How to Manage Pests

UC Pest Management Guidelines

Prune

San Jose Scale

Scientific name: Diaspidiotus (=Quadraspidiotus) perniciosus

(Reviewed 6/06, updated 4/09)

In this Guideline:


DESCRIPTION OF THE PEST

San Jose scale, a major pest of fruit trees, is inconspicuous and usually not noticed until it builds up to large numbers on limbs. If trees have received repeated aerial dormant applications, they can build up on the undersurface of branches. Limbs with large scale populations often ooze gum and exhibit rough bark and dieback. Dead leaves adhering to fruit spurs during dormant season indicate the presence of scale. Partially mature nymphs overwinter on limbs and trunks. In spring, nymphs develop into winged male and sessile female scale insects. Female scales have gray circular scale coverings. If the covering is removed, the lemon yellow body beneath can be seen. In May females produce live young. The young crawlers settle on shoots, feed and become adults or overwinter as partially grown scales. In California there are four overlapping generations each year. Crawlers first appear in late April and May, followed by continuous overlapping emergence from late June through December.

DAMAGE

San Jose scale infest branches, shoots, leaves, and fruit. Adults and nymphs suck plant juices and cause considerable damage. They seriously weaken branches and main scaffold limbs, causing permanent injury to mature trees. Crawlers settling on fruit may cause fruit spotting.

MANAGEMENT

A number of natural enemies help keep San Jose scale populations suppressed. Dormant sprays are recommended to manage scale populations, followed by regular monitoring to see if populations are increasing and to assess the presence of biological control. Broad-spectrum pesticides applied during the summer often destroy natural enemy populations, resulting in increased scale infestations; avoid such treatments where possible.

Biological Control

Many parasites and predators feed on San Jose scale. These include Aphytis spp., Encarsia perniciosi, andlady beetles (Chilocorus orbus and Cybocephalus californicus). However, in situations where heavy scale populations exist, biological control will not prevent severe damage, so annual sprays are usually needed. Use San Jose scale pheromone traps to help monitor scale parasites during the growing season.

Organically Acceptable Methods

Oil sprays and biological control by native scale parasites are organically acceptable management tools.

Monitoring and Treatment Decisions
Dormant season

Monitor San Jose scale during the dormant season by collecting 100 spurs and examining them for live scale as well as for tiny emergence holes, which indicate parasite activity. For details on presence-absence monitoring, see DORMANT SPUR SAMPLING and the monitoring form (PDF).

Growing season

Monitoring from late bloom until petal fall will help you keep track of the appearance and development of scale populations as well as the level of parasitism (Aphytis and Encarsia) but does not tell you if treatment is needed. It mainly tells you how to time treatment for best control in spring using degree-days and pheromone traps to predict the crawler stage or sticky traps to trap the crawlers. Need for treatment is better assessed during the dormant season. Delayed dormant sprays are the preferred timing for treatment.

If inadequate control is achieved with the dormant spray or the dormant spray is not applied, treatment is also effective when applied soon after the emergence of crawlers in May. Monitor scales by putting up pheromone traps around February 25 and placing sticky tape in the trees in April. For more information see PHEROMONE TRAPS and record results on a monitoring form (PDF). Place pheromone traps well within the canopy to keep them out of the wind. San Jose scale traps will attract both male San Jose scales and scale parasites (Aphytis melinus and Enarsia perniciosi). Adult male scales can be distinguished from the parasites by the presence of a dark line across their thorax where the wings attach.

When the traps begin to catch males consistently, start accumulating degree-days using a 51°F lower threshold and a 90°F upper threshold. If it is needed, apply a treatment for crawlers 600 to 700 degree-days after you catch the first males. Be aware that the traps may fail to catch any adults if weather is cold, rainy, or windy. Total generation time for San Jose scale is 1050 DD.

If May sprays are required, use a high-volume (dilute) application at 400 gallons or more per acre for best coverage; do not use a low volume application.

Fruit damage sample

In mid-July, take a fruit damage sample to assess the overall effectiveness of the current year's IPM program and to determine next year's needs. For details, see FRUIT EVALUATION AT HARVEST. Record results on a monitoring form (PDF).

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 the 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.
 
DORMANT OR DELAYED DORMANT (Preferred timing)
 
A. METHIDATHION*
  (Supracide) 25WP 4 lb 1 lb 48 0
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Preferred material for heavy infestations. Apply before blossoms open, or injury may occur. Do not graze treated areas or feed cover crops grown in treated areas to livestock.
 
B. DORMANT OIL such as:
  DORMANT FLOWABLE EMULSION 6 gal 1.5 gal 4 0
  NARROW RANGE OIL 4 gal 1.5 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Oil applications at this time may cause some young shoots to burn or die back, especially in years when trees are water-stressed, or have recently been subjected to freezing temperatures or to dry winds. Dormant flowable emulsion is less likely to cause burn. The Moyer variety is highly susceptible to oil injury; delaying the oil spray until late Feb.to March 1 will reduce oil burn.
  . . . PLUS . . .
  PYRIPROXYFEN
  (Esteem) 0.86 EC 13–16 fl oz/acre 12 14
  (Seize) 35WP 4–5 oz/acre 12 14
  MODE OF ACTION GROUP NUMBER1: 7C
  COMMENTS: An insect growth regulator. Do not apply more than once per growing season. Good coverage is essential for good control. Preferred treatment of high populations of scale in an environmentally sound program. Use allowed under a supplemental label.
  . . . or . . .
  DIAZINON* 50WP 3 lb 1 lb 24 21
  4EC 3 pt 1 pt 24 21
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Resistance to diazinon has been a problem in some populations of San Jose scale. Levels in surface waters of this material that are high enough to be toxic to certain aquatic invertebrates have occurred following rains in Jan. and Feb.; avoid runoff into surface waters.
  . . . or . . .
  CHLORPYRIFOS*
  (Lorsban) 4EC 2 pt 0.5 pt 4 14
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Apply chlorpyrifos only during dormant or delayed dormant period and do not allow meat or dairy animals to graze in treated orchards. Resistance to chlorpyrifos has been a problem in some populations of San Jose scale. Levels in surface waters of this material that are high enough to be toxic to certain aquatic invertebrates have occurred following rains in Jan. and Feb.; avoid runoff into surface waters.
  . . . or . . .
  CARBARYL*
  (Sevin) 80 S 1 lb 12 1
  (Sevin) XLR PLUS 1 qt 12 1
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: If resistance to diazinon or chlorpyrifos has been a problem, carbaryl is a good alternative. The best time to apply this material is about 2–3 weeks before bloom. Because carbaryl is so toxic to honey bees, do not apply it when there is any bloom in the orchard or in neighboring orchards or other crops. The XLR PLUS formulation is less toxic to honey bees than the other formualtions when applied in the evening or early morning, or when bees are not foraging.
 
C. DORMANT OIL such as:
  DORMANT FLOWABLE EMULSION 6 gal 1–1.5 gal 4 0
  NARROW RANGE OIL# 4 gal 1.5 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Cover all parts of the tree. Will control low-to-moderate infestations. If this spray is aimed primarily at San Jose scale, apply it in early to mid-Jan. This is an option if bloom time treatments are to be used for control of caterpillars. Oil applications at this time may cause some young shoots to burn or die back, especially in years when trees are water-stressed, or have recently been subjected to freezing temperatures or to dry winds. Dormant flowable emulsion is less likely to cause burn. The Moyer variety is highly susceptible to oil injury; delaying the oil spray until late Feb.to March 1 will reduce oil burn. Not all oils are organically acceptable; be sure to check individual products.
 
MAY (Second choice treatment timing)
 
A. PYRIPROXYFEN
  (Esteem) 0.86 EC 13–16 fl oz/acre 12 14
  (Seize) 35WP 4–5 oz/acre 12 14
  MODE OF ACTION GROUP NUMBER1: 7C
  COMMENTS: An insect growth regulator. Do not apply more than once per growing season. Good coverage is essential for good control. Preferred treatment of high populations of scale in an environmentally sound program. Use allowed under a supplemental label.
 
B. NARROW RANGE OIL# 2% 4% 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Do not use within 30 days of sulfur or lime sulfur treatment or apply to water-stressed trees. Do not apply oil within 2 weeks of captan. Not all oils are organically acceptable; be sure to check individual products.
 
** 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.
* Permit required from county agricultural commissioner for purchase or use.
# 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/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464

Insects and Mites

  • C. Pickel, UC IPM Program, Sutter/Yuba counties
  • F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
  • W. H. Olson, UC Cooperative Extension, Butte County
  • F. G. Zalom, Entomology, UC Davis
  • R. P. Buchner, UC Cooperative Extension, Tehama County
  • W. H. Krueger, UC Cooperative Extension, Glenn County
Acknowledgment for contributions to Insects and Mites:
  • W. O. Reil, UC Cooperative Extension Solano/Yolo counties

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