06 lb a.i./acre)/crop season.
 
I. METHOXYFENOZIDE
  (Intrepid) 2F 8 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: For early-season applications only to young crop and small plants.
 
J. METHOMYL*
  (Lannate) LV 0.75–3 pt 48 see comments
  (Lannate) SP 0.25–1 lb 48 see comments
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Preharvest interval is 3 days for broccoli, Brussels sprouts, and cauliflower and 1 day for cabbage. See label for other cole crops.
 
+ 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.
# 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/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cole Crops
UC ANR Publication 3442
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgments for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
W. E. Chaney, UC Cooperative Extension, Monterey County
N. C. Toscano, Entomology, UC Riverside

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