Integrated Crop Management

Aphid numbers up, but less than during 2003

Brian Lang, extension field specialist, Decorah, has been collecting weekly data on soybean aphids from northeastern Iowa during the past four years. The two tables show the percent of soybean plants with aphids and the average number of aphids per plant. Both of these categories show an aphid population that is slightly larger and occurring on more plants than at this same time last year. However, the population does appear to be much smaller than the outbreak population that we experienced during 2003.

Brian also has seen some soybeans with about 1,000 aphids per plant collected near Fort Atkinson, Winneshiek County. The co-op agronomist who found the infestation reported that only part of the field had significant activity, and the population was estimated to average 400 aphids per plant. Field conditions were very dry in this part of the state, which adds to the concern of early season soybean stress and a good environment for aphid buildup.

Percent of soybean plants with soybean aphids, Decorah, Iowa.

Date 2002 2003 2004 2005
June 1 -- -- 0 6
June 7 -- -- 0 15
June 15 -- 40 0 33
June 22 7 90 0 31
June 29 15 100 0
July 6 70 100 4
July 13 93 100 8

Average number of soybean aphids per plant, Decorah, Iowa.

Date 2002 2003 2004 2005
June 1 -- -- 0 0.1
June 7 -- -- 0 1.4
June 15 -- 10 0 2.5
June 22 1 115 0 4.0
June 29 2 341 0
July 6 14 745 0.5
July 13 25 2,803 1

This article originally appeared on pages 130-131 of the IC-494(16) -- June 27, 2005 issue.


Source URL:
http://www.ipm.iastate.edu/ipm/icm//ipm/icm/2005/6-27/aphids.html