How to Manage Pests

UC Pest Management Guidelines

Pecan

Yellow Aphid Complex

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

(Reviewed 12/15, updated 12/15)

In this Guideline:


DESCRIPTION OF THE PESTS

The yellow pecan aphid and the black margined aphid are similar in appearance.

  • Both species are yellow with black markings. The amount of black pigmentation varies with the stage of development and the time of year, but in general it 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 (hairs) that tend to stand out from the body at 45- to nearly 90-degree angles, giving the aphids a pincushion look. In contrast, black margined aphids have much shorter setae and they form less than a 45-degree angle with the body.
  • Yellow pecan aphids have red eyes.

There are multiple generations of both species each year. Numbers tend to peak in spring and again in fall.

DAMAGE

The yellow pecan aphid and black margined aphid cause similar types of damage. They are significant pests of pecan in California and can dramatically impact production and nut quality.

Both species feed primarily on the underside of leaves. Black margined aphids feed 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 shoots and roots. They also secrete large amounts of honeydew onto leaves. The sooty mold that grows on the honeydew can reduce photosynthetic efficiency.

MANAGEMENT

Monitor often since aphid numbers can increase rapidly and exceed economic thresholds quickly. Begin scouting for yellow pecan and black margined aphids in May and continue every 4 to 5 days throughout shoot and nut development. Look at the undersurface of 5 compound leaves on at least 10 random trees throughout the orchard for a total sample of at least 50 compound leaves.

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

Insecticides that preserve beneficial insects will decrease aphid populations over time.

Although imidacloprid is traditionally soil applied early in the season, foliar application is recommended later in the season, because imidacloprid is slowly taken up by the roots and translocated throughout the plant. By the time imidacloprid builds up to high enough levels in the leaves, aphids are already present and have damaged leaves.

Foliar application may also help to slow the development of resistance, because aphids are not subjected to sublethal doses of imidacloprid, which may be the case with soil application. Researchers have some evidence of resistance to imidacloprid in California, Texas and New Mexico. Furthermore, growers have observed what appears to be imidacloprid resistance in Arizona.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

UPDATED: 12/15
Calculate impact of pesticide on air quality
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. Not all registered pesticides are listed. Always read the label of the 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.
 
A. IMIDACLOPRID
  (various) Label rates 12 See label
  MODE-OF-ACTION GROUP NUMBER1: 4A
  COMMENTS: Soil-applied formulations of imidacloprid must be applied preventively before monitoring indicates a need; use if aphids have been a chronic problem in past years. Use foliar applications later in the season, which may help to slow the development of resistance because aphids are not subjected to sublethal doses (as may be the case with soil applications). Do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
B. SPIROTETRAMAT
  (Movento) 6–9 fl oz 24 7
  MODE-OF-ACTION GROUP NUMBER1: 23
  COMMENTS: Do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
C. PYMETROZINE
  (Fulfill) 4 oz 12 14
  MODE-OF-ACTION GROUP NUMBER1: 9B
  COMMENTS: A selective feeding blocker. Low toxicity to beneficial insects, but do not apply when bees are actively foraging.
 
D. DIMETHOATE
  (Dimethoate E267) 1 pt 48 21
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: Ground application only. Do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
E. POTASSIUM SALTS OF FATTY ACIDS#
  (DES-X, M-Pede) Label rates 12 0
  MODE-OF-ACTION GROUP NUMBER1: unknown
  COMMENTS:
 
F. AZADIRACHTIN#
  (Neemazad 1EC, Neemix 4.5) Label rates 4 0
  MODE-OF-ACTION GROUP NUMBER1: un
  COMMENTS: For larval stages.
 
G. NARROW RANGE OIL# Label rates See label 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.
 
H. CHLORPYRIFOS + GAMMA-CYHALOTHRIN*
  (Cobalt) 26-57 fl oz 24 28
  MODE-OF-ACTION GROUP NUMBER1: 1B + 3A
  COMMENTS: Highly toxic to bees. Do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
I. CHLORPYRIFOS*
  (Lorsban Advanced) 1–4 pt 24 28
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS: Use chlorpyrifos in combination with one of the other insecticides listed in this table. Avoid runoff and drift into surface waters. Certain formulations emit high amounts of volatile organic compounds (VOCs); use low-VOC formulations.
 
Restricted entry interval (REI) is the number of hours from treatment until the treated area can be safely entered without protective clothing. Preharvest entry interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI 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 (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their website at http://www.irac-online.org/.
# Acceptable for use on organically grown produce. Check with your certifier if use is permissible.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Pecan
UC ANR Publication 3456

Insects

R. Heerema, Extension Plant Sciences, New Mexico State University
C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter and 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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