Multi-state research and Extension effort targets crop-jumping pest

Thursday, September 1, 2016

It is a growing problem across an increasing area of the southern United States: Sugarcane aphids discovering sorghum is an equally yummy crop to infest.

The switch was first noticed widely in 2013, with significant sorghum yield losses occurring in Texas, Louisiana and Mississippi. That same year, the aphids switch to sorghum was noticed in Oklahoma, though with far less significant – but still disturbing – yield loss.

“We only found aphid infestations in sorghum in one county in 2013, but it was clear we needed to prepare for what was likely coming our way,” said Tom Royer, Oklahoma State University Cooperative Extension Integrated Pest Management coordinator. “By 2015, we found the sugarcane aphid in 27 counties, infesting a minimum of 200,000 acres statewide.”

Sugarcane aphids can be extremely damaging to sorghum grown for grain and forage, and are capable of increasing into large numbers quickly. It is not uncommon to find thousands of aphids per field.

“The aphids damage plants directly through their feeding, sometimes killing leaves outright if the infestation is significant enough,” said Ali Zarrabi, a researcher with OSU’s IPM team. “They also damage plants indirectly by coating leaves and seed panicles with honeydew which serves as a substrate for sooty mold and ultimately interferes with harvest operations, adding to operational costs that most producers can ill afford.”

In 2013, the sugarcane aphid infestation zone extended across nearly 2 million acres of grain production in four states. The zone rapidly expanded to nearly 3.2 million acres across 12 states in 2014.

Oklahoma farmers and ranchers plant between 300,000 and 400,000 acres of sorghum annually. The state ranks fourth nationally in the production of sorghum grain and eighth nationally in the production of sorghum silage, according to data from USDA National Agricultural Statistics Service.

But Okies are never one for ignoring a challenge, especially when the signs are obvious a change is in the wind. At the first hint of a growing problem in 2013, the Oklahoma Sorghum Growers Association contacted OSU’s Division of Agricultural Sciences and Natural Resources.

“They initially requested our support for an emergency Section 18 registration from the Environmental Protection Agency to allow producers to use sulfoxaflor as a control agent,” Royer said. “In addition, the Sorghum Checkoff Program funded five research and Extension demonstrations to evaluate chemical and varietal control options and the impact of the aphid on sorghum production.”

Based on the results of the division demonstration plots, an uncontrolled infestation of sugarcane aphids reduced sorghum yield by an average of 18 bushels per acre. Sulfoxaflor was applied to more than 150,000 acres of grain sorghum in 2015.

“Demonstration plots coordinated by the division’s IPM team indicates this emergency registration saved Oklahoma sorghum growers somewhere between $7.2 million and $14.4 million in total lost grain yield, depending on whether an individual producer sprayed his or her crop once or twice,” Royer said.

The ongoing battle against the aphid incursion did not end there, however. Royer and cooperating scientists from four other states were jointly awarded a $298,000 competitive grant from USDA’s National Institute for Food and Agriculture’s Crop Protection and Pest Management program to develop a sampling program for sugarcane aphids aimed at saving producers time and money.

While there was an obvious initial need to develop a coordinated set of insecticide efficacy trials, it was during the 2014 growing season that discussions arose regarding the efficacy of insecticides for control – most currently registered insecticides were found to provide poor control – and, equally important, when to treat a field because of the aphids ability to rapidly increase in numbers.

“It was clear we needed to develop and get into the hands of sorghum growers a research-proven, efficient and user-friendly sampling system that allows for an accurate assessment of aphid density in a field and a rapid determination that a threshold treatment has been reached,” Royer said.

And the sooner the better, for by 2014, official estimates were that that 100 percent of sorghum acres in Louisiana were infested, 90 percent of acres in Arkansas, 60 percent of acres in Texas and up to 15 percent of sorghum acres in Oklahoma.

“Research conducted by a team led by one of our cooperating partners, Dr. Robert Bowling of Texas A&M University, and published in 2015 suggested the sugarcane aphid can cause up to 60 percent yield loss if left uncontrolled,” Zarrabi said. “In extreme cases, uncontrolled infestations in the pre-boot stage can prevent head emergence and lead to a complete loss of grain yield.”

The conservative assessment of the potential economic impact of uncontrolled infestations was estimated to be $41.5 million in lost grain sales in Arkansas, Louisiana, Oklahoma and Texas, using USDA data to set a grain market value of $4 per bushel and a projected harvest of 179 million bushels.

“We’ve been sponsoring research for the past two years and this team of collaborating scientists has really stepped up, shifting a good part of their time and attention away from other activities to tackle what has been something of an emergency need,” said Brent Bean, United Sorghum Checkoff Program director of agronomy. “This team is comprised of some of the nation’s top professionals in the fields of entomology, agronomy and plant pathology. To be able to call upon that level of expertise is exactly what U.S. sorghum growers needed.”

Project coordinators for the grant are Royer, Bowling, Norm Elliott of USDA, Allen Knutson of Texas A&M AgriLife, Nick Seiter of Arkansas Extension, Sebe Brown of Louisiana State University and Brian McCormack of Kansas State University.

Royer said the cooperating states engaged in developing the needed sampling system encompass a region where sugarcane aphids can overwinter, as well as areas where the establishment of the pest depends on migration from overwintering regions.

“By characterizing the establishment of resident and immigrating populations of the aphid in sorghum over multiple years, we will develop a sampling plan that is usable across all sorghum-producing areas,” he said. “Once this tool is developed, it will allow a user to selectively manage sugarcane aphids with maximum impact on yield preservation and economic return, as well as minimal impact on environmental disruption.”

In addition to the sampling tool, Oklahoma’s “Sugarcane Aphid Team” is conducting research to identify effective insecticides, resistant sorghum varieties, the best cultural practices to avoid and/or mitigate infestations and improved decision-making tools for producers.

The Oklahoma team officially consists of Royer, Zarrabi, Kelly Seuhs, Kristopher Giles, Josh Lofton, Tracy Beedy and Jessica Pavlu – all with OSU’s Division of Agricultural Sciences and Natural Resources – and USDA researchers Elliott and Scott Armstrong. Additional DASNR researchers and staff also contribute to the ongoing sugarcane aphid and sorghum research efforts.