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UC Pest Management Guidelines


Speckled green fruitworm larva feeding on leaf.

Plum

Green Fruitworms

Scientific names: Orthosia hibisci, Amphipyra pyramidoides, and others

(Reviewed 5/06, updated 4/09)

In this Guideline:


DESCRIPTION OF THE PESTS

Green fruitworms include several species of caterpillars, all of which are pale green, often with whitish stripes down each side of the body and a narrow stripe down the middle of the back. Most species pass the winter as pupae or adults, and have one generation each year.

DAMAGE

Green fruitworms eat large holes in young leaves and fruit during late bloom and petal fall causing fruit to be scarred and misshapen as they grow.

MANAGEMENT

Dormant treatments and bloomtime applications for other pests help keep fruitworm populations under control. However, regular monitoring each season is important so that prompt action can be taken if damaging populations develop.

Biological Control
Certain parasitic wasps (Apanteles, Eulophus, Meteorus, and Ophion spp.) help keep green fruitworm populations under control.

Organically Acceptable Methods
Biological control and Bacillus thuringiensis sprays and sprays of the Entrust formulation of spinosad are organically acceptable methods of controlling these pests.

Monitoring and Treatment Decisions
If treatment is necessary, treat at late bloom to petal fall when larvae are present. A treatment threshold of 1 worm per 100 fruit clusters per 20-acre block or 1 worm per 50 beat-tray samples has been developed for pears and probably is applicable to stone fruits. Bacillus thuringiensis formulations are safe to use during bloom and are effective on small larvae. If you use other materials, make applications during or shortly after petal fall. Spot-treat localized infestations. Continue to monitor for the pest after treatment. If no more young larvae are found, no more control actions are necessary for the season.

Common name Amount to Use** R.E.I.+ P.H.I.+
(trade name) (conc.) (dilute) (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, impact on natural enemies and honey bees, and impact of timing on beneficials. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: Most effective on small caterpillars. Does not destroy natural enemies. Make 2 applications during bloom: the first between popcorn and the beginning of bloom and the second 7–10 days later, but no later than petal fall. Compatible with fungicide sprays, and can be tank mixed with them. Good coverage is essential. Ground application using a concentrate rate (80–100 gal water maximum) is preferred. If aerial applications must be made because conditions do not permit ground application, a concentrate rate (5 gal or less) is preferred. Fly material on at a height of about 20 feet over the canopy using appropriate nozzles to allow better deposition on the tree tops.
 
B. SPINOSAD
  (Entrust)# 1.71–2.5 oz 0.43–0.6 oz 4 7
  (Success) 6–8 oz 1.5–2 oz 4 7
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Most effective when applied at petal fall; apply only during late evening, night, or early morning to avoid injury to honey bees. To avoid development of insect resistance, do not treat successive generations of the same pest with the same product.
 
** For dilute applications, rate is per 100 gal water to be applied in 300–500 gal water/acre, according to label; for concentrate applications, use 80–100 gal water/acre, or lower if the label allows.
+ 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.
Not recommended or not on label.
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/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Plum
UC ANR Publication 3462
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Insects and Mites:
R. E. Rice, Kearney Agricultural Center, Parlier

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