Posts Tagged: phosphorous

P a Simple Little P

It is such a simple little letter, P. It stands for the element phosphorus. It is often misspelled as phosphorous which is an adjective, but even in technical literature it is misspelled. But that's not the end. Phosphorus is an element that takes many forms called oxidation states. When it is in the form of phosphate or phosphoric acid, it is a fertilizer – H₃PO_4. But when it is in the form of H₃PO₃ or phosphonate or phosphonite or phosphite or phosphorous acid, it does not perform like a fertilizer. It acts more like a stimulant for a plant to fight off Phytophthora or Pythium. And it works well for avocado and citrus root rots, as well as citrus brown rot.

But a grower recently told me that there is no end of confusion about these two very different forms of P.

A recent article helps to clear up some of this confusion

http://www.spectrumanalytic.com/support/library/pdf/Phosphites_and_Phosphates_When_distributors_and_growers_alike_could_get_confused.pdf

and more if you are still interested

https://edis.ifas.ufl.edu/hs254

 

Sick avocado on the left and healthy on the right

root rot vs healthy

Phosphorous Acid Confusion

It is more than just the confusion about the effects of phosphonates, but also how to spell the words associated with the P atom. Phosphorus with an ending in “us” is the element we know as P, while Phosphorous with a “ous” ending is the adjective of P. So an acid containing Phosphorous acid is written H3PO3 while phosphoric acid is H3PO4. These are both strong acids and can hurt and cause damage if splashed on the skin. When either is reacted with calcium or potassium hydroxide, a salt is formed which is less dangerous to users, but as with any chemical can be misused.

The salt formed from Phosphorous acid is called calcium phosphite or calcium phosphonate depending on what naming system is used to describe it. Whereas when these bases are reacted with phosphoric acid, the result is calcium or potassium phosphate. These salts are relatively benign in contact with skin. Labels on containers often call phosphorous acid, “soil applied” whereas the phosphite forms are called “leaf applied”. The “soil applied” when applied to a leaf can cause damage, whereas, the leaf applied is much less likely to cause damage to both plant and applicator. It can be applied to the soil, as well. It's much safer to use the leaf applied in either application technique.

The phosphites are often registered as fertilizers, but they have little nutrient effect. Most of their effect is to boost the plant's immunity to Phytophthoras and pythiums. This is called fungistasis and the material is called a fungistat. They don't act as a fungicide when normally applied to kill these organisms.

So you can see there is a lot of confusion in the phosphorous world. Knowing the proper spelling, pronunciation and use is note only good grammar, it makes good farming.

To read more, see:

http://plantscience.psu.edu/research/centers/turf/extension/factsheets/phosphonate-products

https://edis.ifas.ufl.edu/hs254

http://grammarist.com/spelling/phosphorous-phosphorus/

 

There are few documented cases of phosphorus (P) deficiency in tree crops in California.

p deficiency in citrus

Are All Phosphorous Products the Same

South African plant pathologists were the first to show that root rot in avocado could be controlled by trunk injection with both phosphorous acid and the patented material Aliette®.  Aliette was briefly registered in California in the late 1980’s, but theregistrant soon lost interest in pursuing a full pesticide registration when it became apparent that other researchers believed phosphorous acid could be registered as a fertilizer - a process much less costly and simpler than a pesticide registration. The company continued to hold on to the patents for the product and the breakdown products that were useful in root rot control.  By holding onto the patent, this effectively stopped other companies from pursuing a pesticide registration for phosphorous acid.    In 1990, a publication reported that phosphite could be used as a source of phosphorus fertilizer and this became the basis for the registration of phosphite as a fertilizer.  Subsequently, when the original patent expired, at least two materials have been registered as fungicides containing phosphite – Fosphite® and Agri-fos®.  There are, however, numerous phosphite materials that have been registered as fertilizers (for some brands see Brunings et. al., 2005, http://edis.ifas.ufl.edu/HS254), and every day seems to bring more brands onto the scene each making claims of having the best efficacy.

 

We wanted to see if we could detect an efficacy difference between Aliette, another registered phosphite fungicide and four different materials registered as fertilizers, for a total of six materials.  In a greenhouse, three-month old ‘Topa Topa’ seedling avocados with cotyledons removed were planted into a Phytophthora cinnamomi -inoculated organic potting mix. A control was also planted without the inoculum, as well as an inoculated control.  One of six different materials was then applied as a soil drench until draining from the bottom of the liner.  The materials were applied at the equivalent phosphorous acid concentration.  There were 20 replicates for each of the controls and treatments.  The experiment was repeated twice.

 

At harvest, root fresh and dry weights were highest for the non-inoculated trees and lowest for the untreated, inoculated controls, in both trials.  All treatments’ associated weights intermediate between these two were statistically the same.  Even a repeat application of one of the treatment materials in trial II didn’t result in greater root weights than single application treatments.  Shoot weight, both dry and fresh, was much less affected by root rot and treatments.  There were no differences in fresh shoot weight in the second trial, not even between the inoculated and noninoculated controls.  The root and shoot weights of all the treatments in the second trial were higher than in the first trial, indicating that either the inoculum was not as effective or that the trial was not continued long enough to produce as much damage.  

 

Root rot studies often have dramatic effects on root weights while shoot weights may remain little affected.   It is clear from our data that phosphites reduced the severity of root rot in this study, but that there was no benefit of a single source of phosphite relative to any other source.  

Below:  Healthy and decaying avocado roots.

avocado RR picture

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