Posts Tagged: calcium

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

Blossom End Rot in Citrus - Another Result of Drought

Another impact of the drought? There have been reports of a sunken, leathery patch around the blossom end (opposite of the stem end) of citrus fruit. This has been reported on lemons, limes and mandarins, but I am sure growers are seeing it on oranges, as well as other citrus relatives. This is an abiotic problem caused by a lack of calcium to the fruit, a problem with the plant's growing conditions, not a disease. This is a serious disorder found in various fruits and vegetables, such as tomatoes, melons, peppers and eggplants

Blossom-end rot begins as small tan, water soaked lesions on the blossom end of the fruit. The lesion enlarges and becomes sunken, dark, and leathery. On peppers, the lesion is more commonly found on the side of the fruit towards the blossom end. Also, on peppers it can be sometimes confused with sun scald. Fruit infected by blossom-end rot ripen often become infected with secondary organisms such as Alternaria spp (most likely the surrounding tissue in the photo below).

This is a physiological disorder of low calcium in the fruit. Calcium is required for normal cell growth and in relatively high concentration for new tissue growth. Rapidly growing fruit will begin to breakdown at the blossom end because that is the last place of the fruit tissue to receive calcium and also the area with the lowest concentration of calcium.

In rapidly growing plants, calcium cannot move to those rapidly growing areas quickly enough. Because calcium moves with water, fluctuations in water supply can cause blossom-end rot. Large fluctuations in soil moisture inhibit uptake and movement of calcium within the plant. Excessive nitrogen promotes rapid plant growth, which can cause low concentrations of calcium to occur in plant tissue. Leaf tissue can often not disclose a low calcium in fruit because of the lag in movement of calcium to the rapidly growing fruit tissue.

Other causes such as low calcium levels in the soil or high amounts of cations in the soil which compete with calcium uptake can also cause blossom-end rot. This is especially true in areas of soils derived from serpentine rock that are high in magnesium. The magnesium competes with calcium uptake.

Proper fertilization and water management help to minimize this problem. Avoid over fertilizing the crop. Also avoid allowing the soil to become too dry and then overly wet. Wide fluctuations in soil moisture inhibit calcium uptake and movement. If calcium is deficient or high salts occur in the soil, gypsum applications can help, but delayed uptake may not help fruit tissue content. Often, foliar applications of calcium may be beneficial.

blossom end rot lemon

Silicon as a Nutrient for California Fruit Trees

Silicon is currently under consideration for elevation to the status of a "plant beneficial substance by the Association of American Plant Food Control Officials (AAPFCO). Silicon has been shown in university and field studies to improve cell wall strength and structural integrity, improve drought and frost resistance, decrease lodging potential and boost the plant's natural pest and disease fighting systems. Silicon has also been shown to improve plant vigor and physiology by improving root mass and density, and increasing above ground plant biomass and crop yields.

Silicon (Si) is the most abundant element (27.2%) present in the earth's crust following oxygen (45.5%). Silicon is known for a number of important chemical and physical properties, i.e. semiconductor property that are used in various scientific and technical applications. In most soils near a neutral pH, the composition is a complex of iron, aluminum, oxygen and silicon. Silicon is one of the most important constituents of dust, which is carried by winds all over the world. Geologists know silicon as the rock quartz and the many silicate materials, such as opal. Formally, silica (SiO₂) is a silicic acid (H₄SiO₄), which is water soluble and stable in highly dilute aqueous solutions.  There are many forms that silicon can take in the natural environment, often complexed with water.  Plants take up a form of silicic acid and in highly leached, low pH environments, much of the silicon may have been removed over time. 

It appears that grains, such as wheat and especially rice have an absolute need of supplemental silicon to improve plant growth.  Few non-grass plants have shown this need other than cucurbits apparently.  Much of the improvement typically is for improved disease control and improved stature (prevention of lodging).

Many of the studies showing benefits of silicon amendment have occurred in low soil pH environments or in solution culture where it has been possible to create low silicon growing media.  Several years ago, potassium silicate was being promoted as a fungistat for controlling Phytophthora root rot in avocado.  A number of field and greenhouse trials were tried in California during the early 2000s to assay its effect.  For whatever reason, the material showed no effect on the disease.  Potassium and calcium silicates are liming materials, raising soil pH.  The effect that was noticed in its use in other countries may simply have been a soil pH effect on either the avocado tree, the Phytophthora or both.

silicon

Salt and Gypsum

With the drought our perpetual salt problems are exacerbated due to less water and often more saline water.  The question keeps coming up if gypsum (calcium sulfate) can help correct the problem.  And the answer is maybe, but along the coast, probably not.  The problem there is confusion about what is a saline soil and what is a sodic soil.  A saline soil is one that is dominated by salts, but has a pH below 8.5 and can have a white crust that will actually taste salty.  A sodic soil is one dominated by sodium, has a pH above 8.5 and can be saline, as well.  Often though, there is a brownish cast to the surface salt crust.  This is caused by dispersion (dissolved) of soil organic matter caused by the high pH.  It's like cooking with vinegar when you make ceviche out of fish.  Saline soils often have a high calcium content and may have sodium, but at a very low ratio compared to calcium.  Most of the sodic soils in California are found in the Central and Imperial Valleys.  Along the coast, the soils, if they have a problem, are largely saline.

The way gypsum works, is that the added calcium displaces soil sodium, pushing it lower in the soil column.  The process also requires a lot of water to move the sodium through the soil column.

So the answer is, along the coast, gypsum is unlikely to improve soil conditions.  However, there are other instances where it might help. In the San Luis Obispo area there are lots of serpentine derived soils that have a high magnesium content relative to calcium.  And they commonly aren't saline, just an imbalance between the two cations. This can lead to infiltration problems and calcium deficiency in plants.  Apples are especially sensitive to this high Mg:Ca ratio and develop a condition called “bitter pit”, a surface, brown pitting in the skin. There are other crops, like celery that are especially sensitive, but even avocado can be mildly affected. In the case of magnesium imbalance, gypsum can help.

sodic-crust stutsman-co

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