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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Adult western flower thrips.

Cucurbits

Thrips

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

(Reviewed 11/05, updated 6/08)

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.

DAMAGE

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.

MANAGEMENT

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/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
When choosing a pesticide, consider information relating to water quality and impact on natural enemies and honey bees.
 
A. SPINOSAD
  (Entrust)# 2–2.5 oz 4 3 (1–cucumbers)
  (Success) 6–8 fl oz 4 3 (1-cucumbers)
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Do not apply more than 0.45 lb a.i. spinosad/acre/season. Rotate with an insecticide that has a different mode of action.
 
B. SPINETORAM
  (Radiant) SC 5–10 fl oz 4 1–cucumbers
  MODE OF ACTION GROUP NUMBER1: 5   3–other cucurbits
 
C. DIAZINON*
  (Diazinon) 50W Label rates 24 see label
  (Diazinon) AG500 Label rates 24 see label
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Labeled for use on melons and watermelons only. Highly toxic to honey bees. Avoid drift and tailwater runoff into surface waters.
 
D. DIMETHOATE
  (Dimethoate) 2.67 EC Melons: 1.5 pt 48 3
    Watermelons: 0.75–1.5 pt 48 3
  (Dimethoate 400) 4EC 0.5–1 pt 48 3
  MODE OF ACTION GROUP NUMBER1: 1B
  Comments: Only labeled for use on melons and watermelons. Highly toxic to honey bees.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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). For additional information, see their Web site at http://www.irac-online.org/.
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
L. D. Godfrey, Entomology, UC Davis
C. G. Summers, Entomology, UC Davis/Kearney Agricultural Center, Parlier
J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
R. L. Coviello, UC Cooperative Extension, Fresno County
C. B. Fouche, UC Cooperative Extension, San Joaquin County
J. B. LeBoeuf, AgriData Sensing, Inc., Fresno
M. Murray, UC Cooperative Extension, Colusa/Glenn counties

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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