However, cross-pollination rates vary considerably in recent studies as well. In USA, Jemison and Vayda (2001) used a herbicide resistant maize field exposed upwind of predominant wind directions to the recipient field. In 1999, there was no cross-pollination at a distance of 350 m, but in 2000 cross-pollination between 0.7 and 1.4% took place at a distance of 100 m in a field with asynchronous pollen production. In a region characterized by low humidity and frequent high winds (Colorado, USA), using blue grain colour and herbicide marker hybrids as the pollen donor, cross-pollinations of 0.3% at a distance of 80 m and of 0.05% at a distance of 180 m were detected in organically cultivated maize (Byrne and Fromherz, 2003).