Wheat, used for white bread, pastries, pasta, and pizza, has been the principal cereal crop since the 18th century. It was introduced by the first English colonists and quickly became the main cash crop of farmers who sold it to urban populations and exporters. In colonial times its culture became concentrated in the Middle Colonies, which became known as the "bread colonies". In the mid-18th century, wheat culture spread to the tidewaters of Maryland and Virginia, where George Washington was a prominent grower as he diversified away from tobacco. The crop moved west, with Ohio as the center in 1840 and Illinois in 1860. Illinois replaced its wheat with corn (which was used locally to feed hogs). The invention of mechanical harvesters, drawn first by horses and then tractors, made larger farms much more efficient than small ones. The farmers had to borrow money to buy land and equipment and had to specialize in wheat, which made them highly vulnerable to price fluctuations and gave them an incentive to ask for government help to stabilize or raise prices. Wheat farming depended on significant labor input only during planting, and especially at harvest time. Therefore, successful farmers, especially on the Great Plains, bought up as much land as possible, purchased very expensive mechanical equipment, and depended on migrating hired laborers at harvesting time. The migrant families tended to be social outcasts without local roots and mostly lived near the poverty line, except in the harvesting season. From 1909 to today, North Dakota and Kansas have vied for first place in wheat production, followed by Oklahoma and Montana.