Description of the Pest
The most common stink bug in almonds is the green stink bug. Adult green stink bugs are bright green with the entire lateral margin lined in yellow or orange. Green stink bug nymphs are a mixture of green, black, and orange. The redshouldered stink bug and green plant bug are smaller in size and less common. The redshouldered stink bug is somewhat triangular in shape and about 0.33 inch in length. It is predominantly green with a narrow red band across the shoulder; sometimes the band is absent. There is also a brown-colored phase, usually found in overwintering bugs. The Uhler stink bug is dull to bright green and slightly larger (0.4–0.6 inch in length).
Stink bugs often develop in weeds or field crops and migrate into almonds during spring, as weed or crop hosts dry up. The exception is the green stink bug, which overwinters within the orchard. Eggs of these stink bugs are laid in clusters, are barrel-shaped, and have concentric dark rings at the top. In almonds, they are often found on the hulls of the nuts. Immature stages resemble the adults, but are smaller, rounder, and shinier because they lack wings. They exhibit a wide range of color markings that can be different from the adult.
Do not confuse pest stink bugs with the rough stink bug, Brochymena quadripustulata, a predator that is speckled white and gray and can also be found in almonds. Nymphs of Brochymena are colored red, white, and blue.
Stink bug damage to almonds is usually caused by the green stink bug. For decades this bug never reached pest status because broad-spectrum dormant insecticide treatments prevented it from overwintering in almonds. More recently there have been increasing numbers of reports of stink bug damage, especially in the lower San Joaquin Valley, in orchards where organophosphate, carbamate, or pyrethroid insecticides have not been used for 3 to 4 years.
Damage by stink bugs usually occurs from May through July, when the bugs insert their strawlike mouthparts through the hull and into the kernel. This damage is almost identical to damage caused by leaffooted plant bugs but occurs later in the season and does not result in nut abortion. Instead, damaged nuts can be recognized by strands of ooze, called gummosis, that exude from the puncture site. Kernels of damaged nuts either become wrinkled and misshapen, or if already hardened before bug damage, will contain a black spot at the puncture site.
Monitor from May through July for gummosis on the surface of almond hulls. If found, cut a cross section through the damaged area to distinguish bug damage from physiological problems by the presence of a puncture mark on the kernel. Because stink bugs are not highly mobile, it is common to find damage in clusters, often with the bug or an egg mass still present in the vicinity.
There are currently no treatment thresholds for stink bugs. Base the decision to spray on the amount of damage and orchard history. Generally speaking, one dormant (green stink bug) or in-season broad-spectrum insecticide (all species) for any pest about every 3 years is sufficient to prevent economic damage. Where only reduced-risk products have been used and damage levels for stink bug become unacceptable, consider making an in-season spray with one of the products listed below. If stink bug numbers are high, consider applying one of these products in a tank mix with a neonicotinoid insecticide such as acetamiprid (Assail).
|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.|
|(Brigade WSB)*||8–32 oz||12||7|
|MODE-OF-ACTION GROUP NUMBER1: 3A|
|COMMENTS: Do not repeat an application in less than 15 days. Will cause secondary pest outbreaks, especially spider mites, if used before hullsplit.|
|(Warrior II with Zeon)*||1.28–2.56 fl oz||24||14|
|MODE-OF-ACTION GROUP NUMBER1: 3A|
|COMMENTS: Will cause secondary pest outbreaks, especially spider mites, if used before hullsplit.|
|(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.|
|*||Permit required from county agricultural commissioner for purchase or use.|
|‡||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 are assigned by IRAC (Insecticide Resistance Action Committee).|