Any water-based formulation that contains some type of surfactant (such as an pesticide) and is subject to air entrainment (such as during the mixing process) will usually exhibit some degree of unwanted foam.
Foam is difficult to break down because it is stabilised by the surface elasticity and surface viscosity of its film. Silicone-based anti-foamers and de-foamers such as Foam-Fighter have low surface and interfacial tensions. This enables them to flow easily over the film where they interfere with the foam’s properties.
Due to their low surface tension and interfacial properties which when combined with their ability to disrupt the film that supports surface foam silicone-based anti-foamers causes the foam wall to thin and collapse.