Description of the Pest
Woolly apple aphids infest roots, trunks, limbs, shoots, and occasionally fruit of apple trees. The bodies of these bark-feeding aphids are completely covered by masses of white, wool-like, waxy materials. This aphid is found in colonies on the aerial portions of the tree and on roots during winter. The nymphs migrate up or down the trunk of infested trees during summer and fall.
Damage
The main injury to young and mature trees is stunting due to the formation of root galls. If populations are high, honeydew and sooty mold will also be problems, and aphids may enter the calyx end of fruit.
Management
Woolly apple aphid is found throughout California's apple-growing regions, and it is a major pest in coastal counties. It occasionally infests pyracantha, hawthorn, and pear.
Resistant Varieties/Rootstocks
Winter Banana is one of the most susceptible varieties to aerial galls. Yellow Newtown fruit frequently has aphids in the calyx end. The Malling series of rootstock numbers 106 and 111 are resistant to this pest.
Biological Control
Aphelinus mali is a parasite that can completely control aerial colonies. In the absence of this parasite there can be large increases of aerial colonies and woolly aphids may be found in the calyx of the apple. Outbreaks of woolly apple aphid are most common following the use of pyrethroids, which destroys its natural enemies.
Organically Acceptable Methods
Resistant varieties and rootstocks as well as biological control are organically acceptable methods.
Treatment Decisions
The delayed dormant application should control woolly apple aphids. A summer application (late July to August) will only be required if the parasites are disrupted. Foliage treatments may be necessary for young trees with severe infestations.
| Common name | Amount per acre** | 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. | |||||
| FOLIAGE SPRAY | |||||
| A. | SPIROTETRAMAT | ||||
| (Movento) | 6–9 fl oz | 24 | 7 | ||
| MODE-OF-ACTION GROUP NUMBER1: 23 | |||||
| COMMENTS: Do not apply until after petal fall. Applications should be made before green tissue has hardened off. Allow 14 days between applications. Maximum is 25 fl oz/acre (0.4 lb a.i./acre) per crop per season. | |||||
| B. | BUPROFEZIN | ||||
| (Centaur WDG) | 34.5 oz | 12 | 14 | ||
| MODE-OF-ACTION GROUP NUMBER1: 16 | |||||
| COMMENTS: Centaur is an insect growth regulator; best used when crawlers are present. | |||||
| C. | DIAZINON* | ||||
| (Diazinon 50W) | 4 lb | 1 lb | 96 (4 days) | 21 | |
| MODE-OF-ACTION GROUP NUMBER1: 1B | |||||
| COMMENTS: Applications made during the foliage season are very disruptive to beneficials. Avoid drift and runoff into surface waters or choose alternative materials. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. | |||||
| ** | For dilute application, rate is per 100 gal water to be applied in 300 to 500 gal water/acre, according to label; for concentrate applications, use 80 to 100 gal water/acre or lower if the label allows. |
| ‡ | 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). |