How to Manage Pests

UC Pest Management Guidelines

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 new crop nuts and hatch within 4 to 23 days, depending on temperature. Eggs are not laid on new crop nuts until initiation of hull split. 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 hull split period or a poor shell seal.

MANAGEMENT

Two cultural practices-effective removal of mummy nuts in fall or winter and rapid, early harvest-provide the most effective control of navel orangeworm. Insecticide treatments are needed only when these practices are not carried out properly, or where infested trees, such as fig or pomegranate, are nearby. If infested crops 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. Sprays are timed using egg traps, monitoring of hull split and/or degree-days. Two introduced parasitic wasps may be found in orchards, but they cannot be relied on to provide effective control alone.

Biological Control

Several parasitic wasps are known to parasitize navel orangeworm, including 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 budswell by mechanically shaking the tree or by hand poling. Trees should be cleaned to less than two mummies per tree by February 1. Blow or sweep fallen mummy nuts to the row center and destroy them by disking or flail moving by March 15. Moist orchard floor conditions provided by winter cover crops will enhance mortality of navel orangeworms that are 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 20 trees per block. Use a long extension pole pruner to collect nuts. If an average of 2 or more mummies are found, remove mummies throughout the orchard by February 1 and destroy them by flail mowing before March 15.

Early harvest. Harvest nuts as soon as good removal can be achieved; this is when 95% of nuts are at hull split at the 6 to 8 foot level of tree canopy. If nuts can be harvested and removed from the orchard 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 Entrust (spinosad) sprays at hull split are organically acceptable methods. Sprays are not a substitute for cultural practices, which are necessary for acceptable control.

Monitoring and Treatment     Degree-day calculator    Degree-day table

In orchards where a 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 remaining per tree after budswell. Usually only one treatment is necessary and can be applied either in spring or at hull split. If you also need to control peach twig borer because a dormant or bloom spray was not applied and peach twig borer is a concern in the orchard, you may be able to apply your spray in spring to control both peach twig borer and navel orangeworm if degree-day calculations indicate that egg hatch for both species will occur within a few days of each other.

Spring sprays. Apply a spring spray for navel orangeworm just after the first eggs of the spring brood hatch using spinosad or the insect growth regulators methoxyfenozide (Intrepid) or tebufenozide (Confirm). The time of brood hatch will vary according to year and location, so use degree-day accumulations to predict egg laying (lower threshold of 55°F; upper threshold of 94°F). For assistance in calculating degree-days, see "degree-days" on the UC IPM Web site.

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.

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. 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. Evaluate your orchard using the criteria listed above to determine if you need to spray. See more details on monitoring procedures and a form (PDF* 50K) for keeping track of egg trap counts.

Hull split sprays. If you choose to treat at hull split, time the spray to the beginning of hull split if eggs are being laid on egg traps; otherwise time it to the initiation of egg laying following hull split. Hull split 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. Use a long-extension pole pruner to cut small branches from this top portion of five or six trees in the orchard to check for initiation of hull split.

Check for eggs on egg traps. If hull split has begun but eggs are not being laid, wait until egg laying starts. However, after hull split begins, egg laying on traps may decrease. If you are not seeing eggs on traps, use degree-day information 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.

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PUBLICATION

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
R. L. Coviello, UC Cooperative Extension, Fresno Co
R. A. Van Steenwyk, Insect Biology, UC Berkeley
M. W. Freeman, UC Cooperative Extension, Fresno Co.
Acknowledgment for contributions to the insects and mites section:
R. E. Rice, Kearney Agricultural Center, Parlier
L. C. Hendricks, UC Cooperative Extension, Merced Co.

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