Pecan Zinc Management: Science & Misconceptions

Monte Nesbitt Leo Lombardini Extension Horticulture Horticultural Sciences College Station, Texas Texas A&M University Zinc

wikipedia

* 24th most abundant element in Earth’s crust * 8th metal known to man. * Component of ancient brass artifacts. * Human bodies contain only 2-3 grams * cancer prevention, immune system boosting, sleep regulation, and preventing Alzheimer’s disease, anxiety and depression. * Pecan kernels contains 9% DV per ounce Role in plants

* Discovered in 1926 to be essential (minor/ micro) plant nutrient. * Linked to rosette symptoms on pecan by researchers in 1932 &33.

Chesters & Rollinson, 1950

Mild to moderate symptoms Severe symptoms Small leaves, lateral bud breaking, dwarfy-appearing trees. Highly calcareous soils in the west region have worst problem In Texas, Dr. J. Benton Storey led research efforts on pecan zinc nutrition, developing foliar products like NZN and establishing rates effective for growing pecans successfully in the far west region. Essential means ‘must have’

• Needed for synthesis of amino acid Tryptophan. • Regulation and consumption of sugars • Formation of starch and proper root development. • Synthesis of chlorophyll and carbohydrates. • Withstand lower air temperatures. • Improved cell integrity and disease resistance

Zn Tryptophan IAA Cell growth & expansion Misconception : Zn is only needed for foliage development

Pecan research studies have shown Zn deficiency causes:

* Negative impacts on photosynthesis * Shorter catkins * Delayed pollen shedding Some effects require severe * Reduced flower set deficiency * More fruit death * Smaller nut size * Erratic shuck opening. Misconception: Pecans do not take up zinc through their roots.

* Pecans with good mycorrhizal root associations in undisturbed, organic and low calcium carbonate soils can take up Zn. * Zn is deficient in most North American soils. * broadcast to the soil surface may take years to get to the roots. * Quickly reacts and binds with carbonates=insoluble For most growers in Texas, one or more of these obstacles prevent soil/root Zn uptake Storey found it took 278 lbs Zn/tree to get to minimum leaf levels in west Texas. Is soil banding an option?

* Wood (2007) in Georgia demonstrated maintenance of leaf Zn levels above the 50 ppm sufficiency level for four consecutive years by placing a 4” x 12’ band of zinc sulfate or over two drip irrigation lines positioned on either side of the tree row. www.noble.org * Calcitic soils in Texas likely present a greater obstacle. What about soil-applied zinc chelates?

* Walworth & Heerema (2015) applied Zinc EDTA through microsprinkler irrigation system (multiple applications/year) for four years in Arizona with soil pH of 8.1 * 2 lbs/Acre, 4 lbs/Acre, untreated check * Increased DTPA-extractable soil zinc in sprinkler wetted area * In Wichita, visual deficiency symptoms decreased significantly at both rates ; leaf Zn levels increased significantly in the 4 lb treatment, and trunk diameter and yield increased in the last two years at both rates. * Nut yield and trunk diameter not significantly different in Western trees * Maximum Wichita leaf zinc levels of 22, 25, 24 and 37 ppm (years 1-4) * No foliar treatment check in the study to compare.

Science: Foliar spraying is effective approach for annual Zn fertilization in calcareous soils.

On mature, bearing trees, foliar sprays in early Spring are effective. Zinc Timing Chart

4

Fourth—Casebearer time

Third—4 weeks after

Second-1 or 2 weeks after Fifth—12 weeks after

Photo Collection: J. Benton Storey On young trees, sprays made anytime to new flush growth are helpful. *Bi-weekly, April to August

Texas A&M Orchard, Brazos River Bottom, photo:McEachern Misconception: Any product with Zn in it can do some good as a foliar spray.

* Zinc Sulfate wettable powder has been proven effective. * Zinc liquid (ZnNO3) 17% has been proven effective. * Zinc Oxide has been proven effective. * Zinc chelates (foliar) have variable track record. Foliar Rates

* Zinc Sulfate: Mature trees--2 lbs per 100 gallons of water/Acre to target 10 lbs of 36% zinc sulfate /acre each season (3-6 lbs/year in Southeast) * Young trees: 1 lb/100 gallons + 2 pts Uan (32% N) * Can burn some other plants (peaches, other) * Zinc Nitrate (17%): 1 Pt -1 Qt per 100 gallons of water. * Far West Texas needs the higher rate * Less phytotoxic to peaches, other plants * Zinc Oxide: 1.4 lbs/Acre * Less effective product choice in some trials. * Equally effective in some trials. * Price may be +/- Example of Grower Product Confusion

7% Zinc Derived from Zinc Nitrate and Urea

Label rate for fruit trees is 1-2 qt/Acre per application 3 times

Grower applied at 1 qt/500 gallons More confusion—not all “zinc ” are equal

5% zinc, no disclosure of source material Label Rate: 0.5-1 qt/ acre in 100 gal solution Derived from zinc sulfate (6.5%)

Label recommends 1-4 qts per acre in a minimum of 15 gallons.

Requires 11 quarts per acre to equal 2 pounds of 36% zinc sulfate Misconception: Nitrogen must be mixed with Zn to get it in the foliage

* Zinc sulfate or Zinc nitrate alone will be absorbed by pecan leaves. * BUT! * 32% Urea (UAN) added at 2-3 pts per 100 gal of water can increase the Zn absorption rate or lower the amount of Zn product needed to get equivalent uptake.

Treatment Leaf Zn ppm Leaflet size Yield (lbs/A) Control 23 20 103 ZnSO4 alone 84 30 442 ZnSO4 + uan 195 31 589 Misconception: Zn sprays are not needed each year, because it will build up in the tree.

* True in the Southeast, if soil applications are also made and liming does not happen. * Not a function of foliar spraying * False in Texas. Foliar-applied zinc is not mobile, and therefore not stored in the tree. * Run-off from foliar sprays will be tied up in the upper soil profile

Science: July Leaf Samples are important to assessing Zn spray practices * Be consistent in sampling month, sample trees, keeping varieties separate, sampling from nut- bearing or non nut-bearing terminals, sun exposed, canopy position, mid-point of growth…

Collect Leaves in July to Assess All Nutrients

Element Dry Wt. Concentration Texas N-Nitrogen 2.5 to 4.0% 50-60 ppm used in P-Phosphorus 0.15 to 0.30 some states (Smith, et K-Potassium 0.75 to 1.25 al, 2012 Calcium 0.70 to 3.00 Mg-Magnesium 0.30 to 0.60 Fe-Iron 50 to 300 ppm Lower threshold used Mn-Manganese 40 to 300 (40 ppm) where Zn is Zn-Zinc 80 to 500 soil applied (Wood, B-Boron 20 to 45 2007). Cu-Copper 10 to 30 Misconception: Pecan leaves collected for Zn assessment don’t have to be washed

* TAMU STUDY_Lombardini (2013): Leaves sprayed with ZnSO4 and not washed before analysis had up to 33X times higher Zn concentration than untreated leaves. * Three types of wash (Distilled water, dreft laundry detergent, and 1% HCl) were effective in removing between 64% and 79% of the applied Zn. Only HCl, however, reduced Zn concentration to levels similar to those measured in untreated leaves. * Grower washing practices need to incorporate an acid wash to improve understanding of true leaf Zn levels. Leaf Washing Procedures

* 1. Send leaves directly to laboratory and request acid wash. OR * 2. Wash leaflets in a 1-percent hydrochloric acid solution (Although it depends on the concentration of the muriatic acid, usually 2 TBSP /gallon of water will approximate a 1% hydrochloric acid solution.), * Rinse in five separate distilled water baths and air dry before shipping.”

http://soiltesting.tamu.edu/ Recommendation Summary

* Sprayer calibration and good coverage is essential to effective uptake. * Use a product that is truly 36 % Zinc Sulfate wettable powder or 17% Zinc Nitrate (harder & harder to find). * Avoid pre-packaged products of zinc and nitrogen that do not deliver proper rates or are uneccessarily expensive. * Time sprays early in the season, and follow up in July with good sampling and leaf washing practices. Questions or Copy of presentation

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