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How to Manage Pests
UC Pest Management Guidelines
Grape
Monitoring Caterpillars
(Reviewed 6/06,
updated 6/06)
In this Guideline:
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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.
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 as
described below to determine the need for treatment.
After bloom. Monitor during the growing season 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.
HOW TO MONITOR (View
photos of caterpillars and damage at bloom and veraison and
their natural
enemies.)
- 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
observations on a monitoring form , and treat using the treatment thresholds
below.
PROCEDURE AND TREATMENT THRESHOLDS
| Caterpillar |
Procedure |
Treatment threshold |
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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 (i.e. 1% or more) are infested. |
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(Coastal regions only)
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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.
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If you find an average of 0.5-1 larva/vine, treatment may be warranted if parasites are not present. |
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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 when larvae are young before they roll leaves around themselves. |
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Check for skeletonized leaves. If present,
look for caterpillars and evidence of granulosis virus (view photo). (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. |
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UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
General Information
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma Co.
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma Co.
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura Co.
D. R. Haviland, UC IPM Program, Kern Co.
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo Co.
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