Surfactants are invaluable in a number of agricultural applications in products such as pesticides and herbicides. In these products, surfactants are very often used ill Conjunction with acidifiers in order to improve their half-life. In this paper, we investigate how the change in pH affects surfactant wetting and spreading. We compare the performance of a conventional surfactant, Tritono (R) X-100, with that of a trisiloxane superspreader, Silwet (R) L-77, on a number of polymer coated surfaces exhibiting various degrees of hydrophobicity. Silwet (R) L-77 in water based solutions showed very good wetting capability on all Surfaces. However, its wetting ability was drastically reduced with the addition of acetic acid. On the other hand, Triton (R) X-100 was not affected by the addition of acid and exhibited the same spreading behaviour as in water-based Solutions. (C) 2009 Elsevier Inc. All rights reserved.