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 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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