KINGMAN - Zinc is classified as a micronutrient, also known as a trace element/trace mineral. Micronutrients are required in very small quantities; in fact, excess amounts can be toxic.
Zinc and manganese are both thought to function as catalysts in the utilization of other nutrients and functions, such as chlorophyll. Chlorophyll is the green plant pigment that absorbs light energy necessary to the process of photosynthesis. Zinc also has a direct relationship to the sweet taste in vegetables, fruits and nuts. Zinc is the second most-common nutrient deficiency in tree crops grown in arid/alkaline soils.
Zinc is taken up by tree roots and absorbed through leaves in an altered form. Like iron, manganese and many other minerals, zinc combines readily with other elements, allowing the plant easy absorption. Zinc deficiency can result from heavy applications of artificial fertilizers. The lack of zinc or a high pH can reduce the mobility of nutrients in the soil and make them unavailable to the plants, causing deficiencies. Symptoms of zinc deficiency may include leaves remaining very small, a decrease in stem length, interveinal chlorosis (yellowing of the leaf, but veins remain green) on young leaves, fewer fruit buds, delayed blooming, smaller crop, and twig die-back after the first year.
Soil with a high content of organic matter will have a sufficient amount of available zinc.Use of compost, organic fertilizer and increased aeration will usually release the zinc that is present but not available from the soil. Be careful when adding zinc. Too much can quickly cause a zinc toxicity. Large amounts of nitrogen, phosphorus and potassium can tie up zinc and make it unavailable to plants.
Identifying your problem as a zinc deficiency can be tricky. Many of the same symptoms can appear and be other types of deficiencies. If you have definitely identified the problem as a zinc deficiency, there are actually two solutions. The best solution is the use of compost, organic fertilizer and increased aeration, but this is also a very slow solution. Organic zinc is available in aged manure, rock phosphate, fish, seaweed and compost. The organisms and fungi which break down organic material in your compost pile also assimilate zinc into a form plants can absorb.
The second solution; foliar sprays and chelated formulations are available to correct the problem. Application timing depends of the fruit or nut tree in question. An early to mid-November application of zinc sulfate is recommended for almond, apple, apricot, cherry, pear and plum. Leaf burn and defoliation may occur as a result of this spray, but it is not detrimental at this time of year. The dormant zinc spray should not be made at the same time as a dormant oil spray. To correct zinc deficiency in peaches and nectarines, apply in April; on walnuts, a spring application is recommended. Follow label instructions explicitly for dilution rates.
During the growing season, chelated zinc sprays can be applied without leaf burn. Do not spray trees or plants during the heat of they day. Very early morning or late evenings are the best time for spray applications.