David Doll4 CommentsDecember 5, 2021Nutrient

Managing low hull boron: late season corrective measures before next year’s bloom.

Recently, boron hull analysis was provided by an almond farmer. The analysis consisted of two samples from his ~300 acre (~125 ha) third-year farm. The results were 62 and 84 ppm from the cultivars Nonpareil and Monterey, respectively. Both values were under our targeted hull analysis of 95-105 ppm, with the Nonpareil sample also being deficient (<80 ppm). This orchard has followed a boron program since the beginning of its development. Initial soil samples had indicated very low boron (<0.2 ppm, undetectable), high soil pH (7.7-8.2), and a clay loam texture across the operation. Prior to planting, soil sulfur was applied to lower the pH, as well as diammonium phosphate and potassium sulfate. After establishment, boron in the form of disodium octoborate tetrahydrate (20.5% boron, tradename: Solubor®) was applied at 5 lbs/acre (~5.5 kg/ha) twice a year (spring and fall) through the drip system. A foliar application of sodium tetraborate was also made at 1.8 lbs/acre (2 kg/ha) in the fall after the second year of growth and pink bud. As a result, soil boron levels have improved slightly, with some detectable boron within the wetting pattern. Boron deficiency can greatly impact almond yields. Boron improves pollen tube germination and growth, helping to increase the number of flowers fertilized during pollination. Being deficient in boron can lead to very low nut set and yield, and a willowy- look to the trees. More on this can be found in previous articles (here and here are a few). Given that the most recent hull samples indicate deficiency or borderline deficiency in boron, a new plan has been developed. This plan will utilize additional foliar sprays and soil boron applications and will be applied through dormancy and into the next year. The grower has already applied 5 lbs/acre (5.5 kg/ha) and 2 lbs/acre

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David Doll4 CommentsMay 13, 2017Diseases, Horticulture

Almonds Exuding Clear Gum

Several calls about gummy nuts were received this week. Of concern are nuts that are oozing clear gum along the suture or side of the hull. There are many potential causes of clear gumming, which include bug damage, boron deficiency, and internal causes from an expanding kernel. Bug damage. Most people are aware of leaf footed plant bug damage. Feeding by this insect can kill the almond embryo when the insect inserts its needle-like feeding tube into the nut. This often leaves a small pin-prick hole which results in clear gum being exuded 3-10 days after feeding. Although the risk of the bug killing the embryo decreases after shell hardening, there can be some staining of the kernel. As the season progresses, feeding by plant bugs decrease, while stink bug feeding can increase. These insects do not have long enough mouth parts to feed on the kernel, but feed on the fruit instead. They often have several feeding points on a single nut. All of these may gum. Severe feeding by stink bugs may impact kernel quality, but the economic threshold of these insects is unknown. Boron deficiency. Too little boron can cause gumming. Usually a clear gum exudes out of the side of the nut or suture line. When cutting the nut open, the kernel is often discolored with copious amounts of gum. These nuts often drop from the tree, and if not, the gum can harden and misshape the kernels, impacting kernel quality at harvest. Another sign of deficiency is a low crop set. Tree boron status should be determined by hull analysis – which has been discussed previously.  This type of deficiency is common in areas that use clean surface water and have not applied any boron to the soil. Physiological- expanding kernels. Occasionally, almonds can gum for no apparent reason.

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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 Doll2 CommentsSeptember 6, 2016Nutrient

Postharvest is a Good Time for Boron Foliar Sprays

Boron is a critical micronutrient for fruit set.  Work has shown that yield can be reduced when boron hull concentrations fall below 80 ppm. In order to determine deficiency, a hull analysis should be taken to determine tree boron status. Leaf tissue levels are not consistent in providing boron status. Applications of boron should occur to the ground if hull levels are below 80-100 ppm. Boron foliar applications, however, should be considered for nearly all orchards except ones approaching toxicity (hull boron greater than 200 ppm). Boron foliar applications have been shown in several studies to increase yields in orchards deemed boron sufficient. A study from 1999 compared the application of foliar boron at two locations – one in Fresno County and the other in Glenn County – for two years. The Fresno County location applied the foliar sprays either in September, December, or February at three rates (0 lbs/acre, 0.71 lbs/acre, and 1.5 lbs/acre of boron) using Solubor® (a 20.5% boron product). The Glenn County site applied the foliar spray either in August, September, or February at four rates (0 lbs/acre, 0.71 lbs/acre, 1.11 lbs/acre, 1.50 lbs/acre, and 1.91 lbs/acre of boron) using Borosol® (a 10% boron product). At the Fresno Location, the September application was the most effective in increasing tree boron levels, fruit set and yield. All rates out-performed the control. At the Glenn County location, the increasing rates increased tree boron tissue levels almost linearly for the August and February timings. February application timings at both sites increased initial fruit set, but the greatest increase in tissue concentration, nut set, and yield response came from the September timing. The increases observed are most likely is due to the increased efficiency in nutrient uptake from the active leaves. If a September application cannot be made, a February/early pink bud spray should be considered. Ground applied boron should

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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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David Doll5 CommentsJuly 12, 2014Nutrient

Importance of Hull Sampling for Boron

Boron is a micronutrient for almonds. It is required in the process of flower fertilization, being involved in directing the germinating pollen tube. Deficiencies lead to a reduced nut set, and in severe cases, an appearance of a “nonproductive symptom.” Within the tree, boron deficiency can lead to a dieback of small twigs and a “weeping branch” like look.  Boron is also toxic at too high of concentrations.  Often being found in areas with high soil boron or in blocks irrigated with water containing boron, toxicity symptoms appear as gummy nuts that may  form “stick tights” or presence of gum exuding from pruning wounds, bud and leaf scars, and spurs.

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David Doll3 CommentsMarch 24, 2014Irrigation, Salinity

Well Water Analysis to ID Salinity Issues

There will be an increase reliance on groundwater for 2014. Wells that have been typically relied on to subsidize water allocations are now providing the primary source of water for the drought stricken almond orchards. If using a well, it is important to sample the water. Sampling will determine the characteristics of the water such as dissolved salts, pH, and major cations and anions. Sampling should be performed regularly, and more frequently if well performance or pumping depth has changed. 

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