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Stink Bug Management: a research update
By Christian Krupke, WSU-TFREC, Wenatchee, WA
History and description of the pest
Stink bugs have been increasing as a pome fruit pest for approximately ten years in many fruit-growing areas
of north-central Washington. There are several species of stink bugs commonly found in and around orchards,
but the key pest species appears to be the consperse stink bug. The consperse stink bug is approximately 3/8"
long as an adult, drab brown in color, with alternating off-white and black colored squares along its lateral
margin on the back half of its body. There are several other stink bug species capable of causing fruit damage;
however, the consperse stink bug is responsible for the vast majority of reported damage and all research findings
detailed below are confined to this species.
Diagnosis of a stink bug problem: Stink bug vs. Bitter pit
Stink bug damage superficially appears very similar to the nutrient deficiency known as bitter pit, and correct
diagnosis is key in making subsequent management decisions. The first thing to note is the time of year when
damage is noted. Stink bug damage is first apparent in mid to late-July, generally increasing in severity right
up until harvest. Bitter pit symptoms often appear earlier in season. Both stink bug damage and bitter pit
appear as darkened, sunken areas on the fruit surface. However, stink bug damage is most frequently confined
to the shoulder area (the bugs feed while hiding in the stem bowl) and the top one-third of the apple, while
bitter pit is more apparent on the lower half of the fruit, especially near the calyx. The next step in damage
diagnosis is cutting the damaged section to view it in cross-section. This is accomplished by cutting directly
through the center of the damaged section, then making a second cut perpendicular and bisecting the first so that
a wedge or triangle that can be removed. This will allow viewing of the damaged area in cross-section, exposing
the differences in damage symptoms. Stink bug damage is generally conical in shape, with the light brown damaged
area widening toward the skin of the apple. In contrast, bitter pit damage is generally circular in shape, and
often may not extend all the way to the skin. Bitter pit is dark brown or almost black in mature fruit, whereas
stink bug damage ranges from off-white to a medium brown color. Stink bug damage is usually greater on the borders
of orchard adjacent to native habitats and is found on trees with both heavy and light fruit set. Bitter pit can
usually be found throughout an orchard and is most common on trees with low fruit set. Finally, if stink bug is
suspected as the culprit, catching the bugs in the act is the next step. This is most easily accomplished at or
shortly after dusk, or early in the morning. Bugs will be found feeding while hiding in the stem bowl or in the
sheltered areas between fruit and leaves.
Pheromone-based monitoring
A successful system of monitoring for presence/absence or relative numbers of stink bug is essential if we are to
manage this pest successfully. We have worked with an aggregation pheromone for the past three seasons, and have
found this pheromone attracts large numbers of both male and female adult bugs when placed on host plants, especially
mullein. It is attractive to adults both during the initial mating period (April-June) and in the late summer when 'new',
non-reproductive (but fruit-feeding) adults are present (late July-early September). While we are able to attract large
numbers of bugs to baited mullein plants, the most difficult step in monitoring has been developing a trap to actually
retain bugs, and this remains an ongoing research effort. An important discovery is that the vast majority of aggregation
activity occurs at dusk, so any observations of aggregated bugs or insecticide treatments (more on this below) should be
conducted at dusk or slightly thereafter. Although bugs can also be seen during daylight hours, we have found that these
numbers represent only 10 to 50% of the nighttime totals.
Commercial lures has been developed and field-tested for stink bug monitoring and at least one should be available in 2003.
Stink bug management: In-orchard control options
Chemical control of stink bugs in the orchard has been difficult because stink bug invasions occur late in the growing
season, limiting the number of insecticides that can be used due to pre-harvest interval restrictions. In addition, there
is a lack of solid information on what time of year the bugs are actually present in the orchard. To ensure proper timing
insecticide treatments should not be applied until the first signs of damage are seen and confirmed as being caused by
stink bug, as outlined in the section above. The first damage will usually be found on orchard borders in mid to late July
in the highest pressure areas, usually adjacent to native habitats. Although Carzol has been recommended as an in-orchard
treatment, only one post-bloom application of this material is permitted and then only when specific written recommendations
from a certified pest control advisor are obtained. We have conducted insecticide screening tests with a variety of
products, ranging from established products to some of the newer, 'soft' chemistries. A product that has looked promising
is Danitol, a synthetic pyrethroid. However, this product has significant non-target effects, and in particular has been
shown to cause flare-up of pest mites due to its negative impact upon beneficial mite species. We are currently conducting
trials to determine the severity of these non-target impacts, in order to evaluate the possible role of Danitol as part of
a management plan for stink bug. One possible alternative to whole-orchard treatments is treatment of the border rows
only, or alternating treated/untreated rows in order to preserve a reservoir of predatory mites.
Aggregate-and-kill
We have conducted a number of experiments to investigate the possibility of using the highly-attractive pheromone in
combination with host plants, in an aggregate-and-kill strategy. In these tests mullein plants were baited with lures
with stink bug pheromone at intervals of 20 feet along orchard borders beginning in mid-April (the onset of the mating
period). These baited plants were sprayed using a backpack-sprayer to apply an insecticide (Carzol) early in the morning
at weekly intervals throughout the mating period, or until early July at which point all baiting and spraying activities
ceased. Although these early season bugs did not represent a direct threat to the orchard (they die after mating),
they do represent the parents of the bugs that will invade orchards in late summer, and we wished to reduce this breeding
population as much and as early as possible to impact mating/egg-laying. This treatment was evaluated by comparing stink
bug fruit damage in baited and sprayed blocks vs. unbaited and unsprayed checks in a total of four orchards. The results
were encouraging; stink bug damage was reduced by over half in the border rows of the treated areas (8.2% damage vs.
3.7% damage). This presents a highly-selective, low-input alternative to the spraying of orchards, but it is important
to note that this treatment is not yet refined to the point where it is applicable to all situations. Our current
system is dependent upon mullein plants as a 'trap crop'; a lure placed on inanimate objects or non-host plants will
initially attract - but not retain - stink bugs. Not all growers with stink bug problems have mullein growing on
borders, so we hope to find a synthetic lure or other attractants that may act as an "artificial plant" in retaining
stink bugs so that insecticides can be applied.
Christian Krupke is a doctoral candidate working with Dr. Jay Brunner at the WSU-TFREC in Wenatchee. He received his
Masters in Entomology from Simon Fraser University in Vancouver, B.C. He is known for his keen wit, culinary skills and
devotion to stink bug research. He welcomes your inquiries at ckrupke@wsu.edu.
Contact Us
Ted Alway, Coordinator Areawide II
Phone: 509-663-8181 x268
E-mail: alway@wsu.edu)
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