Nutrient Management Research Database

Zinc (Zn) deficiency is commonly observed in California peach trees, particularly when grown on Nemaguard rootstock. Foliar sprays are generally applied yearly to alleviate the problem or, in many cases, to prevent the problem from occurring. Some of these applications are probably unnecessary. In addition, zinc is not taken up very efficiently into plants, so relatively high rates of different formulations are applied in order to supply a small amount to the trees. One of the objectives of our research has been to improve both the sampling and application procedures for zinc with the goal of eliminating unneeded sprays and/or reducing the amount of material applied. A more thorough understanding of the movement and distribution of zinc within a peach tree should provide clues and suggest strategies for achieving this goal.

This source covers the following topics:

• Zinc Distribution within a Peach Tree 
• Implications for Nutrient Sampling
• Implications for Zinc Treatments

Zinc Distribution within a Peach Tree 

• Zinc distribution varies throughout a single tree.
• Higher zinc concentrations are present in the lower canopy. 
• Shoots on the inside canopy have higher concentrations than those on the outside of canopy that are exposed to more sunlight. Inner shoots can have as much as 5 times higher zinc concentration. This likely reflects the transfer of zinc from the shoots into the roots for storage.
• Deficient trees have more zinc near the shoot tips, while the opposite is true for trees high in zinc. Trees with normal zinc levels don't show these differences.
• These factors contribute to a newly proposed sampling procedure, where fruiting shoots are sampled during the dormant season.

Implications for Nutrient Sampling

• While distinguishing between trees with high zinc and those that are deficient is relatively simple. However, distinguishing between typical, acceptable levels and those are are deficient presents more challenges.
• As the season progresses, leaf samples do not capture the different nutrient statuses as accurately.
• Early spring leaf sampling is therefore the best approach to identify deficient trees.
• Summer or fall foliar applications make this sampling timing not work as well.

Implications for Zinc Treatments

• The slow, consistent transfer of zinc from shoots to roots suggests that periodic applications of a small amount of zinc throughout the season can be effective. However, this approach would be quite expensive.
• Field trials with varying rates and timings are need to identify the most effective way to fertilize peach trees with zinc.