Several articles have been posted on the importance of boron. These have highlighted the importance of boron for fruit set, reliance on hull sampling for tree boron status, and foliar applications.
In regards to these posts, I have received several good questions that I thought I would share.
Q. When should I apply boron to my field?
A. The hull serves as a sink for boron. Applications made after the fruit is removed will be more effective in increasing boron levels within the tree. The nutrient will require transpiration in order to move throughout the tree, and therefore ground applications made in the dormant season will have minimal effect on the coming year’s crop, but will impact the next, next year crop. In other words, an application made in January 2015 will provide the most benefit to the 2016 crop. I should add that an application in the 2015 dormant should increase boron applications in 2015 hull samples – it just will not be in the fruit bud of the tree until 2016.
Q. What about foliar sprays, and do I need them?
A. A foliar spray made between post-harvest and pink bud has been shown to increase yields. This is an effective way to increase boron levels within the tree. Unless boron hull levels are over 150 PPM, foliar sprays are recommended. Low rates should be applied.
Q. What about if my water or soil contains boron?
A. Boron can be a toxic salt at too high of a level. If soil or water levels are too high, boron should not be applied. Again, hull analysis for boron should indicate if the tree is requiring boron. Boron levels within soil will eventually reduce if applications by irrigation water or fertilizer are eliminated.
Q. Does boron leach?
A. Yes. Boron will leach at different rates depending upon soil textures. Soils with lower exchange capacities should make smaller, more frequent soil applications (~10-15 lbs of solubor/acre), while soils with higher exchange capacities may suffice with larger applications (~15-20 lbs solubor) every other year.
Q. How much boron is used by the tree?
A. This is dependent upon hull concentration and crop load. Keep in mind that boron is in greatest concentration in the hull, and hull removal amounts are typically double that of kernel yields (e.g. a 2000 lb/acre crop removes 4000 lbs/acre of hulls). In regards to removal, the following table indicates rates of removal for 1000 kernel lbs for various hull boron levels:
Hull Boron Content (PPM) | Lbs of Boron Removed per 1000/kernel lbs |
75 | 0.15 |
100 | 0.2 |
125 | 0.25 |
150 | 0.3 |
200 | 0.4 |
300* | 0.6 |
500* | 1 |
*These levels are considered toxic within almond.
Alan McDonald
September 20, 2014Can the hulls be safely returned to the soil in order to recycle the boron and other nutrients? Alternatively, can they be cultivated into say Olives which also require reasonable boron levels?
David Doll
September 21, 2014Yes, we believe they can. They are also a great source of potassium (~3% K). Within CA, hulls serve as a source of cattle feed – a byproduct in which they have considerable value (~$150-175/ton), which explains why it isn’t done in CA orchards.
Ernie
September 21, 2014I applied boron during the fall of 2013, my hull samples for 2014 show a low level. Should I hold off on applying any more boron because it takes a year to see the results from the 2013 application ? Thanks
David Doll
September 21, 2014Ernie,
Good question. I made a bit of a mistake – what I meant to say is that boron applied in the dormant will not be present in the buds at bloom. It will, however, move into the hull in the season. I fixed the article to reflect this.
This means that you should consider another boron application if tissue concentrations aren’t above 80-90 ppm.
David
lee
September 25, 2014I would like to know when and almond is on the tree and into mid to late late stage will the outside skin smell like a peach. I am not sure I have a almond tree. Could you give me an answer thank you Lee
David Doll
September 30, 2014Yes, lee, it can have a “peachish” smell. Generally, the hull of an almond will split open while it wont for a peach.
David
Paul
September 30, 2014Could you please provide some recommendations or references for foliar application. I am planning my routine late season foliar nutrient applications on my sandy-soil young-orchard.
I would like to figure out how much and what form of Boron to add. And if I can add it to an existing foliar nutrient application or split it up..
David Doll
September 30, 2014Paul,
Generally, foliar applications are very low rates – typically around .2-.4 lbs of actual boron in 100 gallons of water. This is equivalent to 1-2
2-4lbs of a 20% boron product (e.g. Solubor). More can be found in this earlier article. In regards to compatibility – that is not an easy question as it depends on formulations and other nutrients applied. I haven’t heard of many issues with compatibility with boron products, but if applying 3-4 products, a bottle test might be warranted.David
Josh
October 29, 2014Can a grower spray multiple boron sprays in the fall, or one in the fall and one at pink bud, to further increase the boron levels in the flower bud in a boron deficient (65ppm 2014 hull test) orchard to benefit the 2015 crop. Would this create toxicity in the flower bud? We already sprayed once, applied boron through drip in the fall and were wondering if a pink bud spray would be beneficial? Thanks
David Doll
October 30, 2014Josh,
A single spray should do the trick. If possible, a lighter dose now and one at pink bud may be of benefit (0.2 lbs of actual boron/100 gallon of water per acre). If not possible to run the rigs through, I would apply the higher end of the application – 0.4 lbs of actual B/acre.
You made the right call on applying boron to the soil this fall. It should be reflected in next year’s hull analysis.
David
Jack Efird
September 1, 2018I have high levels of Boron (2-3 times) in my soil and deep well pump in my almond orchard.
I use ditch water when it is available for leaching but it is heavier soil.
Will the application and availability of Calcium displace the uptake or use of Boron by the plant? If so, how much Ca, in the form of gypsom, should I use? Is there a ratio or is the concrete that the more Ca available, the less the Boron the plant will take up?
Where can I learn more on the steps I can use to minimize an excess Boron issue?
Thank you
JE
David Doll
September 13, 2018Dear JE,
These issues are very complicated. I would reach out to your local extension advisor to review your soil and water reports to determine the optimal strategy. If in Fresno County, check out the website cefresno.ucanr.edu for the contact details for your advisor.
David
Rod Vilas
October 9, 2019Question on hull sampling for testing boron levels. Are there any differences in levels between different varieties in the orchard. Should the hulls being selected be from a certain area or height of the tree? And finally, what amount of variance in readings (ppm) is expected from one year to the next?
I pulled samples from multiple orchards this year, and my results came back in the 50-60 ppm range. Last year these same fields ranged from 95-150 ppm. We had the test re-ran and came back the same. Then we took a couple samples from two of the same fields to another lab, and the results came back at 97 ppm and 116 ppm, which were down around 40ppm from last year results for those two fields.
David Doll
November 1, 2019Rod,
Wow, I dont know how to answer this as there potentially may be a few issues occurring. The three issues I would keep in mind is soil type, sampling variability and lab quality. Soils that are prone to leaching, such as sands or loamy sands with low cation exchange capacities, may have large swings in boron levels if not applied regularly. In these types of soils, I always feel it is best to apply 10 lbs of a 20-21% boron product annually to maintain levels. When it comes to sampling, samples should be pulled from similar heights, with hulls coming from multiple trees in the field. The more trees that are sampled within the field, the more representative the results will be of that field. Following a similar pattern as what is used to sample leaves would be best – that is 20-25 trees at least 100 yards apart. As far as the lab sampling, using a high quality lab will help. Even so, errors may occur due to poor processing. Occasionally, it might be best to grind a sample of hulls within an old coffee grinder, uniformly mix, divided into 4-5 samples and then sent to the lab to process. If the results are within a similar range (they probably wont be exact), it should give you an idea that the lab is maintaining good precision.
Finally, keep in mind that low bearing trees tend to have higher hull boron levels while high bearing trees will be lower. If hulls were selected from a tree that an ‘off’ year, it may skew the results.
David
I hope that helps.
Rod Vilas
April 15, 2020Thanks David. Also, is after fruit removed the best time to apply soil applications of Boron?
David Doll
April 17, 2020Rod,
Boron can be applied to the soil nearly anytime of the year. In saying that, however, there have been a few situations in which an application in the summer led to an increase in stick tights with obvious gumming at the peduncle and no hull rot. I would probably split my soil boron applications – 1/2 in the late spring, 1/2 in the postharvest to make sure it is present within the soil through the season.
David
Carol Kelley
August 25, 2020Where can I buy boron for my almond tree? I live in willows. CA.
David Doll
August 31, 2020Dear Carol,
If it is a single tree, I would probably buy a box of borax from the grocery store. The tree would only need about 1/2-1 cup of the material sprinkled around the base of the tree (more is not better!). The remainder can be used for the laundry!
David
Giovanni Damato
October 12, 2020I have read the answer to Paul of Sep. 30, 2014 regarding foliar application of boron:
“Generally, foliar applications are very low rates – typically around .2-.4 lbs of actual boron in 100 gallons of water. This is equivalent to 2-4 lbs of a 20% boron product (e.g. Solubor)”
2lbs x 20 : 100 = 0.4 lbs of actual boron
4lbs x 20 : 100 = 0.4 lbs of actual boron
I misunderstood, I mispmuted or the % of actual boron is at 10%.
Thanks Gio
David Doll
October 26, 2020Gio,
Hope you are doing great. Great question and you caught an error! It should read 0.2-0.4 lbs/acre of applied B (1-2 lbs of B per acre).
I will correct the article.
Thanks for the help,
David