Posts Tagged: boron
Pre-bloom foliar boron application on olive may improve yield
Olive orchards entering an OFF year in 2024 may benefit from pre-bloom foliar boron (B)...
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Drought Induced Problems in Our Orchards
Drought Induced Problems in Our Orchards
Abiotic disorders are plant problems that are non-infective. They are not caused by an organism, but through their damage, they may bring on damage caused by organisms. Think of a tree hit by lightning or a tractor. The damage breaches the protective bark which allows fungi to start working on the damaged area, eventually leading to a decayed trunk. It was the mechanical damage, though that set the process in motion.
Too much or too little water can also predispose a plant to disease. Think of Phytophthora root rot or even asphyxiation that can come from waterlogging or too frequent irrigations.
Salinity Effects from Lack of Water
Lack of water and especially sufficient rainfall can lead to salinity and specific salts like boron, sodium and chloride accumulating in the root zone. This happens from a lack of leaching that removes native soil salts from the root zone or the salts from the previous salt-laden irrigation from the root zone. These salts cause their own kind of damage, but they can also predispose a tree to disorders, disease and invertebrate (insect and mite) damage.
Lack of water and salt accumulation act in a similar fashion. Soil salt acts in competition with roots for water. The more soil salt, the harder a tree needs to pull on water to get what it needs. The first symptom of lack of water or salt accumulation may be an initial dropping of the leaves. If this condition is more persistent, though we start to see what is called “tip burn” or “salt damage”. Southern California is tremendously dependent on rainfall to clean up irrigation salts, and when rain is lacking, irrigation must be relied on to do the leaching
As the lack of leaching advances (lack of rainfall and sufficient irrigation leaching) the canopy thins from leaf drop, exposing fruit to sunburn and fruit shriveling.
Leaf drop and fruit shriveling in avocado.
In the case of sensitive citrus varieties like mandarins, water stress can lead to a pithy core with darker colored seeds, almost as if the fruit had matured too long on the tree.
Total salinity plays an important factor in plant disorder, but also the specific salts. These salts accumulate in the older leaves, and cause characteristic symptoms that are characteristic in most trees. Boron will appear on older leaves, causing an initial terminal yellowing in the leaf that gradually turns to a tip burn.
Often times it is hard to distinguish between chloride, sodium and total salinity damage. It is somewhat a moot point, since the method to control all of them is the same – increased leaching. There is no amendment or fertilizer that can be applied that will correct this problem. The damage symptoms do not go away until the leaf drops and a new one replaces it. By that time hopefully rain and/or a more efficient irrigation program has been put in place.
The Impact of Drought on Nutrient Deficiencies
Salinity and drought stress can also lead to mineral deficiencies. This is either due to the lack of water movement carrying nutrients or to direct completion for nutrients. A common deficiency for drought stressed plants is nitrogen deficiency from lack of water entraining that nutrient into the plant.
This usually starts out in the older tissue and gradually spreads to the younger tissue in more advanced cases.
The salts in the root zone can also lead to competition for uptake of other nutrients like calcium and potassium. Apples and tomatoes are famous for blossom end rot when calcium uptake is low, but we have also seen it in citrus. Low calcium in avocado, and many other fruits, leads to lower shelf life. Sodium and boron accumulation in the root zone can lead to induced calcium deficiencies and increased sodium can also further lead to potassium deficiencies. Leaching can help remove these competitive elements.
Drought Effect on Tree Disease
Drought and salt stress can also lead to disease, but in many cases once the problem has been dealt with the disease symptoms slowly disappear. They are secondary pathogens and unless it is a young tree (under three years of age) or one blighted with a more aggressive disease, the disease condition is not fatal. Often times, in the best of years, on hilly ground these diseases might be seen where water pressure is lowest or there are broken or clogged emitters. The symptoms are many – leaf blights, cankers, dieback, gummosis – but they are all caused by decomposing fungi that are found in the decaying material found in orchards, especially in the naturally occurring avocado mulch or artificially mulched orchards. Many of these fungi are related Botryosphaerias, but we once lumped then all under the fungus Dothiorella. These decay fungi will go to all manner of plant species, from citrus to roses to Brazilian pepper.
Another secondary pathogen that clears up as soon as the stress is relieved is bacterial canker in avocado. These ugly cankers form white crusted circles that ooze sap, but when the tree is healthy again, the cankers dry up with a little bark flap where the canker had been.
Drought Effect on Pests
Water/salt stress also makes trees more susceptible to insect and mite attack. Mites are often predated by predacious mites, and when there are dusty situations, they can't do their jobs efficiently and mites can get out of hand. Mite damage on leaves is often noted in well irrigated orchards along dusty picking rows
Many borers are attracted to water stressed trees and it is possible that the Polyphagous and Kuroshio Shot Hole Borers are more attracted to those trees.
And then we have conditions like Valencia rind stain that also appears in other citrus varieties. We know it will show up in water stressed trees, but we aren't sure what the mechanism that causes this rind breakdown just at color break. Could it be from thrips attracted to the stressed tree or a nutrient imbalance, it's not clear?
Water and salt stress can have all manner of effects on tree growth. It should lead to smaller trees, smaller crops and smaller fruit. The only way to manage this condition is through irrigation management. Using all the tools available, such as CIMIS, soil probes, soil sensors, your eyes, etc. and good quality available water are the way to improve management of the orchard to avoid these problems.
Scroll down for Images
Tip Burn, notice sun burn bottom right hand fruit
Endoxerosis with dried out core
Boron toxicity
Nitrogen deficiency
Blossom end rot
Potassium deficiency
Bot gumming in lemon
Black Streak in Avocado
Bacterial Canker
Citrus red mite
Polyphagous Shot Hole Borer damage on avocado
Valencia Rind Stain
avocado drought canopy
nitrogen deficiency
endoxerosis 4
boron toxicity citrus 1
blossom end rot lemon
potassium deficiency avocado
gumming dothiorella
avocado black streak 1
bacterial canker avocado
citrus red mite
PSHB damage
One, one hundred, one thousand
This little mnemonic, or memory aid, in the title is helpful in remembering the critical levels of toxic constituents in irrigation water. The “one” stands for 1 part per million (ppm) of boron (B), the e” hundred” flags 100 ppm of sodium (Na) and (Cl) and the “thousand” represents the level of total soluble solids (TDS or slats) in water. Levels exceeding the critical values for any of these constituents can present problems for tree growers. The problems typically show themselves as tip-burn and defoliation. The B, Na and Cl are toxic elements at relatively low concentrations, but symptoms appear similar to the damage caused by high salinity.
Water that exceeds the critical levels mentioned in the mnemonic has a greater tendency to cause damage if sufficient leaching is not applied. It doesn't mean the water is impossible to use, only that greater attention needs to be made to ensure that these salts are adequately leached. High levels of these salts accumulate in the soil with each irrigation, and the salts are absorbed by the tree and end up in the leaves where they do their damage.
This promises to be another low rainfall year and the customary leaching we rely upon in winter rainfall is not going to be as effective as in customary years. Irrigation is a necessary evil. Every time we apply irrigation water we apply salts, and unless some technique is used to minimize salt accumulation, damage will result. This damage can be more than just leaf drop, but also the stress that induces conditions for root rot.
Irrigation water has been applied the last four years and many trees looked stressed. Even well irrigated orchards have leaf burn due to the gradual accumulation of salts from irrigation. It is probably necessary to irrigate in many winters. With the lack of rain problem, it may be necessary to irrigate even if there is rain. The wetted pattern that is created by a drip or microsprinkler emitter also creates a ring of salt in the outer band of the wetted patter. If there is less than an inch of rainfall to push this salt down, this salt tends to diffuse towards the tree where it can accumulate back in the root system. Orchards with even good water quality would find it advisable to run the irrigation system with the first rains. Growers with water quality exceeding one, hundred, or thousand should be especially alert to the need to manage water in low rainfall years.
irrigATING CITRUS
Problems Growing Avocadoes in a Container
Help for the Home Gardener from the CCMG Help Desk
Client's Questions and Problems:
with some webbing as well as some “corky” bark. He also said they have “red ants” on the tree which bite when handled. The container is large, and consists of a mixture of native (clay) soil and amendments. He has poor drainage in his yard hence the need for container. Has plans to plant another variety (Zutano) so will have the A and B pollinators. Varieties are compatible and appropriate for his area. Client uses well water and is close to Discovery Bay and knows about their boron problem, but his well seems fine although he has not taken a recent water test.
CCMG Help Desk Initial Response:
Thank you for calling Master Gardeners with your Avocado problems. The e-mailed photos came through well. Based upon the information so far, we think the most likely cause of the brown areas on the leaves is sunburn and/or windburn. You may have noticed that the affected leaves are mostly on the top and outside of the plant, and there are many unaffected leaves. We have had a few really hot days in recent weeks (these questions and responses are in mid-September). You can provide some temporary shade using a light shade cloth or some other shade structure on hot afternoons - although hopefully we will not have too many more of those to come this year. Also, avocados are quite sensitive to wind, so if they are in a windy area some protection from wind might help. You mentioned that the tree is getting adequate water, and from the photos I did not see problems related to well water - although it may be helpful to get that tested if you see other plants in your garden developing problems. I did see some webbing on the leaves, but it does not seem to be widespread in the tree. I could not tell from the photo if there were insects present, but it could be spider mites, and if this insect presence is only in a small area of the tree, you can wipe them off or use a quick water spray. I am including some UC links which will give some more information on pests and on avocados in general. http://ipm.ucdavis.edu/PMG/GARDEN/FRUIT/avocados.html and http://ipm.ucdavis.edu/PMG/PESTNOTES/pn7405.html
You also mentioned that you had a colony of 'red ants'. Without seeing these I cannot tell you what they are; red fire ants have been found in southern California, and I have not heard reports of them being in the Bay Area, but that does not mean you don't have them. What you are seeing could be red Spider Mites. Here is a link that might help-http://ipm.ucdavis.edu/PMG/PESTNOTES/pn7487.html
If you would like a positive identification on these ants, you could bring a sample into the Agricultural Commissioner's office, of which there is a branch in Knightsen. This link gives their hours and contact information.
http://www.co.contra-costa.ca.us/1542/Agriculture-Weights-Measures
Finally, here are some further links to general avocado culture. The second one has some good information on growing in containers. http://ucanr.org/sites/gardenweb/files/29079.pdf
and http://uccemg.com/Edible_Plants/?ds=530&uid=127
I hope this is helpful, and that you will eventually grow some good avocados.
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CCMG Help Desk Follow-up Response:
After we spoke earlier today, I did some research and learned that avocados are very sensitive to high salt (chloride) and boron levels in irrigation water. Symptoms of chloride toxicity include chlorosis (yellowing) of leaves and necrosis (death) of the tips and margins (edges) of leaves. Symptoms are usually more severe on the older leaves. Boron toxicity causes dark, necrotic areas along the edges of leaves.
Here is a University of California photo that shows how boron toxicity appears on an avocado (left). The right photo shows chloride toxicity effects on an avocado.
Boron Toxicity
Chloride Toxicity
The damage on the leaves in these photos look similar to those in the photos you sent previously, so it does seem possible that high levels of salt or boron in the irrigation water could be causing the leaf problems you are seeing on the tree. It is probably worthwhile for you to have the water tested for the well you are using to irrigate the tree. There is the possibility that the drought, or increased (or decreased) pumping of other nearby wells, or changed irrigation practices have affected the quality of your well water.
A list of commercial laboratories that perform water testing can be found at this link on the CCMG web page (http://ccmg.ucanr.edu/files/77177.pdf). You will want to have the water tested for irrigation suitability. It is sometimes hard to navigate the websites for the testing labs and to find a description of the services offered and the charges for the testing they can perform. You might find it easier to call the labs to get the information you need. Be sure to call several before you decide which one to use since the fees charged seem to vary quite a bit. I found a couple that charge only about $75 for the irrigation water test, but some charge twice that much.
Below is an excerpt from tables from the University of California publication entitled "Abiotic Disorders of Landscape Plants" (the original reference document's Table of Contents is at http://www.fao.org/docrep/003/T0234E/T0234E00.htm#TOC) that you might find helpful in understanding the results of your well water test. The data from the tables show maximum levels of salts (chloride) and boron in irrigation water that are generally considered safe. Because the avocado is quite sensitive to boron and salts, any amounts in your well water that are higher than the levels shown below n the table as “generally safe” could cause problems for the tree. If you have the water tested and would like some assistance in interpreting the results, you are welcome to contact us for help.
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Relative Boron Tolerance of Avocadoes: Sensitive @ 0.5 - 0.75 mg/l
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Maximum Permissible Chloride Without Avocado Leaf Injury from Different Rootstock
Root Stock Root Zone (Cle) (me/l) Irrigation Water (Clw) (me/l)
West Indian 7.5 5.0
Guatemalan 6.0 4.0
Mexican 5.0 3.3
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On a different topic, I looked again at the photos showing the rough, “corky” areas on the bark of the tree. It does look somewhat unusual, but I couldn't identify any likely causes. When I tried to enlarge the photo to look closer at the corky areas, the photo became blurry. If you want us to investigate further, perhaps you could send us a “close-up” photo. Also, one possibility that occurred to me is that it might be sun scald. You might want to check to determine whether the side of the tree that receives the most direct sunlight shows more of the rough corky areas as compared to more shaded areas. If the answer is “yes”, it could point to sun scald.
Hope you find this additional information to be helpful. Feel free to call us again if you have additional questions.
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Contra Costa Master Gardeners' Help Desk
Editor's Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523.
We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/
Water Quality and Southern California Agriculture
Assessing water quality for Southern California agriculture typically revolves around the total salinity of the water, its total dissolved solids (TDS), and the toxic ions boron, sodium and chloride. Salts are necessary to plants, because it is in the form of diluted salts that all nutrients are taken up by plants- the macro and micronutrients plants extract from the soil. High salinity leads to water imbalance problems much as if the plant were not getting adequate water. A toxicity problem is different from a salinity problem, in that toxicity is a result of damage within the plant rather than a water shortage. Toxicity results when the plant takes up the toxic ions and accumulates the ions in the leaf. The leaf damage that occurs from both toxicity and salinity are similar in that it causes tissue death known commonly as "tip burn." The damage that occurs depends on the concentration of the ions in the soil water around the roots, the crop sensitivity and crop water use, and the length of time the crop experiences the ions. In many cases, yield reduction occurs. Because crops can not excrete salts the way humans do, salts gradually accumulate in a plant. As a result plants need a higher water quality than humans do.
Much study in many countries has gone into evaluating water for crop use. Some of these studies have been on the effects of salts on soil characteristics. Generally, as sodium concentration increases, a soil will lose its aggregation, eventually leading to poor water infiltration. Many more salinity and toxicity studies have been done on plants themselves. Not all crops are equally tolerant of salinity and toxicities, and in general most plants respond to salinity and toxicities in a similar fashion. If a plant is intolerant of salinity, it will be intolerant of chloride, sodium and boron. Most annual crops are less sensitive to salts than tree crops and woody perennials, although symptoms can appear on any crop if concentrations are high enough. The reason for greater sensitivity for perennial crops is that the tree is sitting in the ground absorbing salts for a longer period than the lettuce plant that is harvested 3 months after planting. Furthermore, deciduous trees like walnut shed their leaves each winter, so they can handle salinity better than evergreens like citrus and avocado.
To manage salinity and toxicities, water management is the key. Depending on water quality, an excess of water will be applied to the soil to leach the previously applied salts away from the root zone. The poorer the water quality, the more excess water is applied.
Selecting a less sensitive crop is also an alternative when dealing with poor water quality. Some barley varieties can handle salinity similar to ocean water. Barley nets a grower $400 an acre, avocados $9,000 and $25,000 if the market is right for strawberries. Avocados are salt sensitive, so are strawberries and lemons and cherimoyas and star fruit and blueberries and raspberries and mandarins and nursery crops. We grow these because with our climate, very few other places can grow them and they return enough money for a grower to stay in business in an area where land, water and labor are expensive. We really don't have much in "alternative crops" to grow here.
avocado fruit