The soil in Florida is generally low in fertility, and the climate conducive to plant diseases and insects. In peninsular Florida as much as one ton of fertilizer is needed annually for each acre. Large quantities of herbicides and pesticides are also applied. Labor costs are higher than in many other parts of the nation, because many Florida crops cannot be mechanically harvested. Contract laborers, usually migrants from the Caribbean basin, harvest vegetables, fruit, and sugarcane as well as care for nursery plants. Elsewhere sugarcane is mainly harvested by machines, but Florida's sugarcane is grown on soft, organic soils on which the machines operate poorly. Irrigation is as important to Florida farmers, particularly in the southern part of the state, as it is to those of California and Arizona.