How to Manage Pests

UC Pest Management Guidelines



Scientific Names:
Western flower thrips: Frankliniella occidentalis and other species

(Reviewed 12/09, updated 12/09, pesticides updated 5/16)

In this Guideline:

Description of the Pests

Thrips are small, slender insects with mouthparts developed primarily for sucking and rasping. The adults measure about 0.04 inch (1 mm) in length and have two pairs of fringed wings, carried lengthwise over the back.


Western flower thrips is both a beneficial insect (it feeds on spider mites) and a pest (it can damage flowers and shoot tips during the early growth stages or occasionally, if populations are severe, immature fruit). Both the young and adults cause damage by rasping and puncturing surface cells. This results in a silvering, and sometimes deformation, of the leaves: edges of leaves tend to curl downward.


Discing weeds before they flower can lessen attraction of the field to thrips. Do not disc after weeds have flowered, as thrips will move to crop plants. Monitor with yellow or blue sticky traps placed in field from seedling through flowering period to determine the magnitude of the thrips population. Be sure to determine that thrips-related damage is occurring and consider treating only if the population is causing serious damage to shoot tips, flowers, or fruit. Unnecessary treatments can cause spider mite buildup.

Organically Acceptable Methods

Weed management and sprays of the Entrust formulation of spinosad are acceptable in an organically certified crop.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Not all registered pesticides are listed. Always read the label of the product being used.
(Radiant SC) 5–10 fl oz 4 1–cucumbers
MODE-OF-ACTION GROUP NUMBER1: 5 3–other cucurbits
(Entrust)# 2–2.5 oz 4 3 (1–cucumbers)
(Success) 6–8 fl oz 4 3 (1-cucumbers)
COMMENTS: Do not apply more than 0.45 lb a.i. spinosad/acre per season. Rotate with an insecticide that has a different mode of action.
(Lannate SP) 0.5–1 lb 48 See comments
(Lannate LV) 1.5–3 pt 48 See comments
COMMENTS: For use on cucumbers, melons and summer squash only. PHI is 1 day when 0.5 lb or less for 90SP or 1.5 pt or less for LV formulations is used; when more than 0.5 lb (90SP) or 1.5 pt (LV) is used, PHI is 3 days.
(Dimethoate) 2.67 EC Melons: 1.5 pt 48 3
Watermelons: 0.75–1.5 pt 48 3
(Dimethoate 400) 4EC Melons: 1 pt 48 3
Watermelons: 0.5–1 pt 48 3
COMMENTS: Only labeled for use on melons and watermelons. Highly toxic to honey bees.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
# Acceptable for use on organically grown produce.
1 Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
* Permit required from county agricultural commissioner for purchase or use.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445

Insects and Mites

E. T. Natwick, UC Cooperative Extension, Imperial County
J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
C. S. Stoddard, UC Cooperative Extension, Merced & Madera counties

Acknowledgment for contributions to Insects and Mites:
R. L. Coviello, UC Cooperative Extension, Fresno County
C. B. Fouche, UC Cooperative Extension, San Joaquin County
L. D. Godfrey, Entomology, UC Davis
J. B. LeBoeuf, AgiData Sensing, Inc., Fresno
M. Murray, UC Cooperative Extension, Colusa and Glenn counties
C. G. Summers, Entomology, UC Davis and Kearney Agricultural Center, Parlier

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