Northwest Iowa Extension Crop and Pest Information by Todd Vagts ISU Extension Crops Specialist Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.
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2004 Aphid Population Detection and Growth Parameters for N.W. Iowa

Southeast MN as the source...view Minnesota Department of Ag Pest Survey
As of August 02 only 16 fields have been identified with (very low) aphids.   Compare to the same period in 2003 when aphids were found in all fields.

Wind Direction (transporting aphids to N.W. Iowa)
-No aphids yet to transport from other areas

Local Mean Temperature (Optimum 72 - 77 degrees F.)
-Aphid populations are much easier to find now in IA, MN and eastern NE.  Aphid population growth has been relatively slow so far.  The optimum temperature for aphid population growth is 72 to 78 degrees (more on aphid population growth).  The following graph shows the average temperature as recorded at four weather stations in N.W. IA, compared to the average temperature recorded in 2003.  Actual data is current to August 29, then forecasted data for 2004 was used to September 5. 

See the following pdf document for detailed comparisons of 2001, 2002, 2003 and 2004 average temperatures for N.W Iowa (north or south of Hwy 3).  Temperature Comparisons

Local Average Relative Humidity (Optimum < 78%)
-Aphid populations tend to increase better under low (<78%) humidity conditions.  The following graph shows the average relative humidity levels as reported at four N.W. Iowa weather stations comparing 2004 (current to August 29) to 2003. .

See the following pdf document for detailed comparisons of 2001, 2002, 2003 and 2004 average Humidity for N.W Iowa (north or south of Hwy 3).  Humidity Comparisons