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How to Manage Pests
UC Pest Management Guidelines
Strawberry
Western Flower Thrips
Scientific Name: Frankliniella occidentalis
(Reviewed 6/08,
updated 6/08)
In this Guideline:
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Western flower thrips are slender, very small insects, about 0.03
inch (0.8 mm) long when mature. Adults have feathery wings and vary in color
from yellow to dark brown; nymphs are white or yellowish with small dark eyes.
In spring, flower thrips populations build up on alfalfa, weeds, ice plant, and
other vegetation and move from these hosts when they are cut, stop flowering,
or dry up.
Strawberry plantations often have a mixed population of thrips
that includes a low percentage of the onion thrips, Thrips tabaci.
Thrips feeding on strawberry blossoms causes the stigmas and anthers
to turn brown and wither prematurely, but not before fertilization has
occurred. Although often numerous on berries when cat-facing occurs, western
flower thrips do not cause cat-facing, which is a result of lygus bug feeding
and possibly other factors. As fruit develops, thrips feeding may cause a
russeting (Type I bronzing)
of the fruit around the cap, but this injury is seldom economic. (Other types
of bronzing are associated with phytotoxicity from sulfur and other types of
sprays (Type II) and from plant physiological factors (Type III). The most
severe bronzing that covers the entire fruit is believed to have a
physiological cause that is associated with hot temperatures occurring from May
through July.)
Populations of the western flower thrips build up on a number of
crops and weeds. They may migrate into strawberries when other crops are
harvested, when second-year strawberries or other perennial hosts stop
flowering, or when weeds dry up in spring. Control is not usually necessary
because western flower thrips rarely cause economic damage at densities that
typically occur in strawberry fields. Sprays applied to control thrips disrupt
biological control of other pests such as twospotted spider mites, lygus bugs,
whiteflies, and other insects. In addition, because western flower thrips feed
on spider mite eggs, at low population levels they can be beneficial. If
treatment is necessary, choose the least disruptive insecticide to preserve
biological controls agents.
Biological Control
Naturally occurring minute
pirate bugs (Orius spp.) feed on
thrips. Orius are also
available commercially, but release rates and timing have not been determined.
Organically Acceptable Methods
Sprays of the Entrust formulation of spinosad are acceptable for use on
organically certified strawberries.
Monitoring
and Treatment Decisions
Consider treating only if populations reach 10 thrips per blossom
when flowers are shaken onto a flat surface and thrips counted. A better way to
sample thrips is to place randomly collected flower blossoms into a glass
container with several drops of either ethyl acetate or methyl isobutyl ketone
(or with a small amount of either of these materials soaked into cotton or
other absorbent material). After at least one-half hour, count the thrips by
removing the blossoms and shaking them onto black paper. Because more thrips
will be found with this method, the treatment threshold is greater than that
indicated for shaking flowers.
| Common name |
Amount/Acre |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
|
(hours) |
(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. Not all registered pesticides are listed. Always read label of product being used.
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| (Note: For increased efficacy, any of the first four insecticides can be
tank mixed with either Pyrenone or PyGanic (E or F below). For tank mixes,
observe all directions for use on all labels, and employ the most restrictive
limits and precautions. Never exceed the maximum a.i. on any label when tank
mixing products that contain the same a.i.)
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| A. |
SPINOSAD |
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(Entrust)# |
1.25–1.5 oz |
4 |
1 |
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(Success) |
6 fl oz |
4 |
1 |
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MODE OF ACTION GROUP NUMBER1: 5 |
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COMMENTS: Rotate to an insecticide with a different mode of
action after two successive applications. Can be toxic to some natural
enemies (e.g. predatory mites, syrphid fly larvae) when sprayed and shortly thereafter (8-24 hours). |
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| B. |
MALATHION |
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5EC |
2–3 pt |
12 |
3 |
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8E |
1.5–2 pt |
12 |
3 |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: Residual activity only about 1 week. |
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| C. |
NALED |
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(Dibrom) 8EC |
1 pt |
48 |
1 |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: Do not use when temperature exceeds 85°F. |
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| D. |
PYRETHRIN/PIPERONYL BUTOXIDE |
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(Pyrenone) |
Label rates |
12 |
0 |
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MODE OF ACTION GROUP NUMBER1: 3 and 27A |
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COMMENTS: Variable efficacy. Not as disruptive of natural enemies as some other options. |
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| E. |
PYRETHRIN# |
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(PyGanic) 1.4EC |
16–64 oz |
12 |
0 |
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MODE OF ACTION GROUP NUMBER1: 3 |
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COMMENTS: Apply in sufficient water for thorough coverage. |
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UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468
Insects and Mites
F. G. Zalom, Entomology, UC Davis
M. P. Bolda, UC Cooperative Extension Santa Cruz Co.
P. A. Phillips, UC IPM Program/UC Cooperative Extension Ventura Co.
Acknowledgment for contributions to the Insects and Mites:
N. C. Toscano, Entomology, UC Riverside
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