Franz Niederholzer4 CommentsOctober 11, 2016Nutrient

Fall Foliar Nutrients – Zinc and Boron Review

Symptoms of zinc deficiency of almond Written by Franz Niederholzer, UCCE Advisor, Colusa and Sutter/Yuba Counties Bloom is the most important time of the year for adequate boron (B) and zinc (Zn) levels in almonds.  Zinc is essential to many processes such as cell division, protein synthesis and auxin synthesis in growing points (flowers and shoots), and bloom is the time of the most growing points in a tree.  Boron is essential for cell wall synthesis and division. Boron fertilization has improved fruit or nut set compared to deficient plants in many crops, but only if applied in time to get B into buds at bloom.  Both Zn and B can be absorbed into leaves and translocated within almond trees. Check leaf symptoms, summer leaf analysis or hull analysis results to see if Zn and/or B fertilization is needed.  Zinc deficiency produces “little leaf” symptoms (see photo below), with trees showing summer leaf levels of 15 ppm Zn or less considered deficient.  Trees with hull B levels below 80 ppm B at harvest are thought to be deficient, but almond yield may benefit from B application if hull levels are below 120 ppm B.  Do not fertilizer with B if hull levels are 200 ppm B or greater, as excessive B is toxic to plants. A fall foliar nutrient spray is a cost effective way to get Zn or B into buds for the following year’s bloom.  The return on investment for a fall B spray can be significant.  Yield increases of 200-400 kernel pounds per acre have been measured from a foliar nutrient application the previous fall at Nickels Soil Lab of 0.6 lbs. of actual B (the equivalent of 3 lbs. Solubor®/acre applied in 400 gallons/acre). Fall Zn sprays should increase leaf Zn the following year and eliminate Zn
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David Doll0 commentsSeptember 14, 2016Diseases

Defoliating for Rust Management…Good Idea?

Written by David Doll (UCCE Merced County) and Brent Holtz (UCCE San Joaquin County) The foliar disease rust caused by the fungus Tranzschelia discolor has been a major problem this year. This disease is characterized by rusty-brown- or black-colored spores that form on the lower side and angular chlorotic (yellow) lesions on the upper side of the leaf. Rust can spread easily from orchard to orchard with wind, and minimal periods of leaf wetness are required for the pathogen to infect. This past year, long periods of conducive conditions, which include warmer temperatures, late spring rains, and increased canopy humidity were experienced, making rust management a challenge. Rust is easily controlled by properly timed fungicides. Several modes of action provide protection. Those with the highest activity are FRAC Groups 3, 11, and 19 or mixtures of these groups. Also several broad-spectrum fungicides such as micronized sulfur (M2, microthiol) and chlorothalonil (M5, Bravo) have very good efficacy with short- and long-residual activity, respectively. Since rust can infect from spring to summer, sprays need to be timed accordingly. Spring sprays (2-5 weeks after petal fall) based on monitoring for rust symptoms is often used to initiate rust control practices at the beginning of a potential epidemic. One fungicide application, however, may not provide effective control if favorable conditions persist and later sprays may be needed. Typically, spring-time disease management programs for scab and Alternaria leaf spot will also provide management for rust. High populations of rust can prematurely defoliate trees. As the fungus spreads, it ruptures leaf tissues, reducing the photosynthetic potential of the leaf, and eventually causes leaves to fall. If too many leaves fall from the tree, the tree will re-leaf, reducing the cropping potential for next year. Although this re-leafing is concerning, it is better for the tree to re-leaf

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Allan Fulton0 commentsNovember 6, 2015Soil

Understanding and Applying Information from a Soil Test, Part 4: Boron, Chloride, Copper, Iron, Manganese, Molybdenum, Nickel, and Zinc

Allan Fulton, UC Farm Advisor, Tehama County and Roland D. Meyer, Extension Soil Specialist Emeritus This article (Part 4) discusses micronutrients and the use of soil tests to evaluate their levels in orchard soils.  Micronutrients are essential to almonds and other nut crops, yet are required in much smaller amounts than macronutrients such as nitrogen (N), phosphorus (P) and potassium (K) or secondary nutrients  such as calcium (Ca), magnesium (Mg), or sulfur (S).  The eight micronutrients are boron (B), chloride (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn).  They fulfill important roles in the plant.  For instance, zinc is needed for plant cell expansion and it influences pollen development, flower bud differentiation, and fruit set while boron is a building block for the plant cell wall and strongly influences pollen tube germination and growth.  Flower abortion in almond and walnut has occasionally been associated with boron deficiency.  Nickel has recently been determined to be an essential nutrient and there are no known deficiencies in California. Zinc, iron and manganese deficiencies are not as commonly found in the Sacramento Valley as in the San Joaquin Valley.  Zinc deficiency is most common in almond and other nut crops.  Other micronutrient deficiencies that are occasionally seen in almond include B, Fe, and Mn.  Copper (Cu), Mo, and Ni deficiencies have not been documented in almonds; however, Cu deficiency is common in pistachios. Five of the micronutrients (Cu, Fe, Mn, Ni, and Zn) largely exist in the soil as positively charged metal cations bound as minerals or adsorbed to the surfaces of colloids or soil particles.  Several factors in orchard soils may affect the solubility and availability of these metal cations to trees.  Soil pH greater than 7.5 has the major influence of reducing the tree availability of

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