Physico‐chemical studies on agricultural sprays. VI—Survey of methods for measuring the wetting ability of spray formulations

Several methods have been suggested for the measurement of the wetting efficiency of high‐volume sprays and some of these have been examined to see how far they will predict the wetting ability of a range of wetting agents applied to several leaf surfaces. It is concluded that a satisfactory wetting test must involve the appropriate spray target surface and also take into account the effects of spray droplet impaction; these requirements are satisfied by a test based on the visual assessment of wetting under practical spraying conditions. Of the other tests examined, the measurement of the receding contact angle is of value in recognising the extreme case of complete wetting of a surface and the tape‐sinking test may be used, with anionic and non‐ionic wetters, as a rough guide to the overall efficiency of wetters on leaf surfaces.