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Buffers and Acidifiers

In general, many products used to control pests and diseases are more stable in solutions that are slightly acidic to neutral, between pH 5 and pH 7:

  • Buffers stabilise pH and tend to maintain this level even if conditions such as water alkalinity change.
  • Acidifiers neutralise alkaline solutions and lower pH but do not have a buffering action.

Some agrichemical products susceptible to alkaline hydrolysis may have a buffer already incorporated into their formulations.

Some water used for diluting agrichemical formulations is alkaline (high pH). If the pH is sufficiently high and the agrichemical is subject to degradation by alkaline hydrolysis, it may be necessary to lower the pH of the mix water. If the agrichemical is alkaline labile but poorly water soluble, the formulation colloids will provide some protection from hydrolysis in the spray. However, to the extent that hydrolysis occurs from the dried salts in the residues on the leaf, the formulation will not provide protection.

Buffers contain phosphoric acid or a salt of phosphoric acid, which will lower the pH or acidity of the water and tend to stabilize the pH at an acceptable value. The efficacy of any buffer product depends on its concentration of phosphoric acid and the degree of alkalinity or 'hardness' of the mixing water that is being neutralized. The more alkaline the water, the greater the amount of buffer that will be required. Some products give directions indicating the amounts of buffering agent to be used with water of different alkalinity, but not all do.

Some buffers have sufficient surfactant present to also perform as wetter-spreaders. The concentration of surfactant and phosphoric acid are usually lumped together and it is not possible to determine the concentration of either and thus predict their efficacy. It appears that for some buffers the surfactant concentration is 50% or more, though some do not contain surfactants, and that the phosphoric acid concentration ranges from about 2 to 10%. Some foliar nutrients that contain phosphorous are also labelled as buffers because the phosphorous nutrient is present as phosphoric acid or a salt and thus can also act as a buffering agent.

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