How to Manage Pests
UC Pest Management Guidelines
A variety of plant bugs in the family Miridae attack pistachio. The particular species varies depending upon location and natural vegetation. All of these bugs have a small, triangular-shaped marking on the back.
Neurocolpus adults are straw colored, slightly hunched, and about 0.3 inch in length. They often overwinter as eggs—at the base of buds or leaf-petiole scars—on 1-year-old pistachio wood. The nymphs are greenish in color with brown markings on the back. Both stages are easily identified by the relatively long, hairy first antennal segment and brown and white bands on legs and antennae. Although Neurocolpus have been found only in orchards near California buckeye and Rhamnus spp., the native hosts for Neurocolpus, once established in a pistachio orchard, Neurocolpus will overwinter there.
Lygus bug adults are about 0.25 inch in length, and coloration varies from brownish to green. Lygus has a yellowish, triangular-shaped area on the back between the wings. They are most commonly found near alfalfa and beans, or plants such as clovers, Russian thistle, tarweed, London rocket, and lupine. Lygus usually migrate into a pistachio orchard from nearby weeds. When rainfall and spring temperatures are ideal for the growth of broadleaf weeds, Lygus populations can be severe. When Lygus moves into the orchard, they tend to locate in the cover crop and move into the trees when the cover crop becomes unsuitable.
Calocoris adults are about 0.25 inch in length with a green-colored body. The wings have a reddish brown tint and are black where they overlap. There are also two black dots on the thorax. Calocoris is usually found on mustard, wild radish, and vetch hosts and is most common in the northern San Joaquin and Sacramento valleys. Calocoris does not overwinter in pistachio trees but migrates into the orchards as native weed hosts dry or are cultivated in spring.
Phytocoris overwinters in the egg stage on one-year-old fruit wood on pistachios as well as on other deciduous trees. Adults are about 0.25 inch long and are predominantly gray with flecks of black and white; they have long antennae and legs and can move rapidly when disturbed. The nymphs are also gray with white bands on the legs and antennae. Moderate populations of Phytocoris are not considered damaging and seldom require treatment. They are predators of other insects, especially immature soft scale in March and April and second-instar scales that are migrating from leaves to woody shoots in fall; they also feed on navel orangeworm eggs in spring.
The least common of these plant bugs is Psallus vaccinicola. The adults are about 0.13 inch long and are brownish red in color. They have been found predominantly near oaks in the Sacramento Valley.
These bugs are only damaging for a short period of time, from bloom (early April) through shell hardening (late May). They insert their mouthparts into the nut, causing damage known as epicarp lesion. This damage is done before shell hardening and, except for damage caused by Neurocolpus, is more random in occurrence than damage caused by leaffooted plant bugs and stink bugs. Damage to small nuts results in blackening and nut drop. As the nuts enlarge, the hull tissue turns brown and necrotic, and the outside will often become sunken. On the inside of the nut there will be a small black spot or irregular-shaped pit in the area where the bugs fed on soft shell tissues.
Careful attention to vegetation in and around orchards is the key to effective management of plant bugs. The general pattern of bug appearance and distribution in an orchard is that Phytocoris overwinters in the trees, and if Neurocolpus is present, it too may overwinter in the trees. Calocoris and Lygus overwinter on preferred weed hosts in the ground cover. As vegetation in the pistachio orchard or surrounding areas dries, these bugs can move into the orchard canopy where they damage the developing crop. Options to consider are (1) elimination of all herbaceous vegetation; (2) maintenance of monitoring strips; (3) use of trap crops with chemical treatment; and (4) use of cover crops that are not attractive to pest insects. Success or failure with each option will likely depend on the specific site and the species of bugs in the orchard.
Organically Acceptable Methods
Monitoring and Treatment Decisions
There are currently no guidelines based on the number of plant bugs found. If populations are found uniformly throughout the orchard after bloom, initiate treatment. If insect numbers are low in the trees (three or less per ten beats would be considered low), but Lygus and Calocoris are present in the ground cover, consider just treating the ground cover. If Lygus and Calocoris move into the trees from drying vegetation, they (as well as Phytocoris) can cause damage into early May but cannot penetrate the hardening shell after that. Neurocolpus can also be a problem in May if it is established in the orchard or migrates in. By early June or after the shell has hardened, these insects are no longer damaging.
UC IPM Pest Management Guidelines: Pistachio