How to Manage Pests
UC Pest Management Guidelines
In this Guideline:
Western flower thrips adults are minute insects, about
0.03 inch long, with two pairs of fringed wings. The adult has three color forms
that vary in abundance depending on the time of year. There is a pale
form that is white and yellow, except for slight brown spots or blemishes
on the top of the abdomen; an intermediate color form with an orange thorax and
brown abdomen; and a dark form that
is dark brown. The intermediate form is present throughout the year, but in spring
the dark form predominates while the pale form is most abundant at other times
throughout the year.
First-instar nymphs are opaque or light yellow, turning to golden yellow
after the first molt. The nymphal stage lasts from 5
to 20 days.
Western flower thrips are attracted to the blossoms of apples as
well as orchard cover crops and weeds. The primary damage is from egg-laying
punctures in newly formed fruit, which typically occur before petal fall. The
egg-laying site develops into tiny russetted spot surrounded by an irregular
yellow patch known as a pansy
spot (as it resembles the shape of a pansy).
Granny Smith and other green varieties as well as Rome Beauty and McIntosh show
more damage from this pest.
Thrips are often attracted to weeds blooming on the orchard floor. To prevent
driving thrips into the trees, do not disc the cover crop when trees are in
bloom. Open, weedy land adjacent to orchards should be disced as early as
possible to prevent thrips development and migration of adults into orchards.
Organically Acceptable Methods
Cultural controls and sprays of the Entrust formulation of spinosad are
organically acceptable tools.
Monitoring and Management
Inspect for adult western flower
thrips at 10% bloom. If several thrips, on the average, can be dislodged onto a
sheet of paper by tapping individual flower clusters, a treatment may be needed
to prevent damage.
Harvest fruit sample. At harvest,
assess program by monitoring fruit in the bins for thrips damage. Sample 200
fruit per bin from 5 bins per orchard (or 20-acre block in large orchards).
|Amount to use
choosing a pesticide, consider information relating to impact
on natural enemies and honey bees and environmental impact. Not
all registered pesticides are listed. Always read label of product being
OF ACTION GROUP NUMBER1: 5
Control may be improved by addition of an adjuvant to the spray mixture. Do not apply more than 29 oz/acre/year of Success or 9 oz/acre/year of Entrust.
UC IPM Pest Management Guidelines: Apple
UC ANR Publication 3432
Insects and Mites
J. L. Caprile, UC Cooperative
Extension, Contra Costa County
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
P. M. Vossen, UC Cooperative Extension, Sonoma and Marin counties
W. W. Coates, UC Cooperative Extension, San Benito County
H. L. Andris, UC Cooperative Extension, Fresno County
L. G. Varela, UC IPM Program, Sonoma County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
C. Pickel, UC IPM Program, Sutter and Yuba counties
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