How to Manage Pests

UC Pest Management Guidelines

Almond

Navel Orangeworm

Scientific name: Amyelois transitella

(Reviewed 3/09, updated 11/12, corrected 6/13)

In this Guideline

DESCRIPTION OF THE PEST

Navel orangeworm is a primary pest of almonds in California and is found on several hosts. Adult moths have irregular, silver gray and black forewings and legs and a snoutlike projection at the front of the head. Females begin egg laying about 2 nights after emergence. Eggs are laid on mummy nuts in the trees or on new crop nuts after the initiation of hullsplit, and hatch within 4 to 23 days, depending on temperature. Eggs are white in color when first laid, later turning orange in color just before hatching. Newly hatched larvae are reddish orange and later vary from milky white to pink in color. Larvae have reddish brown head capsules and a pair of crescent-shaped marks on the second segment behind the head. Pupae are light to dark brown, encased in a woven cocoon, and found inside nuts or between hulls and shells. There are three to four adult flight periods per year. The larvae overwinter in mummy nuts either in trees or on the ground.

DAMAGE

First-instar larvae bore into the nutmeat, and later instars can consume most of the nut, producing large amounts of webbing and frass. Usually more than one larva can be found feeding in a nut. Navel orangeworm larval damage can also lead to fungal infections. Some cultivars are more susceptible to damage, especially later-maturing softshell almonds with a lengthy hullsplit period or a poor shell seal.

MANAGEMENT

Two cultural practices—effective removal and destruction of mummy nuts in fall or winter and rapid, early harvest—provide the most effective control of navel orangeworm. Insecticide treatments are needed when these practices are not carried out properly, when infested alternate host trees (fig, pomegranate, or pistachio) are nearby, or to achieve very low levels of damage. When infested trees of these alternate hosts are harvested, navel orangeworm moths may migrate into almond orchards. Treating border rows (at least 10 rows) may be adequate to prevent the moths from infesting the almond crop when navel orangeworm densities are low to moderate in a given area. Sprays are timed using egg traps, monitoring of hullsplit, and/or degree-days. Two parasitic wasps may be found in orchards, but they cannot be relied on to provide effective control alone without other cultural or compatible chemical practices also being used.

Unless the orchard is close to overwintering sites, navel orangeworm pressure tends to become increasingly greater as one moves further south in the San Joaquin Valley.

Biological Control

Parasitic wasps that are known to parasitize navel orangeworm include Copidosoma (=Pentalitomastix) plethorica and Goniozus legneri. Goniozus legneri is now available from commercial insectaries and can be purchased and released. Releases must be supplemented with cultural and other management practices for good control of navel orangeworm.

Cultural Control
Removal of mummy nuts

Remove mummy nuts from trees before bud swell by mechanically shaking the tree or by hand poling. Trees should be cleaned to less than two mummies per tree by February 1 in the Sacramento Valley, and fewer in the San Joaquin Valley where winter storms or bird and squirrel activity are not adequate for natural removal of the mummies. Blow or sweep fallen mummy nuts to the row center and destroy them by discing or flail mowing by March 15 where ground cover is not present. Moist orchard floor conditions provided by winter-resident vegetation and rain will enhance mortality of navel orangeworms in mummy nuts that have fallen from trees.

Sample for mummy nuts

Sample your orchard for mummy nuts on or before January 15 to determine if further shaking is required. Examine and count the overwintering nuts on 20 trees per block to determine the average number of mummies. Refer to the previous section for guidelines for their removal and destruction.

Early harvest

Harvest nuts as soon as good removal can be achieved; this is when 100% of nuts are at hullsplit at the 6- to 8-foot level of tree canopy. If susceptible nuts can be harvested (i.e. removed from the tree) before third-generation eggs are laid, sprays will not be needed. Keep track of navel orangeworm development by using egg traps and degree-day calculations.

Organically Acceptable Methods

Cultural and biological controls and sprays of Entrust formulation of spinosad or Bacillus thuringiensis are organically acceptable methods. Sprays are not a substitute for cultural practices, which are necessary for acceptable control.

Monitoring and Treatment Decisions

In orchards where a thorough sanitation program and early harvest are carried out, insecticide applications are not usually needed unless there is a source of moths from infested trees outside the orchard. If cultural controls are not properly implemented, an insecticide application may be necessary. A harvest sample will help to evaluate the effectiveness of your management program.

Treatment is generally required in orchards that have more than two mummies (fewer in the central and southern San Joaquin Valley) remaining per tree after bud swell. Usually only one treatment is necessary to keep kernel damage below 2% at harvest and when nuts are removed before the start of the third flight. Depending on the product used, applications can be made either in spring or at hullsplit. Dormant sprays do not control navel orangeworm. If you also need to control peach twig borer and leafrollers, because a dormant or bloom spray was not applied, you may be able to apply one spray in spring (May) for all three insects, if degree-day calculations indicate that egg hatch for peach twig borer, leafrollers, and navel orangeworm will occur within a few days of each other. Only apply pyrethroids during hullsplit, because they can cause mite numbers to increase and will have a long-term negative impact on pollinators and natural enemies. In general, pyrethroids are more appropriate for protecting late almond varieties.

Spring sprays

Apply a spring spray for navel orangeworm just after the first eggs of the spring brood hatch using reduced-risk products, the insect growth regulator methoxyfenozide, diamide chlorantraniliprole or flubedimide, or spinosyns such as spinosad and spinetoram. Spinetoram and spinosad are toxic to bees, so only apply when bees are not foraging. Apply at night to avoid bee activity and because spinetoram works best when moths are active, which occurs at night. Under moderate pest pressure Bt could be used as well.

The time of brood hatch will vary according to year and location, so use degree-day accumulations to predict egg hatch (lower threshold of 55°F; upper threshold of 94°F).

The biofix for the start of degree-day accumulation is the beginning of a consistent increase in egg laying on egg traps. When at least 50% of the egg traps in a given location show increases in the number of eggs on two consecutive monitoring dates, the biofix point is the first of those two dates. (Be sure to remove eggs from the trap after it is examined.) Egg hatch is expected when 100 DD have accumulated.

Navel orangeworm egg traps

Back up degree-day accumulations with observations of eggs deposited on traps to determine when egg hatch begins. Black egg traps baited with almond presscake and 3–10% almond oil are more effective than white egg traps with presscake alone. Fill traps half- to three-quarters-full. Keep presscake dry; if it gets wet, lumpy or moldy, replace it. Remember that egg-trap counts will not tell you if a spray is needed, only that moths are present and are laying eggs. Egg traps will have few eggs following hullsplit, once new crop nuts have cracked, but eggs will again be laid on the traps following harvest. Evaluate your orchard considering the criteria mentioned above to determine if you need to spray. More details on monitoring procedures and a form for keeping track of egg-trap counts are included in the online version of this guideline.

Hullsplit sprays

If you choose to treat at hullsplit, time the spray to the beginning of hullsplit if eggs are being laid on egg traps; otherwise time it to an increase in egg-laying on traps or the predicted initiation of egg-laying following hullsplit. Hullsplit is determined to begin when sound fruit in the tops of the trees begin to split. At this time, the nuts at eye level will be less mature than those at the top and have only a deep furrow in the hulls. Nuts in the top southwest quadrant of the tree split first. Blank nuts (usually 3 to 5%) will split 1 to 2 weeks ahead of sound nuts. Use a long-extension pole pruner to cut small branches from this top portion of five or six trees in the orchard to check whether hullsplit nuts are blank or sound.

Check for eggs on egg traps. If hullsplit has begun, but eggs are not being laid, wait until egg-laying starts. After hullsplit begins, egg-laying on traps may decrease due to competition of the traps with the new crop nuts. Therefore, if you do not see eggs on traps, use degree-days and apply a treatment at 1200 degree-days from spring biofix.

Postharvest fumigation

If the crop was exposed to a significant third flight of navel orangeworm or peach twig borer before harvest, a postharvest fumigation may be warranted.

Common name Amount per acre** R.E.I.‡ P.H.I.‡
(trade name) (conc.) (dilute)
(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 and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
SPRING SPRAYS
 
A. METHOXYFENOZIDE
  (Intrepid 2F) Label rates 4 14
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: An insect growth regulator.
 
B. SPINETORAM
  (Delegate WG) 6–7 oz 1.5–1.75 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Apply at night to target active adult moths and to avoid foraging bees.
 
C. SPINOSAD
  (Entrust)# 1.25–3 oz 0.3–0.75 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Apply in early morning or evening when bees are not actively foraging. Does not appear to be disruptive of natural enemies except predaceous thrips and some parasitoids.
 
D. CHLORANTRANILIPROLE (RYNAXYPYR)
  (Altacor) 3.0-4.5 oz 4 10
  MODE OF ACTION GROUP NUMBER1: 28
 
E. EMAMECTIN BENZOATE
  (Proclaim) 3.2-4.8 oz 0.8-1.2 oz See label 14
  MODE OF ACTION GROUP NUMBER1: 6
 
F. FLUBENDIAMIDE
  (Belt) 3.0-4.0 oz 12 14
  MODE OF ACTION GROUP NUMBER1: 28
 
G. FLUBENDIAMIDE/BUPROFEZIN
  (Tourismo) 10-14 fl oz 12 60
  MODE OF ACTION GROUP NUMBER1: 16, 28
  COMMENTS: Similar efficacy as Belt, but also contains buprofezin, an insect growth regulator that kills scales and some other Hemipterans and beetles. When using this material, consider potential effects on beneficial insects.
 
H. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: Effective only under moderate pest pressure. Make 2 applications, one at the beginning of egg hatch (100 degree-days) and the second 10 to 14 days later. Check with certifier to determine which products are organically acceptable.
 
HULLSPLIT AND POST-HULLSPLIT SPRAYS
 
A. METHOXYFENOZIDE
  (Intrepid 2F) Label rates 4 14
  MODE OF ACTION GROUP NUMBER1: 18A
 
B. SPINETORAM
  (Delegate WG) 6–7 oz 1.5–1.75 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
 
C. CHLORANTRANILIPROLE (RYNAXYPYR)
  (Altacor) 3.0-4.5 oz 4 10
  MODE OF ACTION GROUP NUMBER1: 28
 
D. SPINOSAD
  (Entrust)# 1.25–3 oz 0.3–0.75 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Does not appear to be disruptive of natural enemies except predaceous thrips and some parasitoids.
 
E. FLUBENDIAMIDE
  (Belt) 3.0-4.0 oz 12 14
  MODE OF ACTION GROUP NUMBER1: 28
 
F. FLUBENDIAMIDE/BUPROFEZIN
  (Tourismo) 10-14 fl oz 12 60
  MODE OF ACTION GROUP NUMBER1: 16, 28
  COMMENTS: Similar efficacy as Belt, but also contains buprofezin, an insect growth regulator that kills scales and some other Hemipterans and beetles. When using this material, consider potential effects on beneficial insects.
 
G. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various)# Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: Make two applications: (1) at hullsplit (or start of egg-laying if after hullsplit) and (2) one week later. Check with certifier to determine which products are organically acceptable.
 
H. BIFENTHRIN
  (Brigade, Bifenture) 8-32 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application. Never use a pyrethroid insecticide as a May spray, and avoid use of pyrethroids in almond orchards if possible.
 
I. ESFENVALERATE*  
  (Asana XL) 16 oz 12 21
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application. Never use a pyrethroid insecticide as a May spray, and avoid use of pyrethroids in almond orchards if possible.
 
J. LAMBDACYHALOTHRIN
  (Warrior with Zeon) 2.56-5.12 fl oz 24 14
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application. Never use a pyrethroid insecticide as a May spray, and avoid use of pyrethroids in almond orchards if possible.
 
K. CHLORANTRANILIPROLE/LAMBDACYHALOTHRIN
  (Voliam Xpress) 6.0-12.5 fl oz 24 14
  MODE OF ACTION GROUP NUMBER1: 28, 3
  COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application. Never use a pyrethroid insecticide as a May spray, and avoid use of pyrethroids in almond orchards if possible.
 
L. FENPROPATHRIN*
  (Danitol) 10-2/3 – 21-1/3 fl oz 24 3
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application. Never use a pyrethroid insecticide as a May spray, and avoid use of pyrethroids in almond orchards if possible.
 
M. CHLORPYRIFOS*
  (Lorsban 4E) 2 qt 24 14
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Do not apply more than 3 foliar applications per season. Do not allow livestock to graze in treated orchards. Avoid drift or tailwater runoff into surface waters.
 
N. PHOSMET
  (Imidan 70WP) 4 lb 1 lb 72 30
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Do not apply more than twice per season as a foliar spray. This material is a good choice near residential areas. Breaks down rapidly in water. Can be used where label restrictions prevent use of other organophosphates. Late-season treatments must be applied before hullsplit reaches 10%.
 
MATING DISRUPTANTS
 
A. MATING DISRUPTANTS
  (Puffer NOW) Label rates 0 0
 
POSTHARVEST
 
A. ALUMINUM PHOSPHIDE* Label rates See label 0
  MODE OF ACTION: Unknown. An inorganic insecticide.
  COMMENTS: Apply as fumigant to harvested almonds that have been exposed to navel orangeworm.
 
** For dilute applications, rate is per 100 gal water to be applied in 300–500 gal water/acre, depending on the label; for concentrate applications, use 80–100 gal water/acre, or lower if the label allows.
* Permit required from county agricultural commissioner for purchase or use.
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 these two intervals is the minimum time that must elapse before harvest may occur.
# Acceptable for use on organically grown produce.
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/.
Not recommended or not on label.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Almond
UC ANR Publication 3431

Insects and Mites
    • F. G. Zalom, Entomology, UC Davis
    • C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter/Yuba counties
    • W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
    • D. R. Haviland, UC IPM Program, UC Cooperative Extension, Kern County
    • R. A. Van Steenwyk, Insect Biology, UC Berkeley
    Acknowledgment for contributions to Insects and Mites:
    • R. E. Rice, Kearney Agricultural Center, Parlier
    • L. C. Hendricks, UC Cooperative Extension, Merced County
    • R. L. Coviello, UC Cooperative Extension, Fresno County
    • M. W. Freeman, UC Cooperative Extension, Fresno County

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