Description of the Pest
The San Jose scale has no visible egg stage; scales emerge from under the edge of their mother's covering as nymphs. There are three stages during the first instar: the crawler, which is mobile and locates a feeding site; the white cap, which feeds and becomes covered with a waxy secretion; and the black cap, which is a darker, harder wax covering under which they may overwinter. The male scale will molt four times, and is elongate and black. The female molts twice, and is circular and gray. Males emerge as winged adults while the females remain wingless under the scale covering. There are three to four generations per season, taking about 7 to 8 weeks per generation.
Damage
Scales suck plant juices from twigs and limbs and inject a toxin, resulting in loss of tree vigor, growth, and productivity. They are found on wood with thin bark and fruit. A red halo is produced around a feeding site. Untreated infestations can kill a tree in 1 to 2 years.
Management
In cherries San Jose scale is rarely a problem in most growing areas; it can be an occasional pest, however, in the southern San Joaquin Valley. A number of natural enemies help keep San Jose scale populations suppressed.
Biological Control
A number of natural enemies help keep San Jose scale populations suppressed. Species of the parasitic wasps Encarsia (formerly Prospaltella) and Aphytis lay an egg under the scale cover. The parasite larva consumes the scale body, and the new adult parasite cuts a circular hole in the scale cover to emerge. Both larvae and adults of the twicestabbed lady beetle, Chilocorus orbus, and the small nitidulid beetle, Cybocephalus californicus, feed on scale crawlers and settled nymphs. Broad-spectrum pesticides applied during the summer may destroy natural enemy populations and result in increased scale infestations.
Organically Acceptable Methods
Oil sprays and biological control by native scale parasites are acceptable in organically managed orchards.
Monitoring and Treatment Decisions
Calculate degree-days for monitoring San Jose scale at your location. Learn to use degree-days to time insecticide applications.
Populations of San Jose scale can be controlled with oil in the dormant season. Additional pesticides are necessary only when populations are severe. Treat during delayed-dormant period if scale population or sooty mold was observed the previous year.
| Common name | Amount to use** | REI‡ | PHI‡ | ||
|---|---|---|---|---|---|
| (Example trade name) | (conc.) | (dilute) | (hours) | (days) | |
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used. | |||||
| DORMANCY OR DELAYED-DORMANCY | |||||
| A. | NARROW RANGE OIL# | Label rates | See label | 0 | |
| MODE OF ACTION: Contact including smothering and barrier effects. | |||||
| COMMENTS: For low to moderate populations. | |||||
| B. | NARROW RANGE OIL | Label rates | See label | 0 | |
| MODE OF ACTION: Contact including smothering and barrier effects. | |||||
| . . . PLUS (for severe populations). . . | |||||
| DIAZINON* | |||||
| (Diazinon 50W) | 1 1/4 lb/100 gal water | 96 (4 days) | 21 | ||
| MODE-OF-ACTION GROUP NUMBER1: 1B | |||||
| COMMENTS: Organophosphate insecticides used during delayed dormancy are very toxic to honey bees. Remove bees from orchard if cover crops or weeds are in bloom. Oil sprays may injure trees that are water stressed. It is advisable to postpone an oil application to water-stressed trees until winter rains have replenished soil water and the tree bark is noticeably moist. 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 January and February; avoid runoff into surface waters. | |||||
| . . . or . . . | |||||
| PYRIPROXYFEN | |||||
| (Seize 35WP) | 4–5 oz | 12 | 14 | ||
| MODE-OF-ACTION GROUP NUMBER1: 7C | |||||
| COMMENTS: An insect growth regulator that suppress egg hatch. Good coverage is essential for good control. | |||||
| ** | For concentrate applications, use the amount given in 80–100 gal water/acre, or lower if the label allows; for dilute applications, amount is per 100 gal water to be applied in 300–400 gal water/acre, according to label. |
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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. |
| 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). |