Brown Stink Bugs in Arizona Cotton

Under the Radar, Deep in the Canopy

Brown Stink Bugs in Arizona Cotton

Peter C. Ellsworth, Lydia Brown & Ayman Mostafa

PDF Version available at: http://ag.arizona.edu/crops/cotton/agronomic_ipm.html

A) Brown Stink Bug (BSB)

The Brown Stink Bug (Euschistus servus) (BSB) (A) is rarely damaging in Arizona cotton, but at high densities, they can reduce yield and quality. BSBs pierce bolls to feed on developing seeds; young bolls (<10 d old) (B) may shed when these are the only sizes available to the bugs (C). BSB can cause carpel and seed injury (D), stain lint, lower yields and quality, and encourage boll rot organisms. Successfully attacked bolls will have callus warts (E) on the interior of the carpel wall or brown stains on lint (F) 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.

B) Small bolls shed during very early fruiting

   There is no recent Arizona-specific information available for monitoring or decision-making. We must rely on information from the Southeastern U.S. Stink bug action thresholds are based on the percentage of internally damaged bolls (bolls with any internal injury). Collect at least 25 1-inch bolls from each field, avoiding 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.

Boll sizes for stink bug sampling

Crack and inspect bolls for internal injury. If any warts or stained lint are present, count that boll as injured. Chemical control may be warranted when 20% 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, because cotton’s susceptibility to stink bugs varies. Very early and very late in the season, stink bugs do not pose as much of a threat and higher percentages of injured bolls can be tolerated, up to 50% 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.

C) Damage to young bolls (1–10 days old) may cause shed

D) Damaged 1 inch diameter boll

E) Callus warts from on the carpel interior (similar to pink bollworm injury)

F) Stink bug feeding injury can result in stained lint

   Research in Arizona as far back as the 1950s confirms that stink bugs are not caught in representative numbers in standard sweep net sampling, because they 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 to assess chemical controls.

   There have been no BSB specific chemical control studies since the early 1960s, when BSB was often associated with alfalfa production. So we must rely on the Southeast; however, even there, most chemicals are screened against a complex of unrelated stink bugs (Green Stink Bug & Southern Green Stink Bug). Lab bio-assay results for BSB show that Bidrin is highly effective (Fig. 1). 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 1 lb ai / A 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.

Figure 1. Topical BSB lab insecticide efficacy (% at 24 hr) in Arkansas (bars) & Field efficacy (% 2–4 DAT) in Georgia against Euschistus spp. (dots ± SEM); adapted from Greene et al. 2005, Proc. Beltw. Cotton Proceedings & P. Roberts, unpubl. data. *Endigo at 4–5.5 oz. Products and lbs active ingredient per acre tested shown on left; chemical classes shown on right.


Special thanks to Drs. Phillip Roberts (Univ. of Georgia) and Jeremy Greene (Clemson University) for permission to use their data in Figure 1 and for comments on earlier drafts.

Any products, services, or organizations that are mentioned, shown, or indirectly implied in this publication do not imply endorsement by the University of Arizona.

Also see:

Bacheler, J. et al. 2010. http://ipm.ncsu.edu/cotton/insectcorner/pdf/AG_730_WPrint-NC.pdf

Herbert, A. et al. 2010. http://pubs.ext.vt.edu/444/444-390/444-390_pdf.pdf

Proper Timing for Final Lygus Sprays

To Stop or Not to Stop, That is the Question

A Guide to Terminating Lygus Controls

Peter C. Ellsworth, Lydia Brown (University of Arizona) & Steven Naranjo (USDA-ARS)


PDF Version available at: http://ag.arizona.edu/crops/cotton/agronomic_ipm.html

Making the best decisions about stopping chemical controls is knowledge intensive. Using information about your specific situation, sound decisions can be made about when to safely cease chemical control of Lygus bugs. These guidelines are based on 4 years of replicated research and limited validation on grower fields. They should help facilitate the grower – PCA dialog that is needed to arrive at the best decision for each individual grower’s set of production conditions.

   Thresholds for Lygus bugs in cotton have been well-established for years and validated on commercial acreages in Arizona. When a field has reached a minimum threshold density of 15 total Lygus with 4 nymphs per 100 sweeps (15/4) any time during the majority of the primary flowering period, a spray should be made and should return more than the cost of that spray to the grower in yield protected. Certain conditions (e.g., ample natural enemies) permit initial action thresholds of up to 15/8. However, as a crop slows in growth and blooming rates decline, the amount of yield that can be saved by any given Lygus spray is reduced to a point of diminishing returns. These guidelines are designed to help a grower and PCA decide when the final Lygus control should be made to give the best economic return. A grower and PCA will need to know at least four things before they can make this decision properly:

Key Factors in Decisions about Terminating Lygus Controls

1.Planting date (optimal/early vs. late),

2.Maturity class of the variety (early-, medium-, or full-season),

3.Production goals relative to irrigation termination plans. “Optimal” irrigation termination is timed to grow and mature the primary fruit set only. Some growers elect to extend irrigations for a variety of reasons. So “later” irrigation termination timing usually consists of one or two additional irrigations beyond that necessary to mature the primary fruit set.

4.Cotton development determined by nodes above first position white flower (NAWF).

   Choose the production scenario (line) that best represents your situation based on planting date, maturity class, and irrigation plans. Then, if Lygus thresholds are exceeded, make your last spray when your revenue is significantly increased (denoted by ‘$’). Sprays made later than this will unlikely return your investment.

Choose chart that best matches your planting, ‘Early’ or ‘Late’

              

Select the line color of the maturity class of your variety, Full, Medium, or Early

* Irrigations extended

Choose the shade of color that best matches your irrigation plans, normal or ‘extended’

         

Make your last spray when your revenue is significantly increased, as indicated by ‘$’ on your chosen line

Figure 1. Revenue lines for 12 different production scenarios based on planting date, variety, and irrigation termination plans. When Lygus thresholds are exceeded (15/4), make your last spray based on nodes above white flower (NAWF) for your specific production scenario, as indicated by the ‘$’ sign. Lygus sprays made later than this will not produce significant increases in revenue.

U = no sprays made for Lygus control.

This dynamic guide shows results for only one set of economic conditions: cotton lint = $0.75 / lb; $12 / late season irrigation; $17 / Lygus spray.

Also see:

Ellsworth 2001. Lygus In Cotton: Implementing Action Thresholds. UA Lygus in Cotton Series No. 3. http://ag.arizona.edu/crops/cotton/insects/lygus/lygus3.pdf

Ellsworth et al. 2011. $1+ Cotton? New Thresholds?! UA IPM Short. http://ag.arizona.edu/crops/cotton/files/NewThresholdsVF.pdf