"Because the pickers were squatting or kneeling under the vines and twisting to reach up for the grapes (the low-hanging fruit proving the trickiest), their necks and shoulders were soon in agony. Standing up to relieve their backs thrust their heads into the vines, which are covered in pesticides. There are many cases of birth defects and cancer in the families of farmworkers. But as the heat climbed above 100°F (about 40°C), the vines, soaked in toxins or not, became allies. The air underneath them is stagnant, as in a sauna, but their foliage is the only available shade."

The Economist, Field of Tears. 

http://www.economist.com/node/17722932