David Doll2 CommentsJanuary 27, 2011Horticulture, Nutrient

Bloom Spray Additives: Do they work?

Bloom is approaching. Several questions about whether or not bloom spray additives increase flower pollination and set have been asked. I will try and answer them the best I can using information from previous trials across the state. Much of this information is gleaned from Roger Duncan’s presentation delivered at the 2010 Stanislaus Almond Day. Should I include foliar nutrients in the bloom spray?Several trials from four different advisors from areas across the state (Duncan – Stanislaus, Holtz-Madera, and Edstrom – Colusa, and Viveros – Kern) have indicated that nutrients and other additives included with bloom sprays do not increase yield of almonds in properly maintained orchards. In most trials, yields of the untreated control were higher than the foliar nutrient applied treatment. These were multiple replicated trials held over several years. Materials used can be seen by viewing the presentation linked below. This trial data can be seen in Roger Duncan’s 2010 NSJV Almond Day presentation (click link). What about Pristine® Fungicide?Pristine® fungicides is a boscalid/strobilurin mixture that has been used successfully for several foliar fungi that commonly affect almond flowers and leaves (i.e. Brown Rot, Rust, Scab, etc.). There is evidence that suggests that Pristine® causes a yield bump when applied during the bloom or post bloom period. Research by Jim Adascaveg (UC Riverside) and Roger Duncan (UCCE Stanislaus) tested this hypothesis and have not found a significant increase in yield from a bloom or post bloom Pristine® application. It is important to state that in Duncan’s trials (Stanislaus Co.), the yields were higher in treatments containing Pristine®, although not statistically significant. Duncan found this same insignificant yield bump when applying Gem®, another strobilurin, in the post-petal fall period. Conversations with a local consultant indicated mixed success of the Pristine® yield bump across his multi-year trial. Although he

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Joe Connell7 CommentsNovember 1, 2010Nutrient

Late Fall, A Time for Potassium Soil Applications

Maintaining adequate potassium (K) nutrition is especially critical for almond trees and fall is an excellent time to address K deficiency through soil potassium applications.    Potassium is found in one of three forms in the soil:  fixed K, exchangeable K, and K in solution.  Fixed K is tightly held within soil particles or is part of potassium-bearing minerals and may only be very slowly released through weathering.  Exchangeable K is attached by electrostatic charges to soil particles and is in flux with potassium ions in the soil solution.  Soluble K consists of ions moving freely within the soil solution constituting a readily available form of K.  At any given time, a soil will contain a unique balance of fixed, exchangeable, and soluble potassium characteristic of that soil type. Potassium is thus in equilibrium and moves back and forth between these states as the supply of K+ and other cations varies. Potassium ions (K+) have a one plus charge and are readily adsorbed by negatively charged soil clay particles becoming unavailable to the tree.  Avoid any type of application that broadcasts potassium over a large soil area because more of the K becomes fixed. UC research showed that four years of broadcast applications only moved K 6 inches down into the soil while banded treatments penetrated 2 feet.  Banded treatments have worked well under non-tillage but if you cultivate, shank the band in to get the material closer to the root zone.  Applying a gypsum (calcium sulfate) band overtop of previous potassium bands can help free up more potassium.  The calcium ions (Ca ++) in gypsum have a plus two charge and will displace potassium ions on the clay particles thus freeing up more potassium to remain in the soil solution while moving it deeper into the root zone.  Gypsum

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Roger Duncan2 CommentsAugust 2, 2010Nutrient

Hull Samples for Boron Analysis

What is the most common nutrient deficiency in Northern San Joaquin Valley almonds? If you said nitrogen or zinc you are wrong. While zinc and nitrogen are commonly applied to area orchards, boron is often neglected and therefore boron deficiency is far more common. If you haven’t applied boron TO THE GROUND recently and your orchard is east of the San Joaquin River, you are almost certainly deficient. Boron is essential for pollen tube growth. There are no obvious foliar symptoms of moderate boron deficiency, but less than optimum boron can reduce nut set. Analysis of mature almond hulls is a much better indicator of boron status than a leaf analysis. Wait until harvest to collect hulls because they will continue to accumulate boron while splitting. Trees with hull boron levels of less than 120 ppm may benefit from a postharvest boron spray (1-2 lb of a 21% B product in 100 gallons of water per acre). This will help with pollen germ tube growth in the flowers next spring but will not improve overall boron status of the tree. Hull boron of less than 80 ppm indicates the need for a ground application. Fertilize with the equivalent of 10 – 20 pounds of a 21% boron product per acre. Boron can be injected through micro-irrigation systems, broadcast or sprayed on the ground, or included in a herbicide spray. Herbicide sprays containing glyphosate may need to be buffered to prevent reduction of herbicidal activity. Hull levels over 200 ppm indicate excessive boron.

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David Doll0 commentsApril 29, 2010Nutrient

Tips for Maximizing Nitrogen Use Efficiency for Almond

Previously this week, I wrote an article discussing nitrogen needs within the almond orchard. Application of nitrogen, as briefly discussed, varies in efficiency based upon techniques of application and irrigation/fertigation systems. Below are some tips to maximize efficiency and reduce losses for many common fertilizer application strategies. Maximize Efficiency:1. Apply N only when leaves are present and the tree roots are active. Avoid dormant season applications.2. Efficiency can be increased by applying N in small doses more frequently than large doses less frequently.3. Apply a uniform irrigation that is adequate to carry the N into but not past the root zone.4. Because young fruit trees have a fairly constant N uptake, apply multiple applications of N throughout the growing season.5. Mature trees need most of the N in the spring, around 70-75% of the nitrogen budget.6. Late summer/postharvest applications, 25-30% of the budget,will help with flower bud differentiation and formation for next year’s crop.7. Fertigation has generally been very efficient in N applications.8. Analyze leaves in July each year to fine tune N level to the orchard. Maintain the level in the adequate range. Minimize Losses:1. If fertilizer is surface applied, disc or irrigate N into the root zone shortly after application.2. Fertilize the tree, not the covercrop. Evaluate how best to bypass the covercrop. This may be by applying the fertilizer to the herbicide sprayed strip, mowing, or cultivating the covercrop.3. Don’t over irrigate. Nitrogen is soluble and moves with water. Excessive runoff of tail water or leaching will remove N.

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David Doll4 CommentsMarch 26, 2010Nutrient

Nitrogen Content in a Gallon of UAN-32

I have been emailed a few questions in regards to calculating the amount of nitrogen in a gallon of Urea Ammonium Nitrate (UN-32 or UAN-32). Since UN-32 is widely used to fertilize/fertigate almonds, it is necessary to know how much is being applied per application. 1 gallon of UN-32 weighs 11.02 pounds. 32% of the weight is nitrogen – hence the “32.” This roughly equals 3.4 pounds of nitrogen per gallon, or 55 ounces. So, following the guidelines suggested by Brent Holtz (UCCE San Joaquin),when fertigating 2nd leaf trees with UN-32, at 110 trees/acre, no more than 4 gallons should be used in a single application. I hope this helps.

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Brent Holtz12 CommentsMarch 15, 2010Nutrient

Fertilizing one-year old trees – be careful!

Nitrogen is the most important element we can apply to our tree fruit crops. Almond growth and productivity depend on the availability and uptake of nitrogen. Most fertilizer recommendations are based on making nitrogen available to our trees so that a nitrogen shortage does not limit tree growth or productivity. Young almond trees don’t require as much nitrogen as older trees. I like Wilbur Reil’s rule of “one ounce of actual nitrogen per year of age of tree”. That rate can be applied several times per season, but never more than that at any one application. Thus, a first leaf (first year in your orchard) almond tree should not receive more than one ounce of actual nitrogen per any application. A five year old almond tree should not receive more than 5 ounces of actual nitrogen per one single application. The University of California only recommends one ounce of actual nitrogen per one year old tree over the course of the season, but I have been told by many growers and PCAs that this rate is not enough for the growth they desire. So, if you want to put out five ounces of actual nitrogen per one year old tree, do so in five applications and not all at once! I have seen many trees burned by nitrogen, especially if liquid fertilizers like UN-32 (urea ammonium nitrate 32 %) or CAN 17 (a clear solution of calcium nitrate and ammonium nitrate) are used in single applications. These liquid fertilizers are very effective and easy to use but it doesn’t take much to burn young trees. I do not suggest using these liquid fertilizers on first leaf trees–I prefer to see triple 15-15-15 (15% Nitrogen – 15% Phosphorous – 15 % Potassium) fertilizers used on first leaf trees. I like to

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David Doll7 CommentsDecember 21, 2009Nutrient

Making a Zinc Dormant Spray

Question came in this week regarding the decision on the timing of a zinc spray. When should I make a Zinc Spray?Research by UC Specialist Dr. Scott Johnson at the Kearney Agricultural Center has shown that a zinc foliar spray is the most effective when made during the post harvest period. Applications of zinc should be made to the tree around late October – early November. The idea is to have a leaves still on the tree when the application is made. Dr. Johnson has shown that a roughly 3% of the zinc applied is taken into the tree from a fall foliar spray, but this is dependant upon the source of zinc. Defoliation may occur after the application, but do not worry as sufficient zinc should have made its way into the plant tissues. Is making a dormant zinc application a bad idea?If a fall application of zinc was not made and the orchard is suspected to be deficient in zinc, making a dormant application of zinc will increase zinc tissue levels. The percentage of uptake is slightly less, around 2.0-2.8%, and it is harder to get a large amount of zinc into the tree. This is due to the fact that the shoots, buds, and bud scars only account for roughly 3% of the surface area of a peach/almond branch. Therefore the amount of spray landing on the tree surface is significantly less than when the leaves are still attached (Leaves make up the other 97% of the surface area). To counter this, higher rates should be used during the dormant period. What type of material should be used in a zinc spray?Dr. Scott Johnson’s (UC Specialist) work has shown that the “biggest bang” for your buck comes from Zinc Sulfate (high uptake, moderate phytotoxicity). There are other

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David Doll5 CommentsDecember 7, 2009Nutrient

Potassium Applications in Almonds

Having a major role in many plant processes, potassium promotes root growth, increases kernel/fruit size, and provides key metabolic features that include the formation of starch, translocation of sugars, stomata regulation, and the formation of xylem vessels. In general, plants deficient in potassium tend to have slow growth, with small, pale leaves. Trees that are severely deficient may have necrotic tips and margins. In many cases, the leaf tip curls upwards in a common symptom that is named the “Vikings Prow” (Figure 1). Since Potassium plays a large role in tree health, it is important to maintain proper levels of the nutrient within the tree. A critical leaf value of 1.4% has been established by the University of California and current research has suggested that levels above this value do not increase yields. Recent field studies by Roger Duncan (UCCE Stanislaus) have demonstrated that leaf potassium levels in excess of the 1.4-1.6% range did not increase yield. Through the study, leaf levels between 1.4-1.6% gave the best yield results, with yield decreasing when potassium levels were below this level. Leaf potassium levels higher than this range did not increase yield, and may actually reduce yields if applied in excess. Potassium usage by the almond crop is high. Upon harvesting the hulls and kernals, potassium is removed from the orchard. Studies by Dr. Patrick Brown (UC Davis), have shown that 76 pounds of potassium (92 lbs of K2O) are removed from the orchard for every 1000 pounds of kernals harvested. From nutrient analysis of the fruit parts, 70-80% of the potassium removed by the harvest is within the hull, while the rest is within the shell and kernel. Even though a large amount of potassium is used by the almond crop, it doesn’t always mean that large applications of potassium are needed

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Roger Duncan5 CommentsOctober 6, 2009Nutrient

Post-harvest Boron Applications Can Increase Almond Yields

Written by Roger Duncan, UC Farm Advisor, Stanislaus Boron deficiency is very common in orchards and vineyards planted on the eastern side of our county. This nutrient is essential in pollen tube growth and fertilization of the flowers. Moderate boron deficiency does not produce recognizable foliar symptoms but trees do not set their full potential of fruit. Boron tends to accumulate in almond hulls and thus hull samples provide a better indication of boron status than do leaf samples. Harvest is an easy time to sample hulls. If samples are collected much earlier than harvest, a false reading may be obtained because boron may continue to accumulate in the hulls as long as they remain green on the tree. The current boron guidelines for hulls are as follows: 80 ppm or lower = deficient 80-150 ppm = adequate Over 200 ppm = may be toxic Soil applications are the best way to correct a deficiency. Be very careful when applying boron—a little boron fertilizer goes a long way and will last for a few years. Soil applied boron fertilizers should be broadcast, not banded. Research has shown that even orchards with up to 120 ppm benefit from a post-harvest foliar application of boron. In University of California trials in Stanislaus and other counties, postharvest boron sprays often increased nut set and yield 20-30% the following year compared to non-treated trees. Timing: The goal of the foliar application is to get the boron into the flower buds (actually pollen tube mother cells) that are developing for the next year. Therefore, timing of application is very important. During the growing season (March through July), large quantities of boron go into the developing hulls. If foliar boron is applied at this time, most of the boron will go into the hulls and is

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