A widespread problem of premature defoliation and physiological cut out of cotton has occurred in the Emerald Irrigation Area since the early 1980s. The problem was particularly severe in 1988 and 1989. This premature senescence has consistently been associated with a discolouration of the upper leaves towards plant maturity, and also with the leaf spot fungus Altemaria macrospora. Premature senescence can occur and lead to leaf loss even in the absence of leaf spot infection, although defoliation is neither as swift or complete. To enable comparison between visual estimates in the field, a standard scale of the symptom severity has been adopted (table 1). This is usually assessed at a time just prior to the first boll splitting.