The application of cotton defoliants has on occasions been observed to effect the growth of native trees. Cotton growers need to know the potential effects of the defoliants on native trees in their local environment. They also need to know the implications of defoliant drift onto their spray drift buffer strips, which growers have spent many hours and dollars establishing on their farms. Spray drift from cotton defoliant chemicals has also been suggested as a potential causal agent of native tree dieback in the Liverpool Plains region of NSW and greater north-west NSW. Native tree dieback can be caused by many factors and the causal agents have not been effectively identified or justified, although many hypotheses have been formulated. Such causal theories include insect and bird attack, root pathogens such as Phytophthora cinnamomi, mistletoes, poor seedling recruitment, dryland salinity, grazing, old age, drought and waterlogging. The primary aim of this study was to determine whether cotton defoliants affect native tree species common to north-west NSW and to quantify any impacts.