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Released: July 20, 2007

Potentially Damaging Soybean Aphids Again Found in Kansas

MANHATTAN, Kan. – Soybean aphids, which have the potential to wreak havoc in soybean fields, have again arrived in Kansas.

This year’s soybean aphids were first discovered July 12 in a research plot by Kansas State University plant pathology leader Doug Jardine and Lyon County agricultural Extension agent Brian Rees.

The plot is a sentinel plot, used to monitor the possible occurrence of soybean rust and soybean aphids. Both are potential threats to the state’s soybean crop, according to Extension entomologist Jeff Whitworth.

Five days after Jardine and Rees’ discovery, soybean aphids were found in Riley Co.

“These are the first 2007 reports of soybean aphids in Kansas. They’re somewhat earlier than in past years, although approximately in the same time frame as seen in 2005,” Whitworth said. “But, populations that year never really became troublesome.”

The soybean aphid, Aphis glycines, was first detected in the United States in 2000 and first detected in Kansas in 2002.

“We have had soybean aphids every year since, but only in 2004 did they become a problem of economic consequence, requiring some fields to be treated with insecticides,” Whitworth said. “In fact, only one county had verified soybean aphid populations in 2006.”

Entomologists Carol Pilcher, Marlin E. Rice and Todd Vagts of Iowa State University released an ISU research-based Extension publication in 2005 that stated:

“This pest has the potential to cause approximately 3 million acres to be sprayed and to cause losses of more than 55 million bushels, meaning an economic impact of more than one-quarter billion dollars in an outbreak year. These results reinforce the need for scouting to accurately determine the soybean aphid populations in your fields and emphasize the use of current threshold recommendations to justify the costs of applying insecticides. These steps are key to saving dollars in the management of soybean aphids.”

More about the ISU study is on the Web at: http://www.ipm.iastate.edu/ipm/icm/node/53.

Soybean aphid populations seem to be sensitive to hot temperatures -- specifically temperatures over 95 degrees, K-State’s Whitworth said.

High summer temperatures may not actually kill the aphids, but it does seem to drastically reduce their ability to reproduce, he said. And, if they are not rapidly reproducing, this gives some of their natural enemies, such as predators and parasites, the opportunity to help regulate the aphid populations.

Aphid populations can increase very quickly because they reproduce parthenogenically, he said. This means they don’t have to mate and lay eggs. Each aphid is a female and thus produces females that produce females and so on, without any lag time of looking for mates and waiting for eggs to hatch. They are born and start feeding and producing young immediately.

Soybean aphids are the only North American aphids to colonize and develop large numbers on soybeans, Whitworth added. They’re relatively small, light-green aphids with distinctive black cornicles or “tail pipes” at the tip of their abdomen. Infestations usually start at the outer canopy on newer soybean leaves. Aphids can be throughout the canopy, but well-established populations most often will be on the undersides of leaves and on stems and developing pods.

“This aphid can transmit many viral diseases, but it also can stress plants and reduce yields by virtue of their feeding, which removes nutrients from the plant,” the entomologist said. Infested plants may have a distorted, yellow appearance and may become covered with a slick, sticky substance called “honeydew” -- which itself often becomes dark and sooty, due to molds living on the honeydew. Ants seem to be attracted to this honeydew, so “if you see ants in your soybean canopy, that may be an indicator of an aphid infestation,” he said.

The aphid populations discovered in Kansas so far are small and widely scattered, Whitworth said. However, this year’s soybean crop in general is a little late in development, and that might make it more vulnerable to insect damage.

In its July 16 weekly report on crop conditions, the Kansas Agricultural Statistics Service said 38 percent of the soybeans statewide were blooming. This put the crop well behind the 63 percent blooming at the same time last year and the 46 percent five-year average.

Soybeans in the late vegetative and early reproductive stages are probably the most susceptible to aphid feeding, Whitworth said.

States with annual soybean aphid problems have set the economic thresholds for applying controls at around 50 aphids per plant in pre-reproductive plants and about 250 per plant in the R1 (beginning bloom) to R4 (full pod) stages. The thresholds take into account a seven-day lag between scouting and treatment, for time to make the arrangements to treat, he said.

Whitworth is encouraging producers who find a soybean aphid infestation to report it to their county or district K-State Research and Extension office.

In addition, Extension offices have information about sampling, a new technique called “speed scouting,” treatment thresholds, and insecticides registered for use against soybean aphids. More information also is available on the Kansas Extension Web site: http://www.entomology.ksu.edu/DesktopDefault.aspx?tabid=668.

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Mary Lou Peter-Blecha
mlpeter@oznet.ksu.edu
K-State Research& Extension News

Additional Information:
Jeff Whitworth is at 785-532-5656.