How to Manage Pests

UC Pest Management Guidelines

Alfalfa

Thrips

Scientific Names:
Bean thrips: Caliothrips fasciatus
Onion thrips: Thrips tabaci
Western flower thrips: Frankliniella occidentalis

(Reviewed 11/06, updated 11/06)

In this Guideline:


DESCRIPTION OF THE PESTS

Thrips are minute, slender-bodied insects usually possessing two pairs of long, narrow wings, the margins of which are fringed with long hairs. Some species cause injury by direct feeding, others by vectoring plant viruses, and still others are predatory on mites and small insects. Because of their high populations in alfalfa and their easily identifiable injury some have long considered thrips to be major alfalfa pests.

DAMAGE

Thrips mouthparts form a lacerating-sucking cone, and the insects feed by rasping and lacerating the food tissues and then sucking-up the resulting juices. The rasping leads to deformed and crinkled leaves resulting from uneven growth around the injury (feeding) site. Feeding, particularly near the leaf mid-rib, causes curling and distortion of the leaves, which often have a cuplike or puckered appearance.

MANAGEMENT

Western flower thrips have never been shown to cause economic damage in California. In fact, they often serve as alternate prey for a number of natural enemy species commonly found in alfalfa. Western flower thrips can be an effective natural enemy of spider mites. The cost of treatment (insecticide and application costs) is not justified for this species. In addition, disruption to natural enemy populations and the potential outbreak of other pests caused by insecticide treatment must be taken into account.

The exceptions to the "do not treat thrips" recommendation in alfalfa include the following: 1) very high populations of bean thrips and/or onion thrips. These species are relative newcomers to alfalfa and are considerably more destructive than flower thrips. 2) dryland alfalfa may be considerably more susceptible to thrips injury than irrigated alfalfa.

Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness, taking into account efficacy and impact on natural enemies and honey bees. When choosing a pesticide, also consider environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. METHOMYL*
  (Lannate) LV Label rates 48 7
  (Lannate) SP Label rates 48 0
  MODE OF ACTION: A carbamate (Group 1A)1 insecticide.
  COMMENTS: Restricted re-entry interval: 48 hours. Do not graze or feed livestock for 7 days after application. Do not apply when bees are present or apply more than 3.6 lb a.i./acre/season.
 
B. PERMETHRIN*
  (Pounce) 3.2 EC Label rates 12 see comments
  MODE OF ACTION: A pyrethroid (Group 3)1 insecticide.
  COMMENTS: Do not use more than 0.2 lb a.i./cutting. Do not apply to mixed stands with intentionally grown forage grasses and/or legumes. Preharvest interval is 0 days for 4 oz/acre and 14 days for more than 4oz/acre.
 
 
**  See label for dilution rates.
+ 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 until the field can be grazed or cut. In some cases the R.E.I. exceeds the P.H.I.; the longer of these two intervals is the minimum time that must elapse before harvest may take place.
* Permit required from county agricultural commissioner for purchase or use.
1 Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430

Insects and Mites

  • C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
  • L. D. Godfrey, Entomology, UC Davis
  • M. Rethwisch, UC Cooperative Extension, Riverside County (Blythe)
  • D. R. Haviland, UC Cooperative Extension, Kern County
  • P. B. Goodell, Entomology, Kearney Agricultural Center, Parlier
  • R. F. Long, UC Cooperative Extension, Yolo County

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