Mobility within tree: Low/Fair

Uptake Form: Zn²⁺

Function:  protein breakdown, enzyme activation

Deficiency/Toxicity Symptoms:  Zinc deficiencies are common in tree fruits in Okanagan region. Zinc is required for protein breakdown and in enzyme activation in plants (Maher 2004). Zinc deficiency is first recognized by interveinal leaf chlorosis similar to Mn deficiency.  New leaves are smaller than normal and there is reduced shoot elongation causing leaves to be closer together.  Terms such as “little leaf”, “rosette”, “yellow” and “bronzing” are used for Zn deficiency.  In stone fruits, small yields of small misshapen fruit are produced.  Zinc toxicity usually results in Fe chlorosis. Zinc deficiencies do occur in soils where the topsoil or organic matter has been removed (Maher 2004).

Zinc (Zn) Sources and Application

It is common for leaf Zn concentrations to remain low, even after application of recommended dormant Zn sprays.  Zinc deficiency symptoms such as chlorosis, blind bud, rosetting and little leaf can, however, be reduced by such applications.  Zinc does not easily wash off leaves and the use of chelated Zn products or Ziram in the spring/summer will contaminate leaf sampling for subsequent nutrient analysis.  Use early dormant spray timing if plans are for doing leaf analysis in the summer to monitor Zn levels. 

For apples, it is recommended that Zn sulphate be applied annually at silver tip to green tip stage of bud development (stages 2 and 3), supplemented by one or more sprays of chelated foliar formulations of Zn during the growing season.  It is not recommended to use chelated products, such as Zintrac, mixed in with the dormant oil sprays as a replacement to Zn sulphate applications.  Chelated products are designed for best absorption when applied directly to leaves. 

Two zinc sulphate sprays are recommended for cherries; the first during the late dormant period up to bud swell stage (stage 2).  Do not mix with the dormant oil spray.  The second spray can be applied within 2 weeks after harvest.  Chelated zinc products can also be used during the growing season to help supplement Zn, but should never fully replace the dormant zinc sulphate spray. The common sources and application rates for Zn in fruit trees are summarized in Table 1. 

For pears, an annual application of zinc sulphate is usually adequate.  Apply at green tip stage (stage 3) before dormant oil.  For other kinds of fruit trees showing low Zn levels, a zinc sulphate application at late dormant stage should be applied annually.

Table 1. Possible zinc foliar application rates for fruit trees

^a May be applied with sprays of boron, manganese, magnesium or urea.

^b WARNING – Do not apply at air temperatures above 30°C, do not mix with other chemicals and do not allow drift to other crops.