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How to Manage Pests
UC Pest Management Guidelines
Grape
Thrips
Scientific names:
Grape thrips: Drepanothrips reuteri
Western flower thrips: Frankliniella occidentalis and others
(Reviewed 6/06,
updated 6/06)
In this Guideline:
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Thrips are small insects, 0.04 inch long, with
distinctive feathery wings. Color varies from yellow to brown in color. Grape
thrips and western flower thrips are the most important species causing damage
on grapes. Both species may be found in most grape-growing areas. Grape thrips populations usually reach their greatest numbers in July; this coincides with peak vine
growth, and as vine growth slows, the numbers of thrips decreases. Western flower thrips
populations peak in May, coinciding with grape bloom and the drying up of winter plant
hosts.
Table grapes are susceptible to fruit damage caused by the western
flower thrips. They create halo-spotting on
the fruit when they oviposit in berries during bloom and up to fruit set or
shortly thereafter. Both western flower thrips and grape thrips can scar berries with their feeding, which renders certain white varieties used for table grapes
unmarketable. Thrips scarring is primarily a problem on Red Globe, Calmeria,
Italia, and occasionally on Thompson Seedless. Fruit feeding discontinues in
summer when both species feed on new
vegetative growth.
In the North Coast, western flower thrips can feed in emerging
shoots in early spring and stunt shoots and cause leaves to cup, especially
during cool, rainy springs. Grape thrips may attack shoot tips in late spring
or early summer although damage does not become apparent until the population has already decreased. While
summer damage of leaves by thrips is common, it is not considered a problem for
most varieties. However, a heavy grape thrips population can be a problem in
Salvadors.
In general, thrips, are a minor problem on wine and raisin grapes in
California with the exception of large populations on emerging shoots in
cool-growing regions; however, table grapes are susceptible to thrips damage
and may require treatment.
Biological Control
Little is known about natural control of
thrips in vineyards but predators such as minute pirate bugs undoubtedly play a role in keeping populations in check.
Cultural Control
Avoid mowing cover crops infested with
thrips at budbreak or before bloom because thrips may move to vines and cause shoot stunting.
Organically Acceptable Methods
Biological and cultural controls and
sprays of the Entrust formulation of spinosad are acceptable in organically
managed vineyards.
Monitoring and Treatment
Decisions
On cool days after budbreak monitor for
thrips. Open shoots or gently tap buds over white paper to check for thrips.
Table grapes. During the
period of rapid shoot growth, inspect flowers or fruit clusters for adults or
larvae, as well as the predatory minute pirate bug, by striking clusters three
times over a white piece of cardboard. Normal population levels of western
flower thrips range from 5 to 25 adults and 10-50 larvae per cluster. High levels exceed 150 adults and 300
larvae per cluster. Damaging
population levels for grape thrips in clusters has not been determined. Bloom sprays may be necessary to
prevent berry scarring in table grape vineyards.
Wine grapes. Begin
monitoring after budbreak. Inspect new shoots in spring, especially in cool
regions, for shoot scarring and distorted leaves. In these areas treatment may
be necessary if damage increases and cool temperatures persist. Record
observations on a monitoring form .
| Common name |
Amount/Acre** |
P.H.I.+ |
| (trade name) |
|
(days) |
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| 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.
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| A. |
SPINOSAD |
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(Entrust)# |
1.25–2.5 oz |
7 |
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(Success) |
4–8 |
7 |
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MODE OF ACTION: A microbial (Group 5)1 insecticide. |
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COMMENTS: Restricted entry interval: 4 hours. Apply when eggs
first hatch to target the young larvae. Heavy infestations require a second application in 4 or 5 days. |
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| B. |
IMIDACLOPRID |
| |
(Provado Solupak) 75WP |
0.75–1 oz |
0 |
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MODE OF ACTION: A neonicotinoid (Group 4A)1
insecticide.
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COMMENTS: Restricted entry interval: 12 hours. Foliar
application: allow at least 14 days between applications. Do not exceed 0.5
lb a.i. of imidacloprid/acre/year. Repeat applications of any neonicotinoid insecticide (acetamiprid-Assail;
imidacloprid-Admire, Provado) can lead to resistance to all neonicotinoids. Alternate neonicotinoids with an
insecticide that has a different mode of action to help delay the development of resistance. |
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| C. |
DIMETHOATE 25WP |
6–8 lb |
28 |
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MODE OF ACTION: An organophosphate (Group 1B)1
insecticide.
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COMMENTS: Restricted entry interval: 2 days. Lower than label
rates can be used in early season when vine canopy is not dense. To avoid
visible deposit on berries, do not apply after berries reach 0.25 inch
diameter. Moderately disruptive to beneficials. Resistance may be a problem in some populations. |
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| D. |
METHOMYL* |
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(Lannate) LV |
0.75–1.5 qt |
Raisin/Table: 1 |
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(Lannate) 90SP |
0.5–1 lb |
Wine: 14 |
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MODE OF ACTION: A carbamate (Group 1A)1
insecticide.
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COMMENTS: Restricted entry interval: Check with county
agricultural commissioner. Do not feed treated grapes to livestock.
Disruptive to predators of mites and parasites of leafhoppers. Short lived, may not provide long enough control. |
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| E. |
NARROW RANGE OIL# |
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(JMS Organic Stylet Oil) |
1–2 gal |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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COMMENTS: Apply early in the season (from 1-inch shoot length
until set) for thrips control. Will help prevent shoot damage in early spring
but not effective for berry scarring. Commonly used when shoot growth is
slowed by cool spring temperatures. (Also controls mites and serves as a
contact treatment for powdery mildew in spring.) Using ground equipment,
spray for optimum coverage of leaf surfaces. Repeat sprays every 1–14 days.
Late season applications may leave a residue on post-veraison berries. Do not
apply with copper when fruit is present; do not apply within 10 days of sulfur. Read label carefully for other use restrictions. |
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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 the insects and mites section:
J. Granett, Entomology, UC Davis
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