Zinc is one of the most important nutrients for fruit trees. It is critical for the formation and function of chlorophyll, several enzymes, and the growth hormone auxin. Auxin is key to apical dominance – the phenomena that we are controlling when we prune and train trees.
Zinc deficiency symptoms are most obvious in the Spring on shoots that grew last year. The deficiency appears as small, narrow leaves (little leaf), blind wood in the middle portion of vertical shoots (little or no bud growth) and a group of normal leaves that look like a palm tree at the top. If the deficiency is severe branches will die. In most cases trees grow out of these symptoms as weather warms up, so take note and plan to apply zinc this fall or winter.
Zinc deficiency is most often seen in apples, cherries, and pears.
Zinc levels in fruit trees can be very low even if soil samples indicate high amounts as the zinc in soils is often not available to the trees. Zinc does not move readily within the plant due to translocation problems. This situation is why all commercial orchardists apply Zinc as a foliar spray. The most common form used in commercial orchards in British Columbia is Zinc Sulphate applied to Stone Fruits in late dormant and Apples and Pears at silver tip. For bud stage definitions see Bud Stages.
Some fertilizer suppliers sell Zinc Sulphate in small amount for home orchardists. If you find a good supplier or are unable to find any, contact me for assistance.
For lots more details see Washington State University Zinc or BC Tree Fruit Nutrition.