This year, soybean aphids were first detected by Dr. Greg Roth and his crew on June 17 in his soybean variety test at the Russell E. Larsen Agricultural Research Station near Rock Springs, PA. Their observations were verified by Dennis Calvin, Field Crop Specialist and Professor of Entomology at Penn State. The aphid population consists of stem mothers (individual female aphids) and their recent offspring. The aphids have arrived about two to three weeks earlier than observed in the last three years. This arrival timing is very close to what has been observed in the Midwest over the last few years when they have had significant injury from this pest. Given their early arrival in Pennsylvania soybean fields this year, there is a higher probability that damaging populations may occur in some areas.

Last year, Minnesota treated over 3 million acres of soybeans for this pest. Therefore, it is important that growers and other agriculture professionals be alerted to the presence of aphids in the state. If the population growth of this pest follows past patterns, peak population should be seen in four to five weeks. Based on research conducted at PSU by Wilma Aponte, at 77° F soybean aphids can develop from newborn nymphs to reproducing adults within 5 to 6 days, the large majority of adults are female and each female produces three new nymphs per day for 15 days. Therefore, under optimal conditions, populations can explode very rapidly. Last year, populations increased 10 fold per week.

It should be noted that lady-bird beetles can eat 180 aphids per day and bring them under control within a week of their arrival in the field.

Economic Threshold: 250 aphids per plant - if one or more lady-bird beetles per plant are observed at this time, then it is likely that they will bring the aphid population under control.

Populations seen in the Midwest last year: 0 to 15,000 per plant with ½ of acreage treated
Populations seen in Pennsylvania last year: 0 to 1,500 per plant with less than 1% of acreage sprayed.