Succulent weeds (mullein plant) or those with fruits (blackberries, wild rose) or seeds (bitterbrush) support large populations of stinkbug in the spring. As these plants dry out during the summer stinkbugs move into irrigated orchard borders and then into the trees to feed on maturing fruit.
Stinkbug vs. bitter pit damage
Damage caused by stinkbugs can be confused with bitter pit damage. Stinkbug damage is usually located higher on the fruit, is conical or rectangular in shape, and ranges from very light tan to dark brown in color. Bitter pit damage, on the other hand, is distributed on the sides of the apple and near the calyx, is spherical in shape, and usually dark brown to black in color.
Cutting a cross section through the damage is the best way to differentiate between stinkbug damage and bitter pit. Stinkbug damage is caused by a long, slender proboscis piercing into the apple. The damage is conical shaped and starts right at the surface. Bitter pit damage is slightly below the surface, and tends to be more round than conical.
Stinkbugs spend most of their life outside the orchard. They overwinter as adults and become active in the spring. The females lay eggs on a wide variety of native shrubs, including wild rose, red osier dogwood, bitterbrush, and wild currents and some perennial weeds, such as mullein, mallow, and white clover. Nymphs feed on these native plants, and mature to adults in mid-July. Occasionally, stinkbugs deposit eggs on fruit trees in spring and fruit can be damaged by feeding nymphs.
While some injury to sweet cherry has been attributed to early season feeding by overwintered stinkbug, most injury to apple and cherry occurs in mid to late summer. Adults often migrate to orchards in late summer from surrounding areas in search of moisture when uncultivated vegetation starts to dry. Trees in outside rows are likely to be the most severely damaged.
2010 research has focused on improving monitoring of two species of stinkbug, the Consperse stinkbug and Chlorochroa ligata. Adult activity is first detected when spring temperatures begin to warm around bloom-petal fall. It is these adults that are reproductive, giving rise to the damaging summer population. Both species seem to peak in spring adult activity in mid-June, however Consperse stinkbugs are active over a longer period of time. Summer generation Chlorochroa are detected first (early July), and new Consperse adults appear about three weeks later. By mid to late July, summer adults of both species begin reaching damaging levels.
There are several species of stinkbugs that impact tree fruit crops in Washington. Recently, high populations of Chlorochroa and consperse stinkbugs have been reported attacking late maturing sweet cherry and apple orchards.
It can be difficult to determine when stinkbugs begin moving into orchards because they are primarily active at night and hide during the day when they detect movement. Effective stinkbug traps utilize a pheromone lure placed in a collection funnel atop a pyramid shaped platform. Stinkbugs are both attracted to the pheromone and the shape of the pyramid. Adults and nymphs will climb the pyramid and into the collection funnel in search of the pheromone source. Commercial lures can be used to monitor the consperse stinkbug. Traps may also be effective in detecting adult Chlorochroa.
Managing stinkbug populations can be difficult because they spend much of the year living on host plants outside of the orchard. Adult stinkbugs may move into the orchard in late summer and feed on fruit, both apples and cherries. When stinkbugs are detected within the orchard, the only effective means of protecting a crop is to apply contact insecticides. Pyrethroid insecticides have proven to be the most effective insecticide options for control of stinkbugs, but even a single application can be highly disruptive to biological control of spider mites and other insects. To limit the disruptive effects, targeted sprays of orchard borders are recommended. Repeated applications of a pyrethroid insecticide to orchard borders, 4 to 5 rows, has worked well to reduce fruit injury in the entire orchard. Sprays are most effective when applied at, or shortly after, dusk - the period of highest stinkbug activity. Some pyrethroid insecticides have labels for non-crop lands and can be used to treat areas directly adjacent to the orchard that have been determined to harbor high stinkbug populations.
There are a number of scelionid wasp egg parasitoids, including Telenomus podisi and T. utahensis, that parasitize stinkbug eggs and, therefore, help suppress stinkbug populations.
(PMTP Team & Mike Doerr, WSU- TFREC)