Phosphorous Acid is very different than Phosphoric Acid
 

Phosphorous acid = H3PO3 (Also known as phosphate) As in Agri-Fos and Plant Doctor (formally Exel LG)

Phosphoric acid = H3PO4 (Also known as phosphorus) The “P” component in NPK fertilizers

More on this here by amideutch[B] [URL]http://www.tomatoville.com/showpost.php?p=132308&postcount=7[/URL][/B]

I do believe at one time Agri-Fos and Exel LG were both ORMI certified. My guess is that someone put the idea in the heads of some people in the ORMI sanctioning body that H3PO3 and H3PO4 were similar. In reality they are no more similar to each other then carbon dioxide is to carbon monoxide.

Carbon Dioxide = CO2 – All animals breathe this out and all plants take this in great quantities.

Carbon Monoxide = CO – Deadly to all animals and plants at anything above 667 parts per million.

What a different one little number can make!!!

Dutch

I usually keep a gallon of Ospho around the house.
It is 75% phosphoric acid.

The stuff works wonders.
[IMG]http://fiberglasssupplydepot.com/images/P/ospho.jpg[/IMG]

A couple correction Dutch.

Phosphorous acid (H3PO3) is also known as [B]phosphonate[/B], not [B]phosphate[/B].
Pure Phosphorous acid is not used as a fungicide since it is such a powerful reducing agent, it would kill plants. It is always sold as a salt, usually as Potassium salts.

Phosphoric acid (H3PO4) is also known [B]orthophosphoric acid[/B] , not [B]phosphorus[/B])
Phosphoric acid is highly corrosive in the concentrations like Worth uses. Phosphoric acid isn't common naturally in soil and cannot be used by plants, but in the soil it will convert to hydrogen phosphate (HPO42-) and/or dihydrogen phosphate (H2PO4-) which are the forms plants can use.

More info [URL="http://edis.ifas.ufl.edu/hs254"]here[/URL]

Thanks Ray and yes I agree with you that Phosphorous acid (H3PO3) when used in fungicides it is typically in a salt form. I supplied a link in my original post and stated that it provided more information.

Agri-Fos, which I purchased locally at an independent farm supply and feed store, states this on the label;
Active Ingredients:
Mono- and di-potassium salts of Phosphorous Acid 45.8%
Other Ingredients 54.2%

Monterey Aliette, the original Phosphorous acid based fungicide states this on the label;
Active Ingredient – 0-Ethyl Phosphonate 80%
Inert Ingredient – 20.0%

Exel (Organic Laboratories), states this on the label;
Active Ingredients:
Dipotassium Phosphonate 20.40%
Dipotassium Phosphate 22.67%
Other Ingredients 56.93%

Please see the attached scan of all three in the PDF file below.

The point I was trying to make in my original post, was that changing a number by one in a formula even when the names are somewhat similar can have very different properties.

Dutch

Below I have attached a scan of Reliant. It was out in the garage and I didn’t want to go out there last night in the cool. This is the gallon size and the label is easier to read.

Dutch