By Peter Ellsworth, Lydia Brown, and Ayman Mostafa – University of Arizona
The brown stink bug (BSB), Euschistus servus, rarely damages Arizona cotton but the insect can reduce yield and quality at high densities.
The insect pierces the boll to feed on developing seeds. Bolls less than 10-days-old may shed when these are the only sizes available to the insect.
BSB can cause carpel and seed injury, stain lint, lower yields and quality, and encourage boll rot organisms.
Successfully attacked bolls have callus warts on the interior of the carpel wall or brown stains on lint and seeds.
An externally visible small brown pockmark on the boll surface does not necessarily mean the boll interior is damaged. Bolls must be opened to determine if injury has occurred.
There is no recent Arizona-specific information available for BSB monitoring or decision making. The Arizona cotton industry relies on information from Southeastern U.S. stink bug action thresholds based on the percentage of internally damaged bolls (bolls with internal injury).
Collect at least 25, one-inch bolls from each field and avoid the field edges. The boll sample must consist of properly-sized bolls which give easily when squeezed and are 0.9–1.1 inches in diameter.
Crack and inspect the boll for internal injury. If any warts or stained lint are present, count the boll as injured.
Chemical control may be warranted when 20 percent or more of the boll sample have warts or stained lint and stink bugs are present in the field.
The Southeast has developed dynamic thresholds for stink bugs since cotton’s susceptibility to stink bugs varies. Stink bugs do not pose as much of a threat very early and very late in the season. Higher percentages of injured bolls can be tolerated; up to 50 percent with warts or stained lint.
Maturing bolls are relatively safe from stink bug feeding injury starting at 25 days of age or once they are ≥1.25 inches in diameter. Internal injury to lint is unlikely.
Research in Arizona as far back as the 1950s confirms that stink bugs are not caught in representative numbers in standard sweep net sampling since the insects drop rapidly from plants and are frequently located on the plant below the range of a normal net stroke.
Do not rely on sweep net sampling alone, except to confirm BSB presence in the field. Small boll sampling is required to schedule and assess chemical controls.
There have been no BSB specific chemical control studies since the early 1960s when BSB was often associated with alfalfa production. The Arizona industry must rely on Southeast information. However, even there, most chemicals are screened against a complex of unrelated stink bugs (green stink bug and southern green stink bug).
Lab bioassay results for BSB show that Bidrin is highly effective. Though a standard there, this old organophosphate is not registered for use in Arizona. Bidrin is significantly more effective on Euschistus spp. than bifenthrin (Capture), but not more so than acephate (Orthene). Acephate at the full label rate of one pound per acre may provide control of BSB.
Belay is an option for helping suppress stink bug populations in general but should not be relied on as a rescue tool.
Few other products are effective.
For the UA graphs associated with this article, click this link for the PDF:
http://ag.arizona.edu/crops/cotton/files/BrownStinkBugShortvF.pdf.
The URL, mobile-friendly link is:
http://apmc-ipm-shorts.blogspot.com/2012/08/underthe-radar-deep-in-canopy.html.
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