How to Manage Pests

UC Pest Management Guidelines

Walnut

San Jose Scale

Scientific Name: Diaspidiotus (=Quadraspidiotus) perniciosus

(Reviewed 12/07, updated 4/09)

In this Guideline:


DESCRIPTION OF THE PEST

Female San Jose scale give birth to living young that emerge from under the edge of the scale covering. These tiny yellow crawlers wander in a random fashion until they find a suitable place to settle. Immediately upon settling, the crawlers insert their mouthparts into the host plant and begin feeding and secreting a white waxy material (white cap stage); eventually the waxy covering turns black and is known as the black cap stage.

San Jose scales overwinter predominantly in the black cap stage, although in mild years some adult mated females may also survive. In late January, these nymphs resume their growth. Immature male and female scales are indistinguishable until the first molt. At this time, the male scale covering begins to elongate, while the female's remains circular. Males molt a total of four times. Following the final molt, adult male scales emerge from the scale covering as tiny, yellow winged insects. They mate with the females, who remain under the scale covering. After about two months, crawlers begin to emerge from the females, usually in April; peak emergence is generally in early May. There are usually four generations a year. Summer generations overlap and crawlers are present throughout summer and fall.

DAMAGE

Infested trees look water stressed, and fruiting wood encrusted with scale insects may die back. The infested bark often cracks and dies, and heavily-infested scaffold limbs and branches die within 1 to 2 years.

MANAGEMENT

In many orchards, San Jose scale is kept below damaging levels by natural enemies. High populations of this scale often result from the use of chemicals that are disruptive to parasites and predators; generally San Jose scale is not a pest in northern California. Where damaging populations do develop, the preferred method of control is to target the sensitive crawler stage with an oil spray during the growing season.

Biological Control
Many parasites and predators have been observed feeding on San Jose scale, including most of those listed for walnut scale. In undisturbed situations, these beneficials play a significant role in keeping San Jose scale populations below economic levels. However, in situations where heavy populations exist, these parasites and predators may not respond before severe damage occurs, so sprays may be needed.

Organically Acceptable Methods
Biological control and sprays of certain narrow range oils can be used in an organically certified crop.

Monitoring and Treatment Decisions
Monitor scales in the dormant period. For details on how to monitor San Jose scale with other pests, see DORMANT MONITORING. Examine scaffold limbs, branches, and prunings for the characteristic black caps and old scale bodies. Treatment is required when there are more than an average of 5 black caps per foot of last year's wood and less than 90% parasitism. If a population needs treatment, consider treating during delayed dormancy to achieve best coverage and control and to avoid killing natural enemies.

Oils are good choices in an IPM program because they do not cause water quality problems, but to avoid injuring walnut trees, only apply oils during the growing season. If the walnut aphid parasite, Trioxys pallidus, is active, however, oil is not recommended because it will kill Trioxys. Do not apply oils during dormancy or between bud break and shoot elongation because they can injure the tree. Organophosphate insecticides such as methidathion and chlorpyrifos can be applied during dormancy but pose water quality problems where run-off is an issue. Pyriproxyfen (Seize) may be applied during dormancy (without oil) and during delayed dormancy.

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 and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
CAUTION: Oils are not recommended for use during the dormant season on walnut trees.
         
A. METHIDATHION*      
  (Supracide) 25WP 8 lb 2 lb 3 days 7
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Do not combine with oil or severe phytotoxicity may occur. Do not graze livestock in treated orchard. Do not apply more than once during dormancy or twice during the growing season.
         
B. PYRIPROXYFEN      
  (Seize) 35WP 4–5oz 1–1.25 oz 12 21
  MODE OF ACTION GROUP NUMBER1: 7C
  COMMENTS: Do not exceed two applications/growing season or apply closer than 14 days apart. During the growing season, a nonionic surfactant may be added to increase efficiency. Apply concentrate applications in a minimum of 100 gal/water/acre. Timing of this product can be adjusted to provide some early season control of codling moth.
         
C. CHLORPYRIFOS*      
  (Lorsban) 4EC 4 pt 1 pt 24 14
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Make no more than 2 applications/season. Levels in surface waters of this material that are high enough to be toxic to certain aquatic invertebrates have occurred following rains; avoid runoff into surface waters.
         
D. NARROW RANGE OIL# Label rates 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: An option primarily for organic growers; oil is destructive to the walnut aphid parasite, Trioxys pallidus. Apply as a dilute application in at least 300 gal/acre if applied in the delayed dormant period. An application in summer will suppress low to moderate populations. In most areas, oils can be applied in summer. However to avoid injury, the trees must not have suffered from a lack of adequate soil moisture or other stressing factor (insects, disease damage, etc.) at any time during the year and the temperature must not exceed 90°F at or shortly after time of application. Do not apply after husk split. If in doubt, check with your farm advisor. In any case, do not apply oils to walnuts during the dormant season or between bud break and shoot elongation. Check with certifier to determine which products are organically acceptable.
   
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/.
** For concentrate application, use the amount given in 80–100 gal water/acre, or lower if the label allows; for dilute application, amount is per 100 gal water to be applied in 300–500 gal water/acre, according to label.
+ 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 these two intervals is the minimum time that must elapse before harvest may occur.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown crops.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471

Insects and Mites

  • C. Pickel, UC IPM Program/UC Cooperative Extension, Sutter/Yuba counties
  • J. A. Grant, UC Cooperative Extension, San Joaquin County
  • W. J. Bentley, UC IPM Program/Kearney Agricultural Center, Parlier
  • J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
  • W. W. Coates, UC Cooperative Extension, San Benito County
  • R. A. Van Steenwyk, Insect Biology, UC Berkeley
Acknowledgment for contributions to Insects and Mites:
  • W. H. Olson, UC Cooperative Extension, Butte County
  • L. C. Hendricks, UC Cooperative Extension, Merced County
  • G. S. Sibbett, UC Cooperative Extension, Tulare County

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