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Areas Infested with Soybean Aphids Expanding

August 7, 2003

Reports of soybean aphid activity are still coming in. In fact, reports are indicating that the problem area is no longer limited to northeastern Illinois. Several people have called in with economic infestations in northwestern Illinois and northeastern Iowa. Kevin Black, Growmark, has received word of infestations near Jerseyville (20 miles north of St. Louis) and Beardstown (70 miles southwest of Peoria). Overall, densities are still the highest in northern Illinois. Rod Winter, FMC, is finding 500 to 1,000 aphids per plant in fields in Lee, Ogle, and Winnebago counties. Chet Hetrick, FMC, sent these per-plant counts of soybean aphids: Manteno, 250 to 400; Kankakee to Rte. 24, 150 to 200; Rte. 24 to Rte. 9, 50 to 100; Rte. 9 to I-74 (Ogden), 25 to 100. Although 25 to 100 soybean aphids per plant does not necessarily meet the recommended thresholds for treatment, fields need to remain under watch, as densities can increase up to 10-fold in just 1 week. As soybean aphids are being found in more central and southern areas of the state, keep in mind these recommendations for insecticide applications when scouting:

  1. a density of 25 or more aphids per leaflet (also monitor for natural enemies)
  2. an increase in pest numbers from the first to second sampling period
  3. alatoid (winged) nymphs make up less than 50% of the population
  4. soybean stage is R1 or R2

For more information on soybean aphids, please refer to the soybean aphid update from issue no. 17 (July 18, 2003) of the Bulletin.--Kelly Cook

Author: Kelly Cook

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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