Description of the Pest
San Jose scale overwinters as partially mature nymphs on limbs and trunks. Crawlers first appear in late April and May, followed by continuous overlapping emergence from late June through December.
In spring, nymphs develop into winged male and non-mobile (sessile) female scale insects. Female scales have gray circular scale coverings. If the covering is removed, their lemon-yellow body can be seen. In May females produce live young. Crawlers are bright yellow and tiny (about the size of the sharp end of a pin), with well-developed eyes, antennae, and legs. After locating a feeding site, the crawlers settle, begin feeding, and lose their antennae, legs, and eyes, becoming immobile. They soon begin to secrete a waxy substance that covers the body. Initially the waxy covering is white (white cap), but turns darker later in the first instar (black cap). Male scales have a more elongated covering than the females; males molt four times, whereas females have a rounder cover and molt twice.
In California there are three to four overlapping generations each year.
Damage
San Jose scale is a major pest of prune. It can infest branches, shoots, leaves, and fruit. It is inconspicuous and not usually noticed until large numbers develop on limbs. Adults and nymphs suck plant juices, injecting a toxin causing considerable damage. Feeding scale produce red halos on new wood and fruit, with fruit damage appearing as fruit spotting. They can seriously weaken branches and main scaffold limbs, causing permanent injury to mature trees. Limbs supporting large populations often ooze gum and exhibit rough bark and die back. Dead leaves adhering to fruit spurs during dormant season indicate the presence of scale. If trees have received repeated aerial dormant applications, San Jose scale can increase on the undersurface of branches.
Management
San Jose scale has many natural enemies that can frequently keep the pest under control if not disrupted by application of broad-spectrum insecticides. The scale is monitored as part of the spur sample during the dormant season and with pheromone traps and sticky tape in spring.
Biological Control
(View photos of healthy and parasitized San Jose scale online.)
Natural enemies that feed on San Jose scale include two predatory beetles: the twicestabbed lady beetle, and another small beetleCybocephalus californicus. A number of small chalcid and aphelinid wasps, includingAphytis melinus and Encarsia (=Prospaltella) perniciosi, parasitize this scale. These predators and parasitoids reduce scale numbers, but broad-spectrum insecticides used during the growing season for other pests disrupt this natural control, and scale numbers can increase as a result. Low winter mortality of scale during mild winters can also contribute to increase of scale numbers. Pheromone traps for San Jose scale attract parasitoids and should be used to monitor for the potential for biological control.
Organically Acceptable Methods
Use mineral oil sprays and biological control in a certified organic crop.
Monitoring and Treatment Decisions
The best time to apply insecticide is during the delayed dormant season when low-to-moderate numbers can be managed with oil sprays, which don't kill the scale parasites, and excellent spray coverage can be most easily achieved.
Dormant or Delayed-Dormant Season
Monitor San Jose scale during the dormant season by collecting 100 spurs or shoots 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 this monitoring form (PDF).
| Threshold (% live scale) | Treatment |
|---|---|
| below 5% | no spray |
| 5–19% | oil at 4–6 gal/acre |
| 20% and over | oil with insect growth regulator or insecticide |
Growing Season
Monitoring with pheromone traps from late bloom to petal fall will help you keep track of the appearance and development of San Jose scale, the level of parasitism, and can help time insecticide applications. Pheromone-trap monitoring cannot determine if treatment is needed but, used with degree-days or stick-tape traps to trap the crawlers, it can help determine the best timing for an insecticide application. The need for treatment is better assessed during the dormant season (spur sampling). Delayed dormant sprays are the preferred timing for treatment.
If dormant or delayed dormant spray control is inadequate, or this spray is not applied, treatment is also effective when applied soon after the emergence of crawlers in May. Monitor scale by putting up pheromone traps around February 25 (see Pheromone Traps) and placing sticky tape in the trees in April. 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 parasitoids. Adult male scales can be distinguished from the parasites by the presence of a dark line across their thorax where the wings attach. Record results on a monitoring form.
When the traps begin to catch males consistently, start accumulating degree-days (DD) 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 degree-days.
Calculate degree-days for San Jose scale in prune for your location using the San Jose scale pest model or degree-day table. To learn more about using degree-days to time insecticide applications, watch the degree-days video.
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. Consider eliminating the oil in this spray to preserve parasitoids if these beneficial insects are active. Check for parasitoid activity in dormant spur samples and for adult parasitoid wasps in the pheromone traps set out for male scale.
Take a fruit damage sample in mid-July to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program. See Fruit Evaluation at Harvest. Record results on a monitoring form (PDF).
Dormant and Delayed-Dormant Sprays
Dormant or delayed-dormant applications of many pesticides applied within 48 hours prior to rain events carry increased risks of surface water contamination resulting from orchard runoff, especially when the ground is saturated. Follow the Dormant Insecticide Contamination Prevention regulations when applying during this time of the year. Be especially careful when applying pyrethroid (MOA 3A) or organophosphate (OP; MOA 1B) insecticides, because they are highly toxic to aquatic life.
Pesticide spray drift risk is highest during dormant or delayed dormant spray applications due to lack of leaves to slow the progress of spray through the canopy. Growers should consider using Gear Up, Throttle Down or other spray practice to reduce spray drift including low drift nozzles, reduced sprayer fan speeds and use of synchronized sprayers to restrict spray movement. Currently, spray drift from pyrethroid and, to a lesser degree, organophosphate pesticide applications are of major concern regarding spray drift impacting surface water quality.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(fish) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
Centaur WDG | Dormant or Delayed-Dormant | 1 |
16 |
34.5 oz | 12 | 14 | Tank mix with narrow range oil. Carefull... | narrow | low | high 13 | low | moderate to long | intermediate | low | high | low | intermediate | 12/2025 | ||
|
|
Diazinon AG500 | Dormant or Delayed-Dormant | 1 |
1B |
Label rates | 96 | 21 | Check with your packer about restriction... | broad | low | high | high | moderate to long | high | high | extra high | intermediate | high | 12/2025 | ||
|
|
Omni Supreme # | Dormant or Delayed-Dormant | 1 |
UNM |
4 gal | 12 | — | Cover all parts of the tree with narrow... | broad | low | low | low | none to short | very low | low | very low | very low | very low | 12/2025 | ||
|
|
Imidan 70-W | Dormant or Delayed-Dormant | 1 |
1B |
2.125–4.25 lb | See label | 7 | Check with your packer about restriction... | broad | high | high | high | moderate to long | intermediate | low | high | intermediate | high | 12/2025 | ||
|
|
Esteem 0.86 EC | Dormant or Delayed-Dormant | 1 |
7C |
13–16 fl oz | 12 | 14 | Tank mix with narrow range oil. Carefull... | narrow | low | high 13 | low | long | low | low | high | very low | very low | 12/2025 | ||
|
|
Seize 35 WP | Dormant or Delayed-Dormant | 1 |
7C |
4–5 oz | 12 | 14 | Tank mix with narrow range oil. Carefull... | narrow | low | high 13 | low | long | low | low | high | very low | very low | 12/2025 | ||
|
|
Centaur WDG | May (Second-Choice Timing) | 5 |
16 |
34.5 oz | 12 | 14 | Good coverage is essential for good cont... | narrow | low | high 13 | low | moderate to long | intermediate | low | high | low | intermediate | 12/2025 | ||
|
|
Omni Supreme # | May (Second-Choice Timing) | 5 |
UNM |
2% | 0 | — | Do not use narrow range oil within 30 da... | broad | low | low | low | none to short | very low | low | very low | very low | very low | 12/2025 | ||
|
|
Esteem 0.86 EC | May (Second-Choice Timing) | 5 |
7C |
13–16 fl oz | 12 | 14 | Apply when scale crawlers first emerge.... | narrow | low | high 13 | low | long | low | low | high | very low | very low | 12/2025 | ||
|
|
Seize 35 WP | May (Second-Choice Timing) | 5 |
7C |
4–5 oz | 12 | 14 | Apply when scale crawlers first emerge.... | narrow | low | high 13 | low | long | low | low | high | very low | very low | 12/2025 | ||
|
|
Movento | May (Second-Choice Timing) | 5 |
23 |
6–9 fl oz | 24 | 7 | Adjuvate improves leaf penetration. Do n... | narrow | low | low | low | short | low | very low | low | very low | low | 12/2025 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # a b Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 a b c d e f Kills lady beetles.
Important Links
- Degree-day calculator
- Degree-day table
- Final fruit damage evaluation form for caterpillars, scale, and aphids
- Dormant spur sampling form for San Jose scale, European fruit lecanium, aphids, and mites
- Sampling form for insects monitored using pheromone traps and degree-days
- Using degree-days to time insecticide applications
UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464
F.J.A. Niederholzer, UC Cooperative Extension Sutter/Yuba counties
Acknowledgement for Contributions to Invertebrates
W.O. Reil (emeritus), UC Cooperative Extension Solano and Yolo counties
C. Pickel (emeritus), UC IPM and UC Cooperative Extension Sutter and Yuba counties
W.H. Olson, UC Cooperative Extension Butte County
F.G. Zalom (emeritus), Entomology, UC Davis
R.P. Buchner (emeritus), UC Cooperative Extension Tehama County
R. Krueger, USDA, ARS, Riverside
