Zinc aids synthesis of plant growth substances and enzyme systems and is essential for promoting certain metabolic reactions. It is necessary for production of chlorophyll and carbohydrates. Symptoms first appear on the younger leaves and other plant parts. Deficiency in corn is called white bud, because new growth turns white or light yellow. Other symptoms include bronzing of rice, rosette of pecans, little leaf of fruit trees, and severe stunting of corn, sorghum, dry beans and soybeans. Zinc becomes less available as soil pH increases. High soil phosphate availability can increase the severity of zinc deficiency. Much of the soil's available zinc is associated with the organic fraction and deficiencies may be associated with low soil organic matter.