Description of the Pest
Female brown soft scales lay a few eggs at a time during summer. Eggs hatch almost immediately and crawlers start to feed. Young scales move around until they are about half grown. They have mottled, yellowish, rounded shells. The young molt twice and reach maturity on leaves or twigs; they rarely move onto fruit. There are three to five overlapping generations a year. Brown soft scale numbers are usually highest from mid-summer to early fall.
Citricola scale, another soft scale that is similar to brown soft scale, may be found infesting the same trees, but because brown soft scales have multiple overlapping generations, colonies of this pest contain multiple life stages.
Damage
Heavy feeding by the soft brown scale reduces tree vigor, kills twigs, and reduces yields. Sooty mold grows on excreted honeydew and may affect fruit grade. The honeydew also attracts ants, which interfere with the biological control of a number of pests.
Management
Management of brown soft scale focuses on preserving its natural enemies and controlling ants. Avoid the repeated use of broad-spectrum insecticides for other pests that disrupt the biological control of soft scales. Individual treatment of this scale is rarely necessary. If natural enemies do not control the scales, a spot treatment with an oil spray is usually sufficient. In areas with citricola scale or black scale, populations of brown soft scale may be beneficial if they are not too large because their generations overlap and provide parasites with susceptible life stages to attack throughout the year, thus allowing parasite numbers to increase to higher levels.
Biological Control
A complex of Metaphycus spp. parasites attack brown soft scale. The most common of these is M. angustifrons in Southern California. In addition, the lady beetles Rhyzobius (Lindorus) lophanthae, Chilocorus orbus, and C. cacti prey on brown soft scales. Ants will protect brown soft scale from parasitism and predation because they feed on the honeydew that soft scales produce. Maximizing parasitism by controlling and reducing ants is critical for brown soft scale control because pesticides are not very effective against this scale species.
Organically Acceptable Methods
Use biological control and organically approved oils, such PureSpray Green (NR 440), on an organically certified crop.
Monitoring and Treatment Decisions
Monitor brown soft scale from June through October when biological control may be disrupted. Check the level of parasitism by looking for parasite exit holes and for developing parasites within the scale body. Organophosphate and carbamate insecticides are not very effective in controlling this pest. Usually, reduction of these insecticides in combinations with ant control will resolve the brown soft scale problem.
| Common name | Amount to use | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (type of coverage)** | (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. | ||||
| A. | NARROW RANGE OIL (UR92%) | |||
| (415, 440) | 1.2–1.4% (TC) | See label | When dry | |
| . . . or . . . | ||||
| NARROW RANGE OIL (UR99%) | ||||
| (415, 435, 440, 455) | 1.2–1.4% (TC) | See label | When dry | |
| RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most | ||||
| PERSISTENCE: Pests: short; Natural enemies: short | ||||
| MODE OF ACTION: Contact including smothering effects. | ||||
| COMMENTS: To avoid phytotoxicity problems, see timings for California red scale. Apply higher rate of narrow range oil in July or August only. Narrow range 440 spray oil (or higher) is preferable in the Central Valley during warmer months because of greater persistence, but risk of phytotoxicity increases unless using products with 99% unsulfonated residues (UR). Caution: Serious hazards are associated with oil sprays to green lemons because of phytotoxicity after sweating; check label for preharvest interval. | ||||
| B. | CARBARYL* | |||
| (Sevin XLR Plus) | 3–5 qt/acre (TC) | See label | 5 | |
| RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most | ||||
| PERSISTENCE: Pests: long; Natural enemies: long | ||||
| MODE-OF-ACTION GROUP NUMBER1: 1A | ||||
| COMMENTS: For use on all varieties. May cause outbreaks of citrus red mite and citrus thrips. | ||||
| C. | CARBARYL* | |||
| (Sevin XLR Plus) | 3–5 qt/acre (TC) | See label | 5 | |
| RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most | ||||
| PERSISTENCE: Pests: long; Natural enemies: long | ||||
| MODE-OF-ACTION GROUP NUMBER1: 1A | ||||
| COMMENTS: For use on all varieties. May cause outbreaks of citrus red mite and citrus thrips. | ||||
| . . . PLUS . . . | ||||
| NARROW RANGE OIL | ||||
| (415) | 0.5–1.4% | See label | When dry | |
| RANGE OF ACTIVITY: Pests: broad (unprotected stages of insects and mites); Natural enemies: most | ||||
| PERSISTENCE: Pests: short; Natural enemies: short | ||||
| MODE OF ACTION: Contact including smothering and barrier effects. | ||||
| COMMENTS: For use on all varieties. Reducing the rate of carbaryl increases survival of natural enemies. Reducing the rate of the oil reduces the risk of phytotoxicity, especially in warmer growing areas of the state. Do not apply during bloom. May increase citrus red mite numbers. Caution: Serious hazards are associated with oil sprays to green lemons because of phytotoxicity after sweating; check label for preharvest interval for tank mixes, observe all directions for use on all labels, and employ the most restrictive limits and precautions. Never exceed the maximum a.i. on any label when tank mixing products that contain the same a.i. | ||||
| D. | MALATHION | |||
| (Malathion 8 Flowable) | 7.5 pt/acre (TC) | 72 (3 days) | 7 | |
| RANGE OF ACTIVITY: Pests: broad (many insects); Natural enemies: most | ||||
| PERSISTENCE: Pests: intermediate; Natural enemies: intermediate | ||||
| MODE-OF-ACTION GROUPNUMBER1: 1B | ||||
| COMMENTS: For use on all varieties. | ||||
| ** | LV - Low-volume uses 20 to 100 gal water/acre. |
| TC - Thorough coverage uses 750 to 2,000 gal water or more/acre, depending on tree size. | |
| ‡ | 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 (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). |