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UC Pest Management Guidelines


Fifth-instar larvae of the western grapeleaf skeletonizer, Harrisina brillians.

Grape

Western Grapeleaf Skeletonizer

Scientific name: Harrisina brillians

(Reviewed 6/06, updated 10/08)

In this Guideline:


DESCRIPTION OF THE PEST

The metallic bluish or greenish black western grapeleaf skeletonizer moths fly during the day. Body length is about 0.6 inch and the wing span is 1 to 1.3 inches. There are three generations per year in the Central Valley and two generations in the cooler coastal regions. Adults of the first generation in the Central Valley emerge from hibernating pupa in early spring to June. The pale yellow or whitish capsule-shaped eggs are laid in clusters on the underside of grape leaves. After hatching, the larvae line up and feed side-by-side on the leaf underside until the early fourth instar stages. There are five larval stages. The first two stages are cream colored, the third stage is brownish, and the fourth and fifth stages are yellow with two purple and several blackish bands. Larvae have conspicuous tufts of long black poisonous spines that cause skin welts on field workers. The fifth or last larval stage is about 0.6 inch long. When mature, larvae crawl under the loose bark or into ground litter and spin a dirty, whitish cocoon to pupate.

DAMAGE

First through the early fourth instar larvae feed on the lower leaf surface, leaving only the veins and upper cuticle. This gives leaves a whitish paperlike appearance; eventually the entire leaf turns brown. The late fourth and all fifth stage larvae skeletonize the leaves, leaving only the larger veins. When abundant, larvae can defoliate vines by July. When vines are severely defoliated, larvae will then feed on grape clusters, which can result in bunch rot. Defoliation can also result in sunburn of the fruit and loss of quality. Defoliation after harvest may weaken vines by affecting stored reserves. Larvae also can cause problems for workers at harvest because hairs on their bodies can irritate the skin if they are brushed against.

MANAGEMENT

Western grape leaf skeletonizer does not occur in all grape-production areas because the moths are not long-distance fliers and this pest has been slow to spread in California since its first appearance in the 1940s. In areas where it does occur, granulosis virus usually keeps populations below economically damaging levels. When the virus is insufficient, western grapeleaf skeletonizer is easily controlled with insecticides that are also effective on other caterpillars, leafhoppers, or thrips.

Biological Control
Two insect parasites, Apanteles harrisinae and Amedoria misella (Sturmia harrisinae), attack western grapeleaf skeletonizer larvae. Thousands of these parasites have been released in the San Joaquin Valley, and Amedoria misella is common in many vineyards in the San Joaquin Valley.

A granulosis virus, endemic in southern California, has been introduced in selected areas with excellent success. It is extremely infectious when it is introduced into an outbreak population of western grapeleaf skeletonizer. Symptoms of populations infected with the virus include: (1) eggs within clusters are scattered instead of compactly laid, and the number of eggs is reduced; (2) most eggs fail to hatch; (3) larvae consume tiny patches of tissue rather than consuming entire areas of the leaf; (4) diseased larvae are sluggish and feed solitarily instead of in tight groups and usually tend to wander irregularly, leaving a visible trail of liquid excrement; and (5) larval growth and coloration change, and larvae shrink and eventually die. This virus is transmitted from one generation to the next by disease-carrying adults that survive a low degree of infection in the larval stage.

Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for organically certified grapes.

Monitoring and Treatment Decisions
If the granulosis virus is not present, the amount of leaf damage will increase with each generation. Monitor end and border vines during the first generation. This can be done at bloom when monitoring for other caterpillars; see MONITORING CATERPILLARS. Record results on a monitoring form (example form125 KB, PDF). If larvae are found and the virus is not present, treat soon after bloom. If needed later in season, treat when young larvae are found.

Check table grapes for sunburned fruit, a possible sign of defoliation caused by western grape leaf skeletonizer.

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 and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. METHOXYFENOZIDE
  (Intrepid) 2F 10–16 fl oz 4 30
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: Do not apply more than 48 fl oz/acre/season.
 
B. SPINOSAD
  (Entrust)# 1.5–2.5 oz 4 7
  (Success) 4–8 oz 4 7
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Apply when eggs first hatch to target the young larvae. A stomach poison; most effective when ingested. Heavy infestations require a second application in 4 or 5 days. To protect honeybees, apply only during late evening, night, and early morning when bees are not present in the vineyard.
 
C. CRYOLITE
  (Kryocide) 96WP 6–8 lb 12 30
  (Prokil Cryolite) 96 6–8 lb 12 30
  MODE OF ACTION GROUP NUMBER1: 9A
  COMMENTS: Wine and Raisin: Limit of 2 applications/season. Table: One application only and not after fruit formation. If used on wine grapes or grapes that may be sold to a winery for export, observe their restrictions on applications. A stomach poison that must be consumed by larvae so thorough coverage is important. Less harmful to natural enemies than methomyl and carbaryl and provides long residual action.
 
D. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: Only effective against young larvae. Provides fairly good control, has a short residual life, and is not harmful to natural enemies. If coverage is not satisfactory or if all the eggs have not hatched, requires a second treatment.
 
E. ACETAMIPRID
  (Assail) 70WP 1.1 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 4A
 
F. ABAMECTIN*
  (Agri-Mek) 0.15%EC 8–16 fl oz 12 28
  MODE OF ACTION GROUP NUMBER1: 6
  COMMENTS: Do not make more than 2 applications/growing season. Dust on leaves will inhibit absorption of this material. Effectiveness is also reduced by sulfur burn on leaves.
 
G. IMIDACLOPRID
  (Provado Solupak) 75WP 1 oz 12 0
  MODE OF ACTION GROUP NUMBER1: 4A
  COMMENTS: Foliar application: allow at least 14 days between applications. Do not exceed 0.5 lb a.i. of imidacloprid/acre/year.
 
H. METHOMYL*
  (Lannate) LV 0.75–1.5 qt 7 days Raisin/Table: 1
  (Lannate) 90SP 0.5–1 lb 7 days Wine: 14
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Do not feed treated grapes to livestock. Disruptive to predators of mites and parasites of leafhoppers. Has a short residual life. When used for late-season leafhopper control, this material also controls skeletonizer larvae.
 
** Apply 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.
* 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/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma County
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura County
D. R. Haviland, UC IPM Program, Kern County
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo County
Acknowledgment for contributions to Insects and Mites:
J. Granett, Entomology, UC Davis

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