Pesticide residues on plants degrade to harmless byproducts over time. Toxicity varies among pesticide products, however, as does the amount of time necessary for degradation. The toxicity of pesticide residues has been tested and, in some cases, restrictions have been placed on the use of a product. The restrictions are usually labeled "Days-to-Harvest Intervals" (DHIs) or "Preharvest Interval" (PHI). The DHI or PHI is a period of time that must pass before fruit can be harvested after the application of a particular pesticide. If DHIs or PHIs have been established, they can be found on the pesticide label.