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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Silken nests made by larvae of the omnivorous leafroller, Platynota stultana, and their feeding damage on developing grape flowers.

Grape

Monitoring Caterpillars

(Reviewed 6/06, updated 10/08)

In this Guideline:

Grape leaffolder and western grapeleaf skeletonizer feed on foliage and heavy populations can lead to defoliation. Omnivorous leafroller and orange tortrix feed on leaves, flowers, and developing berries, but their primary damage is feeding on fruit which enables rot organisms to enter fruit.

Rapid shoot growth. Early in rapid shoot growth, start monitoring for webbing on leaves caused by omnivorous leafroller or orange tortrix to map out areas of concern for bloom monitoring. Unroll leaves with orange tortrix and look for larval parasitism. Check for leaves skeletonized by western grapeleaf skeletonizer.

Bloom. Plan to treat omnivorous leafroller, grape leaffolder, and western grapeleaf skeletonizer (also, orange tortrix in coastal regions), if they have been a problem in the past. If they haven't been a problem in the past, be sure to monitor flower clusters or leaves for the caterpillars and damage they cause in wine/raisin grapes or in table grapes, as described below, to determine the need for treatment.

After bloom. Monitor during the growing season in wine/raisin grapes or in table grapes, by examining fruit clusters for omnivorous leafroller and orange tortrix and leaves for grape leaffolder and western grape leaf skeletonizer, following the guidelines below. Treatment after veraison for omnivorous leafroller and orange tortrix is limited in effectiveness and not recommended. However, veraison monitoring for all these caterpillars will alert you to larval damage going into harvest and potential problems the following year.

Harvest. At harvest, check table grapes for damage by omnivorous leafroller and grape leafroller to assess this year's management program and to plan for next year.

HOW TO MONITOR

  • Monitor 20 vines weekly by looking at 5 vines in each quadrant of the vineyard.
  • On each vine, check for pests and the damage they cause by following the guidelines below.
  • Record results on a monitoring form and treat using the treatment thresholds below (example form—125 KB, PDF).
PROCEDURE AND TREATMENT THRESHOLDS
Caterpillar Procedure Treatment threshold

Omnivorous leafroller

  • Examine 10 flower/fruit clusters in the center of each of 20 vines, for a total of 200 clusters.
  • If you see webbing and frass, look for caterpillars. Note the number of clusters infested with omnivorous leafroller.
  • At bloom, treat if any larvae are found.
  • After bloom, treat if 2 or more clusters are infested.

Orange tortrix (Coastal regions only)

  • During bloom and after, examine 10 flower/fruit clusters in the center of each of 20 vines, for a total of 200 clusters.
  • If you see webbing and frass, look for caterpillars. Note the number of clusters infested with orange tortrix.
  • If you find an average of 0.5-1 larva/vine, treatment may be warranted if parasites are not present.

Grape leaffolder

  • Count the number of rolled leaves per vine.
  • Unroll leaves and look for both healthy and parasitized grape leaffolder larvae.
  • Treatment may be warranted if population levels are increasing. Treat before larvae roll leaves.

Western grapeleaf skeletonizer

  • Check for skeletonized leaves.
  • If present, look for caterpillars and evidence of granulosis virus. (See the western grapeleaf skeletonizer section for a description of virus infection.)
  • If larvae are found and no granulosis virus is evident, treat soon after bloom.

IMPORTANT LINKS

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
General Information
L. G. Varela (Crop Team Leader), UC IPM Program, Sonoma County
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
D. R. Haviland, UC IPM Program, Kern County
P. A. Phillips, UC IPM Program, Ventura County
R. J. Smith, UC Cooperative Extension Sonoma County
A. Shrestha, UC IPM Program, Kearney Agricultural Center, Parlier

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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