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How to Manage Pests

UC Pest Management Guidelines

Aerial colony of woolly apple aphids.


Woolly Apple Aphid

Scientific name: Eriosoma lanigerum

(Reviewed 8/06, updated 1/11)

In this Guideline:


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.


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.


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 to use** R.E.I.+ P.H.I.+
(trade name) (conc.) (dilute) (hours) (days)

Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to impact on natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
DELAYED DORMANT (Preferred timing)
A. NARROW RANGE OIL Label rates Label rates see label 0
  MODE OF ACTION: Improves translaminar movement and insecticide persistence.
  . . . PLUS . . .
  (Lorsban) 4EC Label rates 4 0
  COMMENTS: Avoid drift and runoff into surface waters or choose alternative materials. Chlorpyrifos has been found in surface waters at levels that violate federal and state water quality standards.
  . . . or . . .
  DIAZINON* 50WP 2–4 lb 0.5–1.0 lb 4 days 21
  COMMENTS: Avoid drift and runoff into surface waters or choose alternative materials. Diazinon has been found in surface waters at levels that violate federal and state water quality standards.
  (Movento) 6–9 fl oz 24 7
  COMMENTS: Do not apply until after petal fall. Allow 14 days between applications. Maximum is 25 fl oz/acre (0.4 lb a.i./acre)/crop/season.
B. DIAZINON* 50WP 4 lb 1 lb 4 days 21
  MODE OF ACTION: An organophosphate (Group 1B)1 insecticide.
  COMMENTS: Applications made during the foliage season are very disruptive to beneficials. Avoid drift and runoff into surface waters or choose alternative materials.
** For dilute application, rate is per 100 gal water to be applied in 300–500 gal water/acre, according to label; for concentrate applications, use 80–100 gal water/acre or lower if the label allows.
+ 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 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). For additional information, see their Web site at http://www.irac-online.org/.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Apple
UC ANR Publication 3432
Insects and Mites

  • J. L. Caprile, UC Cooperative Extension, Contra Costa County
  • L. R. Wunderlich, UC Cooperative Extension, El Dorado County
  • P. M. Vossen, UC Cooperative Extension, Sonoma and Marin counties
  • W. W. Coates, UC Cooperative Extension, San Benito County
  • H. L. Andris, UC Cooperative Extension, Fresno County
  • L. G. Varela, UC IPM Program, Sonoma County
  • W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
  • C. Pickel, UC IPM Program, Sutter and Yuba counties

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