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How to Manage Pests
UC Pest Management Guidelines
Walnut
Navel Orangeworm
Scientific Name: Amyelois transitella
(Reviewed 12/07,
updated 12/07)
In this Guideline:
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Navel orangeworm overwinters as larvae inside mummy nuts on the tree
and in trash nuts left on the ground and around hullers. Pupation begins in
March and may continue through early May. Moths of the overwintered brood start
emerging in April, and peak emergence usually occurs from late April to
mid-May, depending on season and locality.
The adult moth is silver gray with irregular black patches on the forewings. The snoutlike
palps in front of the head help distinguish this moth from the codling moth.
Females of the overwintered generation lay their eggs singly on mummy nuts,
codling moth-infested nuts, or blighted nuts. The first generation, and most of
the second, is completed in these nuts. In late summer, some of the second
generation larvae infest the new crop as the husks begin to split. Females
emerging at this time prefer to lay eggs on the opened husk or on the exposed
nutshell.
Eggs of
the navel orangeworm are opaque white when first laid. After about a day, they turn pink,
then reddish orange. The navel orangeworm larva has a pair of brown, crescent-shaped marks on the second segment behind the head. These marks are absent on codling
moth larvae. After hatching, the tiny caterpillars enter nuts through the soft
tissue at the stem end and do not emerge until they are adults. Several larvae
may infest one nut and produce substantial webbing. In
contrast, only a single codling moth is found in each nut, and the codling moth
produces little webbing.
Nuts infested with navel orangeworm are unmarketable because the larvae
feed on the nutmeats and produce webbing and frass. Navel orangeworm do not
damage sound walnuts until the husks begin to split. Nuts infested only by the
navel orangeworm may show no external signs of webbing or frass, but shells of
heavily infested nuts will have an oily appearance.
Management of navel orangeworm relies on using good orchard
sanitation to eliminate overwintering and feeding sites and on harvesting the new
crop before the worms can enter the nuts. Good control of codling moth, walnut
blight, and sunburn is also essential because navel orangeworm attacks only
walnuts with damaged or split husks. Insecticides currently registered for the
control of navel orangeworm in walnuts are not very effective, so preventing
infestations is the most reliable approach. Harvest as soon as nuts are ready;
do not allow them to remain on the tree into the fourth generation.
Biological Control
Two wasps that parasitize the navel orangeworm, Copidosoma
(=Pentalitomastix) plethorica and Goniozus
legneri, are established in many
walnut and almond growing areas and account for some larval mortality. A ground
cover maintained during winter aids in decomposing trash nuts by molds and
other microorganisms.
Cultural Control
A good sanitation program is essential for navel orangeworm management.
There are three phases to the program:
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Reduce overwintering populations by removing remaining nuts from trees and
flailing or burning all crop waste containing nuts, before mid-March. This
includes removing all mummy nuts found in the trees during the dormant period,
all windfall and huller waste materials found in the field, and all waste
materials cleaned up from bins, hulling and drying equipment, and buildings
after harvest and dehydration.
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Reduce damaged nuts that allow entry of naval orangeworm and population
increase during the season by controlling both walnut blight and codling moth,
especially second generation.
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Harvest as early as possible. Use of ethephon to advance husk splitting is
advantageous, particularly during heavy worm populations or prolonged dry
falls. (For more information, see USING ETHEPHON).
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Dry nuts immediately and either fumigate on the farm, if stored, or ship
immediately to a facility where fumigation will be performed.
Organically Acceptable Methods
Biological and cultural control are acceptable in an organically
certified crop.
Monitoring and Treatment Decisions
Insecticide treatments should not be necessary in most orchards where a good
cultural program has been carried out; in any event, chemical treatments are
only partially effective (about 50% control) against navel orangeworm infestations.
Monitor split nuts and nuts on the ground for egg laying from the third generation. If
egg laying is occurring at husk split, harvest promptly to avoid damage.
At harvest, collect and crack out 1,000 nuts to assess
damage and to plan for next year.
| Common name |
Amount to Use** |
R.E.I.+ |
P.H.I.+ |
| (trade name) |
(conc.) |
(dilute) |
(hours) |
(days) |
|
| 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. |
| |
| THIRD FLIGHT and THIRD GENERATION
LARVAE |
| A. |
METHOXYFENOZIDE |
| |
(Intrepid) 2F |
16–24 fl oz |
— |
4 |
14 |
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MODE OF ACTION GROUP NUMBER1: 18A |
| |
COMMENTS: An insect growth regulator that
provides 10 to 18 days of residual protection depending on the rate of
application and nut expansion. Kills young larvae but does not kill adult
moths. It is a reduced risk insecticide that has little or no effect on
beneficial insects and mites. Spray coverage is extremely important. Do not
apply to large trees unless adequate spray coverage can be verified. Use no
less than 100 gal water/acre for ground applications. Sprayer speed should
not exceed 1.5 mph. The use of Latron B-1956, CS-7, or similar sticker/spreader
is highly recommended. Apply at the beginning of egg hatch, which is earlier than organophosphate or carbamate insecticide timings. |
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| B. |
PHOSMET |
| |
(Imidan) 70WP |
5 lb |
1–2 lb |
7 days |
HS |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: Do not apply more than 8.5 lb/acre/application or more than 5 times per season. Buffer to a pH of 5.5-6.0. |
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| C. |
AZINPHOSMETHYL* |
| |
(Guthion Solupak) 50% |
3 lb |
0.75 lb |
30 days |
30 |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: Do not make more than one
application/season. Use of the product on walnuts is being phased out in 2009. |
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| D. |
METHIDATHION* |
| |
(Supracide) 25WP |
4–12 lb |
2 lb |
14 days |
7 |
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MODE OF ACTION GROUP NUMBER1: 1B |
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COMMENTS: Do not graze livestock in
treated orchard. Make no more than one applications during the dormant period or more than 2 cover sprays each season. |
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| E. |
ESFENVALERATE* |
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(Asana XL) |
9.6–19.2 fl oz |
4 fl oz |
12 |
21 |
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MODE OF ACTION GROUP NUMBER1: 3 |
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COMMENTS: This is a broad-spectrum
pesticide that is harmful to beneficials at higher rates and can cause outbreaks of aphids and mites. |
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| F. |
CARBARYL* |
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(Sevin) |
Label rates |
12 |
14 |
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MODE OF ACTION GROUP NUMBER1: 1A |
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COMMENTS: Carbaryl causes mites to
reproduce more rapidly, so monitor for the mites if this material is used. This material is best used later in the season. |
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IMPORTANT LINKS
![[Precautions]](/IMAGES/btn-precautions_bul.gif)
![[UC Peer Reviewed]](/IMAGES/logo-ucpeerreviewed.jpg)
UC IPM Pest Management Guidelines: Walnut
UC ANR Publication 3471
Insects and Mites
C. Pickel, UC IPM Program/UC Cooperative Extension, Sutter/Yuba counties
W. J. Bentley, UC IPM Program/Kearney Agricultural Center, Parlier
J. A. Grant, UC Cooperative Extension, San Joaquin Co.
J. K. Hasey, UC Cooperative Extension, Sutter/Yuba counties
W. W. Coates, UC Cooperative Extension, San Benito Co.
R. A. Van Steenwyk, Insect Biology, UC Berkeley
Acknowledgment for contributions to the insects and mites section:
W. H. Olson, UC Cooperative Extension, Butte Co.
L. C. Hendricks, UC Cooperative Extension, Merced Co.
G. S. Sibbett, UC Cooperative Extension, Tulare Co.
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