In 2011, the telephone in the Arizona Pest Management Center at the University of Arizona (UA) started ringing. Farmers and pest control advisors (PCAs) from Central Arizona and along the Colorado River on the Arizona-California border were reporting elevated levels of brown stink bugs (BSB) in Upland cotton.

“We’ve had them in our area for at least 100 years, but haven’t had a major outbreak since 1963,” explains Lydia Brown, assistant for Extension, Agronomic Crops IPM, and a Master’s student in Entomology and Insect Science, under the tutelage of Peter Ellsworth, UA IPM specialist.

BSB, a seed-feeding insect, pierces immature bolls causing damage which can lead to boll shed, and a reduction in yield and quality.

Contamination of cottonseeds from aflatoxin, produced by a fungus that enters through the feeding sites of pierced bolls, could cause even further economic losses – especially when cottonseed prices are hovering in the $300 a ton range and Arizona’s cotton acres are estimated to increase more than 50 percent this year.

Chemical efficacy trials

Brown soon decided to focus her graduate research exclusively on this escalating problem. From 2012-2013, she conducted chemical efficacy trials on commercial farming operations in Central Arizona.

Her on-farm trials raised more questions than delivered answers and implied that the benefits from BSB management attempts increased problems and costs associated with other pests. Brown continued her experiments at the UA’s Maricopa Agricultural Center (MAC) in 2014 and 2015.

Her findings from those experiments verified that bolls were most susceptible to damage within the first four to six days of feeding. Also, young bolls sustained more damage.

Bidrin and other chemistry

In trials to evaluate potential chemistries for control, none provided the efficacy needed. Bidrin, an effective chemistry for BSB control used in the Southeast, only managed a 40-50 percent mortality rate in her controlled feeding experiments.  

“It could have had something to do with the difference in the genetics of the BSB in our area, but we’re just not sure at this point,” Brown says. “We didn’t have any labeled products available that had the efficacy we needed for adequate control.”

The products used - organophosphates and pyrethroid insecticides - disrupted the overall integrated pest management (IPM) program, while also negatively impacting non-target organisms including big-eyed bugs, important predators of whitefly, mites, and lygus bugs.

So, Brown asked for help from Phillip Roberts and Michael Toews with the University of Georgia. They replicated research already conducted in the Southeast since the climate and pest complexes in the Western cotton region are so different.

Brown says growers have been requesting spray thresholds, but that has not been possible since researchers do not have definitely effective insecticides, nor quantified effects of those BSB sprays on other pests.

Any yield or quality gains from BSB control could be zeroed out by the added costs of managing outbreaks or resurgences of other pests.

BSB economic analysis

With financial assistance from the Western IPM Center, Brown conducted an economic analysis of BSB management. Field trial results showed no benefits in yield, gains in seed quality, or reductions in aflatoxin levels from BSB treatments.

Some collateral control of lygus was gained with Orthene, but there are more “selective” (and therefore preferred) alternative chemistries for lygus management.

The economic analysis also confirmed they spent more money and sprayed more times in response to pest resurgences and secondary pest outbreaks where BSB sprays were made. There was also a 33 percent increase in risk for spraying mites, plus a 33 percent increase in risk for sprays for whiteflies where BSB sprays were made.

“These extra sprays increased our management costs of whiteflies and mites by $16.30 an acre; in addition to the $72 an acre spent attempting to control the BSB. This was also revealed in a year when lygus and whitefly pressures were at historic lows at the MAC location,” adds Brown.

Under more normal pest pressures, Brown would expect even greater costs associated with more intense pest resurgences.  

Past control to the present

Over the last 20 or so years, Southwestern pest management has improved from an unstable system that relied on broad-spectrum insecticides, often triggering secondary pest outbreaks and resistance development, to one relying on research-based, field-verified thresholds, improved sampling methods, and the use of selective insecticides.

Prior to the resurgence of the BSB, Southwestern producers had reduced spray applications by almost 90 percent, control costs by over 80 percent, and insecticide use by 77 percent.

Well-established lygus thresholds and the use of selective insecticides allowed beneficial insect populations to thrive, and conservation biological control (bio-control) to be more effective. This not only helped to control lygus (the most yield-limiting pest to Western cotton production), but also whiteflies and mite populations.

“There continues to be inquiries about the economic benefits of brown stink bug control efforts,” says Brown. “Early data on the efficacy of those products that have been used, many of which have proven ineffective, is inconclusive. In some cases where control was seemingly achieved, we didn’t see significant increases in yield.”

Future BSB control

As Brown and other researchers move this project forward, growers in Arizona, the Imperial and Riverside counties in California, and tribal lands within the Gila, Ak-Chin, and Colorado River Indian communities, will probably base future control decisions on these research recommendations.

Peter Ellsworth says, “This entire region, including tribal communities, benefit collectively from cotton grown on their lands. We have formed close relationships with growers and the PCAs who serve them.”

He adds, “We want our economic analysis to encompass all important aspects of an IPM program, including bio-control.”

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