The proliferation of synthetic fertilizers, pesticides, herbicides, and fungicides in the 1950s, has subsequently led to the degradation of the soil. Such chemicals act as salts, killing off the necessary microbiotic life forms that support healthy soils. Sustainable farming is a reaction to the use of such chemicals, regarded as a pragmatic approach, where chemical treatments are used only when absolutely necessary. Biodiversity in the vineyards is encouraged through the planting of cover crops, rigorous plowing of the soils, and the use of manures and natural composts to fertilize the vines. Some growers use this as a first step towards full organic farming. Others find it a happy medium between conventional methods and the stricter demands dictated by organic certifying agencies. There is a wide berth of interpretation concerning these methods. Some farmers work through certifying agencies such as Terra Vitis, following a specific set of specifications and requirements. Others farm independently, following organic methodologies, and reserving treatments only when conditions are optimal (for example, when there is no wind). Zoologists have introduced more environmentally-friendly concepts such as integrated pest management, or hormone confusion, which prevents the reproduction of certain pests that may threaten the vines. The reduction of sprays not only contributes to the health of the vines and the greater ecosystem, but also to the health of the winegrowers (who account for the largest percentage of cancer cases among farmers).