Pollination timing varies from field to field, depending on planting date, maturity of the hybrid and the weather. Pollination typically lasts only from five to ten days. Fields next to each other may pollinate at different times. How pollen travels depends on environmental factors, such as the wind, temperature and humidity. These, of course, vary from season to season, from area to area.
Distance minimizes pollen contact.
The farther apart fields are, the less likely their pollen can mix. In addition to natural pollen mixing, mechanical mixing is a possibility. For instance, if growers does not clean out their combine between fields, there is a possibility grain can be mixed. If pollen mixing does occur, it's likely to be minimal. However, it can be detected, depending on the testing procedures and policies of the local grain handler.