Provisional Guidelines For Brown Marmorated Stink Bug Control In Almond

Scientific name: Halomorpha halys

DESCRIPTION OF THE PEST

Brown marmorated stink bug, Halyomorpha halys (Family: Pentatomidae) is an invasive pest that was accidentally introduced into the Eastern United States in the late 1990s. Although it has been trapped in the Los Angeles area and elsewhere in California since the mid-2000s, the first large, established population of this pest in California was reported in 2013 in Sacramento County. It has become a nuisance pest there during late fall and winter months when large adult aggregations have been known to enter houses and apartments to overwinter. During spring and summer, this insect infests backyard trees and community gardens. As of spring 2020, there are a more than 16 counties with established populations in residential areas. In 2017, a brown marmorated stink bug infestation was first reported from a commercial almond orchard near Modesto in Stanislaus County. Since then, this stink bug has been detected alive and collected from monitoring traps in several commercial almond and peach orchards in the northern San Joaquin Valley area.

Brown marmorated stink bug adults are approximately 3/4-inch long and with shades of brown “marmorated” (marbled) coloration on the upper body surface. They are typical shield-shaped stink bugs, almost as wide as they are long. Adults and nymphs, except the 1st instar nymph, have a two white bands on their antennae and legs as clear identifying characteristics. Other related stink bug species commonly found in California (e.g., consperse stink bug, brown stink bug, rough stink bug, spined soldier bug) and the leaffooted bug (Family Coreidae) lack these key features. To distinguish brown marmorated stink bug (BMSB) from other similar-looking insects that you might find in an almond orchard, see Table 1 below.

Table 1. Identification of Large Bugs Found in Almond Orchards
CHARACTERISTIC Brown marmorated stink bug Consperse stink bug Redshouldered stink bug Rough stink bug Leaffooted bug
Antennae Two white bands on antennae No white bands on antennae No white bands on antennae No white bands on antennae No white bands on antennae
Legs Marbled brown with faint white band Distinct dark spots on legs Green with red feet Gray Leaf-like structure on the hind legs
Body Shield-shaped mottled brown Shield-shaped grayish brown to green Shield-shaped green Shield-shaped speckled white and gray Not shield-shaped; narrow brown body
Shoulders Smooth shoulder edge Smooth shoulder edge Pink or red line across the shoulder Spines along its shoulder edge that feels serrated or ‘rough’
Head Single notch below each eye. No “tooth” on each side of face. No “tooth” on each side of face. No notch below eye. No “tooth” on each side of face. No notch below eye. “Tooth”on each side of its face. No notch below each eye. No “tooth” on each side of face. No notch below eye.
Size 3/4 inch long 1/2 inch long 1/2 inch long 3/4 inch long 1 inch long

Brown marmorated stink bug is a polyphagous insect that feeds on over 170 host plants in the United States, including ornamental and landscape tree species. Some major host crops include apples, peaches, nectarines, pears, cherries, grapes, peppers, tomatoes, sweet corn, beans, and soybean. This stink bug has become an economically-important pest of hazelnuts in Oregon. Adults commonly overwinter in human-made structures such as houses, barns, shops, and even in dry and dead trees during the fall and early winter.

In spring, within two-weeks after emergence, overwintering adults mate and are ready to deposit eggs in host plants. Females lay a cluster of around 28 eggs on the underside of leaves. Eggs are light green when first laid and gradually become whitish near and after hatching. A single female can produce over 480 eggs in a lifetime.

It takes approximately 964 degree-days (DD) (base = 57.2oF) for eggs to develop into adults, and adults of the first generation live about 45 days. Brown marmorated stink bug has two overlapping generations per year. There are five nymphal or immature life stages known as instars. First instars have dark, reddish eyes and a yellow-reddish body with a black stripe. They do not feed and are typically clustered around the egg mass after hatching. Second through fifth instar nymphs are dark black to brown and actively walk searching for food; only the adult stage can fly.

DAMAGE

Brown marmorated stink bug has caused severe crop loss in commercial tree fruits and vegetable crops throughout the United States. It has caused damage to almonds and peaches in California since 2017, with economically significant damage being reported in a few almond orchards in the San Joaquin Valley area.

Early season feeding (March–May) by brown marmorated stink bug can cause substantial injury to developing nuts, including aborted and dropped nuts. Late-season feeding (June-July), in contrast, can cause shriveled and ‘dimpled’ kernels at harvest. Gumming can occur with early- or late-season brown marmorated stink bug infestations. Repeated feeding on developing almonds leads to gummy nuts with multiple puncture spots. Damaged nuts show feeding signs both externally (multiple gumming sites, light brown speckles, and yellowing) as well as internally (pinholes, water-soaked lesions, corky tissue, and internal gumming. See Table 2 below for a summary of brown marmorated stink bug damage compared to other large bugs found in California almond orchards.

Table 2. Summary of Large Bug Feeding Damage Symptoms in Almond Orchards
Description Native Stink Bugs Leaffooted Bug (LFB) Brown Marmorated Stink Bug (BMSB)
Generation(s) causing damage Overwintering adults Overwintering adults Overwintering adults and in-season adults and nymphs
Gummosis (clear gumming) Multiple gumming spots per nut: thread-like gumming 1-2 feeding spots per nut: thread-like gumming Multiple gumming spots per nut: ‘glob-like’ gumming
Nut drop Not common Common
(March-April)
Common
(March-early May)
Kernel damage Wrinkled or dark spots. Late-season feeding may not damage kernel. Aborted or gummy or sunken dark spots. Aborted or gummy or sunken dark spots.

Although adults cause more severe damage than nymphs, both nymphs and adults feed on almond. They feed by inserting their piercing-sucking, needle-like mouthparts into the fruit and other vegetative tissue. A digestive enzyme is injected through their mouthparts upon feeding to liquefy the plant tissue for easy uptake of nutrients. On the fruit, feeding results in a characteristic necrotic lesion on the hull.

Some of these feeding damage symptoms match those produced by leaffooted bug and native stink bug feeding on almond. However the timing and duration of damage varies among these pests (see Table 3).

  • Leaffooted bug feeding is significant from late March through May.
  • Native stink bugs are problematic during June to July.
  • Brown marmorated stink bug can attack almond fruit throughout the growing season beginning in mid-March and lasting through July.

Compared to these other insect pests, brown marmorated stink bug is a significant threat to almond production for a greater portion of the growing season and numbers of bugs found infesting almond orchards tend to be much higher.

Table 3. Summary of Timing of Large Bug Feeding, Damage, and Prevalence in Almond Orchards
Description Native Stink Bugs Leaffooted Bug (LFB) Brown Marmorated Stink Bug (BMSB)
Generation(s) causing damage Overwintering adults Overwintering adults Overwintering adults and in-season adults and nymphs
Damage timing June–July Late March–May March–July
Mid-to-late season feeding occurrence Yes (June–July) Not significant Yes (May–July). Capable of penetrating into the kernel

Based on field observations, some varieties such as Fritz, Monterey, Aldrich, Butte are more susceptible than Nonpareil. The presence of adults and the damage have been noticeably higher in border rows, especially near sides of the orchard next to an open field or by alternate hosts such as tree of heaven, Ailanthus altissima. Tree of heaven plants tend to be more abundant in or around residential areas, including neighboring orchards.

MANAGEMENT

Brown marmorated stink bug requires management at the landscape-level since it invades orchards from nearby woodlots, residential host plants, and overwintering structures. Therefore, orchard edges are at the greatest risk for crop damage. Monitoring brown marmorated stink bug using pheromone-baited traps and visual searches is important. If this insect is detected on almond acreage early season, targeted pest management can begin as early as March and continue through June or July in some late almond varieties.

Biological Control

Several generalist arthropod predators may provide biological control services by attacking this pest and its eggs. A common egg predator in California urban settings is the Trachelas sp. spider. However, it only damages a few eggs with each visit. Other predators include assassin bugs, ground beetles, lady beetles, jumping spiders, praying mantis, earwigs, ground beetles, damsel bugs, and certain species of crickets and katydids. Although these predators were reported to attack native stink bugs as well as brown marmorated stink bug in various parts in the U.S., their impact in reducing exotic brown marmorated stink bug densities is minimal.

Several species of tiny, native wasps parasitize the eggs of native stink bugs. However, the level of egg parasitization of brown marmorated stink bug by these species is very low, so they do not significantly reduce this pest’s abundance at present. Therefore, these native parasitoids may not provide adequate control to minimize the economic loss in commercial almond orchards.

In 2018, a brown marmorated stink bug-specific egg parasitoid from Asia, Trissolcus japonicus, was detected in Los Angeles County. Surveys from China, part of this parasitoid’s native home range, indicate it can provide effective biological control for this pest. Lab and field studies in North America show promise for targeted biological control because this parasitoid has a limited ecological host range with a strong preference for brown marmorated stink bug eggs. However, this parasitoid’s actual impact on this stink bug in orchard systems throughout California has yet to be evaluated.

Cultural Control

Pay close attention to potential overwintering sites and alternate hosts such as tree of heaven if present nearby and eliminate them if possible. They support brown marmorated stink bug populations throughout the season and can serve as a source of orchard infestations.

Organically Acceptable Methods

Biological and cultural controls can be used in an organic production system. Trials with products approved for use in organic production have been conducted in other states in various crops with varying degrees of success. These include azadirachtin plus pyrethrins (Azera), azadirachtin plus pyrethrins plus potassium salts of fatty acid (Azera+M-Pede), azadirachtin (Aza-Direct), spinosad (Entrust), pyrethrin (Pyganic), and pyrethrin plus kaolin clay (Pyganic+Surround). No efficacy information exists for these products in California almonds. Check with your organic certifier and read label instructions before using any pesticides.

Monitoring and Treatment Decisions

A trap baited with a brown marmorated stink bug aggregation pheromone and pheromone synergist, methyl decatrienoate, is effective in monitoring adults and nymphs season-long, even when low numbers are present. Use sticky panel traps (9x12-inch double-sided sticky) that can be affixed near the top of a wooden stake at about 4 feet above ground level. The lures should be suspended on top near to the sticky panel. Use a minimum of three sticky panel traps per orchard. The traps should be placed in a border-tree row adjacent to open fields, houses, or any other potential overwintering site from which the adult bugs may migrate into the orchard.

Trap captures may not be representative of the brown marmorated stink bug density in the orchard since the performance of lures can vary with the crop monitored. In almond orchards, the trap counts often underrepresents the orchard population and damage; adults and feeding activities in the tree have been seen in orchards without trap captures. Therefore, it is important to regularly scout for this pest and its damage in the orchard if it is believed to occur in the area. Visual observations of the insect (egg mass, nymphs, adults) and damaged fruits (deformed or exuded nuts) and beat tray sampling (shaking branches/twigs to dislodge insects) are early detection methods. Visual observations of the border trees for the presence of insects and fruit gumming are highly recommended.

No treatment threshold has been developed for this pest in almonds. At this time, the presence of any brown marmorated stink bugs in traps together with a confirmation by visual surveys should be of concern since almond nuts are highly susceptible to abortion and drop. Consider a spring spray for control. However, proper identification is critical before making management decisions, as there are many other insects that can be mistaken for brown marmorated stink bug. One look-alike, the rough stink bug, does not feed on almonds and is a beneficial predator that assists with biological control in almond orchards. Use Table 1 above to distinguish brown marmorated stink bug from other similar insects before applying any insecticides for this pest.

Chemical Control

Because brown marmorated stink bug is a newly established pest in California, a management program for California crops is still being developed. Consult your local UC cooperative extension advisor or agricultural commissioner for more information on management plans for brown marmorated stink bug in your area.

Pyrethroid insecticides are considered effective against this pest. However, pyrethroids have short residual control. They are also a poor fit in an integrated pest management (IPM) program, especially early season, because of their negative impact on natural enemies. For example, the use of pyrethroids in the spring can flare up mite population in almonds.

If multiple sprays are needed, consider border sprays for follow-up applications because of the brown marmorated stink bug’s tendency to be found near orchard borders nearest potential overwintering hosts. If frequent sprays are needed, consider alternate-row-middle applications, which are used in other tree crops such as apple and peach in other states. Rotate insecticides among products with different modes of action classes and group numbers.

Always read, understand, and follow the label directions before using any pesticide. Below are some insecticide options based on lab assays using detached almond fruit as a substrate, and on studies conducted on orchard crops in other states.

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

Not all registered pesticides are listed. 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. Always read the label of the product being used.
 
BROAD-SPECTRUM FOLIAR SPRAYS
A. BIFENTHRIN
(Brigade WSB) 32 oz 12 7
MODE-OF-ACTION GROUP NUMBER1: 3A
COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application; will cause secondary pest outbreaks, especially spider mites, if used before hullsplit. Avoid use of pyrethroids in almond orchards if possible.
 
B. LAMBDA-CYHALOTHRIN
(Warrior II with Zeon) 2.56 fl oz 24 14
MODE-OF-ACTION GROUP NUMBER1: 3A
COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application; will cause secondary pest outbreaks, especially spider mites, if used before hullsplit. Avoid use of pyrethroids in almond orchards if possible.
 
C. LAMBDA-CYHALOTHRIN/CHLORANTRANILIPROLE
(Besiege) 12.5 fl oz 24 14
MODE-OF-ACTION GROUP NUMBER1: 3A/28
COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application; will cause secondary pest outbreaks, especially spider mites, if used before hullsplit. Avoid use of pyrethroids in almond orchards if possible.
 
D. PERMETHRIN
(Perm-Up 3.2EC) 10 fl oz 12 7
MODE-OF-ACTION GROUP NUMBER1: 3A
COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application; will cause secondary pest outbreaks, especially spider mites, if used before hullsplit. Avoid use of pyrethroids in almond orchards if possible.
 
E. FENPROPATHRIN
(Danitol 2.4EC) 21.33 fl oz 24 3
MODE-OF-ACTION GROUP NUMBER1: 3A
COMMENTS: Pyrethroid residues are very toxic to beneficial predators and parasitoids long after application; will cause secondary pest outbreaks, especially spider mites, if used before hullsplit. Avoid use of pyrethroids in almond orchards if possible. For resistance management, make no more than two applications of Danitol per season.
 
F. CLOTHIANIDIN
(Belay) 6 fl oz 12 21
MODE-OF-ACTION GROUP NUMBER1: 4A
COMMENTS: Provides partial control of adult bugs on contact but does not have any residual control once residues have dried. Most effective when used in a tank mix with bifenthrin or lambda cyhalothrin. Applications restricted to post bloom through initiation of harvest.
 
G. ACETAMIPRID
(Assail 70 WP) 4.1 oz 12 14
MODE-OF-ACTION GROUP NUMBER1: 4A
 
ORGANIC
Note: Many organic products have low residual efficacy and therefore may require more frequent pesticide applications.
 
A. AZADIRACTIN/PYRETHRINS
(Azera Insecticide)# 3.5 pt 12 0
MODE-OF-ACTION GROUP NUMBER1: un/3A
COMMENTS: Multiple modes of action: repellent, antifeedant, and insect growth regulator. Low to moderate toxicity to beneficial insects.
 
B. AZADIRACTIN/PYRETHRINS
(Azera Insecticide)# 3.5 pt 12 0
MODE-OF-ACTION GROUP NUMBER1: un/3A
...PLUS...
POTASSIUM SALTS OF FATTY ACID
(M-Pede)# 1–2% v/v solution 12 0
MODE OF ACTION:
COMMENTS: Multiple modes of action: repellent, antifeedant, and insect growth regulator. Low to moderate toxicity to beneficial insects.
 
C. AZADIRACTIN
(Aza-Direct)# 3.5 pt 4 0
MODE-OF-ACTION GROUP NUMBER1: un
COMMENTS: Multiple modes of action: repellent, antifeedant, and insect growth regulator. Low to moderate toxicity to beneficial insects.
 
D. SPINOSAD
(Entrust SC)# 10 fl oz 4 1
MODE-OF-ACTION GROUP NUMBER1: 5
COMMENTS: May be disruptive of predaceous thrips and some parasitoids.
 
E. PYRETHRINS
(Pyganic EC5.0)# 15.61 fl oz 12 0
MODE-OF-ACTION GROUP NUMBER1: 3A
COMMENTS: Pyrethrins rapidly break down after application. They must be applied when target pests are present. May be disruptive to beneficial insects.
 
F. PYRETHRINS
(Azera Insecticide)# 3.5 pt 12 0
MODE-OF-ACTION GROUP NUMBER1: 3A
...PLUS...
KAOLIN CLAY
(Surround WP)# 75 lb 4 0
MODE OF ACTION: un
COMMENTS: Pyrethrins rapidly break down after application. They must be applied when target pests are present. May be disruptive to beneficial insects.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest 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 may occur.
1 Rotate pesticides 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; pesticides with a 1B group number should be alternated with pesticides 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).
# Acceptable for use on organically grown produce.

AUTHORS

J.R. Rijal UC IPM and UC Cooperative Extension Stanislaus County
F.G. Zalom (emeritus), Entomology, UC Davis

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