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Sorghum Pest Alert
Thursday, July 21, 2016 2:18PM CDT

By Emily Unglesbee
DTN Staff Reporter

ROCKVILLE, Md. (DTN) -- Sorghum pests never gave Jerry Martin many headaches before last year.

Now for the second year in a row, the central Kansas farmer is bracing for infestations of the sugarcane aphid. After a slow start in Texas this year, the pest has moved north and east earlier than ever.

In Kentucky, aphids were spotted in mid-July, a month earlier than 2015. Now, three hours south of Martin's farmland near Manhattan, Kansas, the pest has been found in sorghum fields in southern Kansas 10 days earlier than last year.

The levels of infestation in those Kansas fields suggest the pest has been calling the Sunflower State home for nearly a month already, according to a report compiled by Kansas State University's field crop Extension entomology team.

"Aphid densities are well below threshold, but those with sorghum fields are encouraged to scout fields now," the team wrote.

Because they reproduce asexually, aphid populations can grow rapidly and infest fields in a matter of days.

"Sugarcane aphids have caused yield losses of 30% to 100% for sorghum growers since 2013 in many states of the U.S.," warned University of Kentucky entomologist Raul Villanueva, in a university pest alert. "Sugarcane aphids affected severely grain and sweet sorghum fields last year in Georgia, South Carolina, Missouri, Tennessee, and Kentucky."

Last year, Martin sprayed his fields in early August and still experienced yield losses when aphid-damaged plants toppled over before harvest. "We still had very good yields, but we would have had fantastic yields if so much of it hadn't gone down," he said.

The aphids are piercing insects -- they suck fluids from the plant and leave behind a sticky honeydew that encourages the growth of a sooty black fungus. The plant damage lowers yield potential and the honeydew can clog and damage combines and field equipment.

Scouting can be tedious and thresholds for treatment vary by region. Villanueva recommends selecting 10 plants by random within a 50-foot stretch of the field. Examine a top and bottom leaf from each plant, looking for the tiny, light-colored aphids and counting those you find.

After repeating this process four to five times, count the average aphid counts per leaf. "If this average is between 30 to 135 aphids per leaf up to boot stage of development, then make an insecticide application," Villanueva concluded.

Growers on the High Plains should follow this slightly more conservative threshold: http://bit.ly/….

For more details on how to weigh the cost and potential benefits of spraying, see this guide from Texas A&M: http://bit.ly/….

Growers have two options for effective treatments this year: Bayer's Sivanto Prime insecticide and Dow's Transform insecticide, which has received Section 18 emergency use approvals for sorghum fields in 14 states (Alabama, Arkansas, Georgia, Kansas, Louisiana, Mississippi, Missouri, North Carolina, Nebraska, Oklahoma, South Carolina, Tennessee, Texas and Virginia). You can find those labels here: http://transformmysorghum.com/….

The EPA also just issued a Section 18 emergency use approval for Bayer's Sivanto Prime in sweet sorghum in North Carolina. You can see that label here: http://bit.ly/….

You can find the Kansas State University sugarcane aphid alert here: http://bit.ly/…, and Villanueva's update from Kentucky here: http://bit.ly/….

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

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.


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