Physico‐chemical studies on agricultural sprays. IV. —The retention of spray liquids on leaf surfaces

The retention of spray liquids has been measured on the surface of leaves of various plants. Various spray liquids, having a range of wetting abilities, were used and the retention was measured both by spraying the surface up to the point of spray run‐off, thus giving a measure of the maximum retention, and by spraying the surface to beyond run‐off conditions. For any given surface, the maximum retention was related to the theoretical retention factor, which was calculated from the values of the dynamic advancing and receding contact angles of the spray liquid on the solid surface and from the surface tension of the spray liquid. After spraying beyond run‐off, the theoretical retention factor will predict the relative levels of retention with reasonable accuracy. This agreement between measured and theoretical retention has enabled the retention theory to be used to study the importance of many of the variables that govern spray retention in practice. These variables are discussed.