Zinc deficiency is common in peach, plum and nectarine orchards in the San Joaquin Valley. Generally, it is a rootstock problem as typical orchard soils are not deficient, but Nemaguard is a poor forager for this nutrient. Some other rootstocks do not exhibit the same problem. Symptoms include interveinal chlorosis and narrow, pointed leaves that are particularly noticeable in the early spring. Flowering, production and fruit quality can be greatly diminished by this disorder.
Mid summer leaf samples can be useful, but should be compared to other indications of deficiency. A survey of commercial orchards showed most were deficient (< 15 ppm) or marginally low in Zn. However, none of these orchards had leaf symptoms of deficiency. Therefore, a treatment is probably warranted only if symptoms are present and/or leaf samples are extremely low (10 to 12 ppm). Based on trees in sand tanks, we have proposed changing the Zn deficiency threshold to 10 ppm (Refining Deficiency Levels). Also, we have experimented with a dormant sampling protocol that shows promise of identifying truly deficient orchards.
Using Nemaguard seedlings in the greenhouse, we have compared the efficiency of many different formulations (see FREP Final Report 2008 - 2010). We concluded that correction of Zn deficiency can be achieved most efficiently with foliar applications of zinc sulfate (36% Zn) in the early fall (see Testing the Timing of Zinc Applications). Other formulations can supply Zn to the tree but are generally less efficient and more expensive. If spring applications are needed, formulations showing less phytotoxicity would be advisable. For newly planted trees, we have developed a procedure for adding zinc to the planting hole (Adding Zinc to Planting Holes).
Slideshow of Zinc Deficiency Symptoms
Nutrition Chapter in UC Stone Fruit Manual