Green peach aphid, Myzus persicae (Sulzer), is the primary vector of Potato leafroll virus (PLRV).  In the Red River Valley of Minnesota and North Dakota, introduction of PLRV into virus-free seed potato fields occurs with mid-summer alate dispersal of viruliferous green peach aphid (GPA).  Initial colonization of potato fields by alate GPA is concentrated on field edges at the interface of the crop with fallow, planting skips, drowned out areas, but especially headlands.  In large acreage fields (n=3, 2000-2002), GPA densities (measured twice weekly for two months following colonization) were concentrated within 18 m of the field edge.  Colonization behavior of GPA alatae and within field dispersal rates of 1.8 m per day by apterae provides a spatio-temporal window for targeted pest management.  In 2003, large-scale on farm experiments were conducted using 25 seed fields, each > 8 hectares, to evaluate effectiveness of targeted spray applications for aphid control.  When aphid flight activity spiked (~July 30) an 18 m wide spray swath of methamidophos insecticide was aerially applied to field edges abutting headlands.  Pretreatment green peach aphid densities were 10 times higher on field edges than mid-field.  Methamidophos provided excellent control of early colonizing aphids and 72 h post-treatment aphid densities mid-field did not differ from densities in spray swaths.  Overall, 38.5 of 730 hectares were treated saving an estimated 92.6% ($58.44 per hectare, application costs included) compared to treating the entire field.