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How to Manage Pests

UC Pest Management Guidelines


Yellow Aphid Complex

Scientific names: Yellow pecan aphid: Monelliopsis pecanis
Black margined aphid: Monellia caryella

(Reviewed 2/07, updated 8/10)

In this Guideline:


Both the yellow pecan aphid and the black margined aphid are somewhat similar in appearance and cause similar types of damage. Both species are yellow with black markings. The amount of black pigmentation varies with stage of development and time of year, but in general increases from spring to fall. The cornicles on both species are reduced to pores. Except for the winged adults, yellow pecan aphids have long setae, or hairs, that tend to stand out from the body at 45 to nearly 90 degree angles, giving the aphids a pincushion look. In addition, yellow pecan aphids have red eyes. Black margined aphids have much shorter setae than yellow pecan aphids and the setae form less than a 45 degree angle with the body. There are multiple generations of both species each year; populations tend to peak in spring and again in fall.


Both species primarily feed on the underside of leaves. Black margined aphids feed on the underside of leaves on major leaflet veins while yellow pecan aphids feed on the network of small veins located throughout the leaf. They damage pecan trees by extracting large amounts of photosynthate and water from leaves, which impairs the growth of both shoots and roots. They also secrete large amounts of honeydew on to leaves, and the sooty mold that grows on the honeydew can reduce photosynthetic efficiency.


By choosing insecticides that preserve beneficial insects, aphid populations will decrease over time.

  • Before June 1: Treat if honeydew is accumulating.
  • June 1 to August 15: Treat if the total number of aphids exceeds an average of 20 per compound leaf.
  • August 15 to leaf fall: Treat if the total number of aphids exceeds an average of 10 per compound leaf.

Researchers have some evidence of resistance to imidacloprid in Texas and New Mexico.  Growers have observed what appears to be imidacloprid resistance in Arizona.

Common name Amount to Use** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, information relating to natural enemies and honey bees as well as the environmental impact. Not all registered pesticides are listed. Always read label of product being used.
NOTE: Yellow pecan aphid resistance to insecticides has been a problem in other pecan-growing states. Alternate insecticides with different mode of action Group numbers, and do not use each more than once a season.
  (Admire Pro) 7–14 fl oz 12 7
  COMMENTS: This formulation of imidacloprid must be applied preventively before monitoring indicates a need; use if aphids have been a chronic problem in past years.
B. DIMETHOATE E267 1 pt/acre 48 21
  COMMENTS: Ground application only.
  (Lorsban Advanced) 1–4 pt/acre 24 28
  COMMENTS: Use chlorpyrifos in combination with one of the other insecticides listed in this table. Avoid runoff and drift into surface waters.
D. NARROW RANGE OIL# Label rates 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Although research has not been done in pecans, in other tree crops oil is used to suppress populations of aphids, while preserving beneficials. In organic crops, check with certifier to determine which products are organically acceptable.
  (Thionex) 3EC 1 qt/100 gal 24 see comments
  COMMENTS: Do not apply after shuck split. Do not exceed two applications per year or 4 quarts per acre per year. Cannot be applied in any situation where run-off may occur; check with county agricultural commissioner. May not be effective in all areas because of resistance.
** For dilute applications mix with 330-400 gal water/acre; for concentrate application mix with at least 20 gal water/acre.
+ Restricted entry interval (R.E.I.) is the number of hours from treatment until the treated area can be safely entered without protective clothing. Preharvest entry interval (P.H.I.) is the number of days from treatment to harvest. In some cases the R.E.I. exceeds the P.H.I. The longer of these 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: Pecan
UC ANR Publication 3456
R. Heerema, Extension Plant Sciences, New Mexico State University
C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter/Yuba counties
R. A. Van Steenwyk, Environmental Science, Policy, and Management, UC Berkeley
Acknowledgment for contributions to Insects:
G. S. Sibbett, UC Cooperative Extension, Tulare County

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