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Foam is widely used for bout marking when spraying broad acre crops. The volume of foam produced, and its persistence, is often variable. Both factors are influenced by the generator and foamer, therefore to evaluate changes to the foam generator it is necessary to identify the key factors attributable to each. Some of the reasons for the variations in foam volume have been published elsewhere (Combellack 1995). However also of concern was the variability in foam life since the coefficient of variation (C.V.) for blob persistence was often in excess of 25% on natural surfaces. This made it very difficult to identify whether changes were due to generator design, the foamer or the surface. To overcome this problem a project was initiated to identify the key factors that influence foam life. A series of tests were carried out to assess the relative merits of two artificial surfaces, a green woven polypropylene 70% shade cloth and an artificial turf in comparison with grassed and cultivated ground. The results show that the variability in foam life can be reduced to a C.V. typically <10% if foam blobs are placed on shade cloth. The results also show that the main determinant of foam life is surface temperature and that foam persistence is negatively correlated with surface temperature. It is suggested that these findings be used as a basis for a protocol to test for foam life of foamers.
foam, bout marking, foamers, foam generation, foam life, foam testing
Principal, Spray Smart Enterprises, Box Hill, Victoria