Background
Following the discovery in the early 80’s of the effectiveness of trunk injected buffered phosphorous acid by Darvas and fellow researchers at Westfalia Farms in South Africa, numerous countries around the world have had access to this very cost effective material for the control of various forms of phytophthora in numerous crop and tree species.
In many places it has become common and acceptable practice for farmers to “brew”their own solution, thereby greatly reducing costs.
Legality Warning
Before considering making and injecting potassium phosphonate growers should check their local horticultural regulations as to the legality of doing so.
Safety Warning
The manufacture of potassium phosphonate can involve a strong chemical reaction, the generation of heat, and discharge of gases and should not be attempted inside a closed room, preferably in a covered open sided location. Safety clothing should be worn, completely covering body, head, arms, legs and hands. Safety glasses should be worn along with a safety helmet fitted with full face impervious transparent screen.
Any contact with the chemical should be washed off immediately, eye contact should also be followed up by medical assistance.
Equipment and Base Chemical Required
The following are some items of equipment, chemical and suppliers that may be of interest to people mixing their own material. Inclusion is not a recommendation.
The best mixing drums to use are of stainless steel, such as recycled beer kegs, due to the heat generated and the risk of melting plastic drums should never be used. To aid cooling the stainless steel drum can be placed inside a larger plastic drum and the gap in between the drums filled with water.
MIXING INSTRUCTIONS *** Read Safety Warning First
Note
Both phosphorous acid and potassium hydroxide are hydrascopic, that is they will both absorb water from the atmosphere. They should both be stored in a cool dry place. Bags, etc. should be resealed as tightly as possible, once container has been opened.
Warnings
1 Always add chemical to water, never the other way around.
2 Distilled water should be used.
3 Add chemicals in small amounts stirring gently in between.
4 Large amounts of heat are generated when potassium hydroxide is added, allow to cool once temperature of solution rises above 60C or 140F.
Example – Preparation of 25 Litres of 40% Concentrate pH 7.2
1 Measure accurately 10 kg. each of phosphorous acid and potassium hydroxide.
2 Place 25 litres of distilled water in a stainless steel drum.
3 Add all of the phosphorous acid flake to the water and stir until fully dissolved.
4 Slowly, no more than half a cup full at a time, sprinkle the potassium hydroxide into the mix. Heat will be generated and the solution will boil if too much hydroxide is added too quickly. Continue adding potassium hydroxide until 1/3 is added or temperature rises above 55C, allow to cool.
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