Farmers advanced through oxen, horses and mules, steam tractors and then tractors with internal combustion engines to provide power on farms. Tractors started to be a competitive source of power in the early 20th century as progress moved from steam to internal combustion engines and steel to rubber tires. Early reapers and binders were forerunners of stationary threshing machines and mobile combines or mechanical harvesters for grain, beans and cotton, which became available over 1930-1960s. However, mechanical harvesting of fruits and vegetables generally lagged behind. The invention and later adoption of the self-propelled processed tomato harvester in the mid-60s was a major labor-saving factor for that industry; later related inventions yielded further labor-saving and product quality improvements. Mechanical harvesters have been developed for some other fruit and vegetables, although much of the industry still relies on hand harvesting. Even without mechanical harvesting, labor aids, which improve labor productivity instead of replacing labor, have made the harvesting process faster and with less stress on workers’ backs. Calvin and Martin (2010) report an estimate from 2000 that 75% of vegetables and melons are harvested by machine and 55% of fruit production, with processing products being more likely mechanically harvested than fresh.