Awaiting the Aphid

By Emily Unglesbee
DTN Staff Reporter

ROCKVILLE, Md. (DTN) — An unwelcome guest spent the winter in north Texas this year — the sugarcane aphid.

The aphid usually overwinters in Mexico and the Gulf and must journey northward during the spring to infest sorghum fields. This year it overwintered as far north as the Texas panhandle, a sizeable head start for the pest and bad news for sorghum growers, Texas A&M entomologist Pat Porter warned.

"We’re expecting an intense season," he told DTN. Since its arrival on sorghum in Texas in 2013, the sugarcane aphid has spread rapidly across the southern U.S., as far north as Kansas and Illinois and as far east as the Carolinas.

The pest deals sorghum plants a double blow; it sucks moisture from them, damaging their yield potential, and also leaves behind a sticky honeydew that clogs field equipment during harvest. Under dry conditions, the pest can reproduce rapidly and colonize an entire field in a matter of days.

Last year, heavy spring rainfalls slowed the pest’s initial spread in Texas, but drier conditions later in the year allowed it to march into new territory in Kansas and southern Illinois by fall. You can see a map of the aphid’s latest conquests from Texas A&M here: http://bit.ly/….

CONTROLLING THE APHID IN 2016

Controlling the pest will be difficult for many growers this year. In the fall of 2015, EPA cancelled the registration for sulfoxaflor, the active ingredient in Dow AgroSciences’ Transform insecticide. Transform was one of only two insecticides effective against the sugarcane aphid. Its cancellation leaves most growers with only Bayer’s Sivanto insecticide to control the pest this year.

In April, the EPA granted a Section 18 emergency use exemption for Texas sorghum growers to use Transform in 2016. Other states such as Kansas have also petitioned the agency for Section 18 exemptions, and although the Texas approval bodes well for them, the EPA has not yet approved any other requests.

Entomologists have warned that controlling the aphid with only one insecticide is a surefire recipe for resistance. The aphid reproduces asexually and produces multiple generations within a season, which makes it excellent at evolving resistance to repeated use of a single insecticide.

Texas growers with access to both insecticides should plan to use both Transform and Sivanto if they make more than one application against the aphid this year, Porter said. "Every time you spray, rotate chemistry," he urged.

The temporary Transform label for Texas growers bans applications from three days prior to bloom through seed set in an effort to protect pollinators, which may also complicate application decisions.

THE LATEST ON APHID MANAGEMENT

"We’re recommending early planting this year, to outrun the aphid," Porter said. Research has also shown that neonicotinoid seed treatments can control the aphid for up to 40 days after planting, according to Louisiana State University’s management guide.

The aphid tends to inflict the worst yield losses when it infests plants in the pre-boot stage, when the valuable grain head is still developing inside the stem. As a result, threshold recommendations vary by growth stage as well as geography. Some of the most conservative instructions favor spraying if the aphid is merely present on 20% of plants in the pre-boot stage. As the plant moves into boot stage, that threshold rises to 50 aphids per leaf on 20% of plants in the field and then 30% in flowering and milk stages.

Because aphid populations can take off so quickly, scouting twice a week if the aphid is in your region is highly recommended.

For more details, see threshold recommendations for southern Texas and Gulf growers here: http://bit.ly/… and recommendations for the High Plains and elsewhere here: http://bit.ly/….

Company and university scientists have also identified some aphid-tolerant sorghum hybrids in the past two years. See the most recent information on them here: http://bit.ly/….

For more details on aphid management, see the Sorghum Checkoff’s guide here: http://bit.ly/….

Emily Unglesbee can be reached at emily.unglesbee@dtn.com

Follow Emily Unglesbee on Twitter @Emily_Unglesbee

(PS/AG)