An estimated 100 million African women spend over 20 billion hours of hard, manual labour to chop weeds from crop fields (Deltafarmpress.com; accessed November 21, 2013). The manual weed control efforts do not eradicate all weeds. According to Leoanard Gianessi of CropLife Foundation; despite spending 200 hours per hectare to remove weeds; farmers still lose 20 – 100 percent of potential yield to weeds.