In the Texas Pecan Handbook, John Begnaud, Extension Horticulturalist writes that, “Over 40 years of pecan zinc research confirms that the pecan tree is a poor accumulator and transporter of zinc, especially when grown in high pH soils.” Any commercial pecan grower in the state can testify that this statement is true and none of them will miss a zinc spray unless it rains. Unfortunately many new growers and perhaps some in the business a long time forget how important zinc is in pecan growth.
What does zinc do? Well zinc is necessary for the production of natural plant hormones that induce cell elongation and cell division or better said overall plant growth. In our high pH soils we can have lots of zinc but little of it is available to the tree and so we see deficiency symptoms such as small, narrow leaves. These leaves are usually on thin shoots with very short internodes. When you only have small leaves and possibly less leaves then you don’t produce pecans or a smaller crop than expected. Continual zinc deficiencies can result in bunchy terminal growth and even some canopy die-back. Dr. George Ray McEachern, pecan specialist, describes zinc deficiencies as small leaves that curve, leaf edges waxy, leaves with dark interveinal discoloration, shoots growing in thick bunches with some dead some alive.
Now what do we mean by zinc applications? In the many research trials that have been done the only effective and efficient way to get zinc into a pecan tree is foliar applications. Over the years soil injections, tree injections and fertilizer applications have all been tried but still foliar applications are the best. Unfortunately our high pH soils very quickly make and soil applications of zinc bound up and unavailable. Tree injections move zinc to existing growth but since zinc is immobile in the plant the new growth doesn’t get the benefit. This unique set of circumstances forces growers to make repeated foliar applications to new growth to ensure adequate zinc uptake in pecan leaves.
Another aspect of the zinc research in pecans is the best formulations for zinc uptake. To date three compounds have been the most effective, zinc sulphate, zinc nitrate and NZN. Of these three the most widely used is zinc sulphate probably because it is just as effective as the other two but is cheaper. Another part of this research has shown that the effectiveness of zinc uptake is enhanced by the addition of liquid nitrogen in the tank. It doesn’t take much zinc or liquid nitrogen, only 2 lbs of zinc sulphate and 1 quart of liquid N per 100 gallons of water. For homeowners there are numerous products on nursery shelves for zinc applications and all work well. Use a hose-end sprayer to reach tree tops.
Now the hard part is getting the trees sprayed on a timely basis. Remember that zinc is not translocated so a grower needs to make regular sprays during the spring flush. The first spray should be at green tip or what we call budbreak, then 1-2 weeks later followed by another 1-2 weeks later or with casebearer insect sprays and then one more 2-3 weeks later. Pecan growth is fairly mature by mid-June so that sprays can be discontinued on all but young trees which should be sprayed until August.
Of all the things you can do to a pecan tree to help make pecans there is probably nothing more important than zinc sprays and now is the time to get started!
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- Bob Whitney
- As an Agriculture Extension Agent for Texas AgriLife Extension Service I have had an opportunity to be involved in just about every aspect of agriculture. From the 5,000 cow dairy to the types of trees to use in a home landscape I have had a chance to learn how the different parts of an agriculture systems work together. Seedless watermelons, drip irrigation, pecan orchard management, fruit crop development, dairy nutrient management, environmental issues confronting agriculture, producer tours, field days, research projects and more have been a part of my life for over 30 years as I lived and breathed agriculture. Since 2004 I have been actively involved in consulting internationally working in Honduras, Guatemala, Egypt, Jordan, Iraq, India, and China. I have worked with missionaries and other groups dedicated to alleviating poverty among third world farmers. I lived in the Middle East in 2007-2008 working on a project for the Borlaug Institute of International Agriculture at Texas A&M University. In this project I was the Chief of Party and Team Leader for a $5.7 Million dollar effort to train Iraqi Extension agents and specialists in all aspects of agriculture.