California cotton growers experience some problems in the late-season period which have so far defied a good description in terms of causes. Referred to as “foliar decline,” “late-season collapse” or “foliar bronzing,” symptoms are varied and can be as minor as reddening of the upper plant foliage to complete leaf loss and cessation of terminal meristem growth. Early onset can impact developing bolls, fiber quality and yield in both California Acala (Gossypium hirsutum L.) and Pima (G. barbadense L.). Soil and plant tissue samples were collected from over 65 fields showing plant symptoms corresponding with late-season foliar decline since 1997. Potassium deficiency has been implicated in some but not all of these fields. Low levels of tissue N, P and Zn were also measured. Soil test K and P levels ranged from borderline deficient to sufficient. Application of soil applied K (225 or 440 kg K₂O ha^-1) at seven Kern County Acala and Pima fields have been inconsistent in alleviating “late-season decline” symptoms. There does not appear to be any specific cure for this problem. Data on fruit load leaf weight or leaf area ratios suggests that where problems have been seen with early leaf loss and leaf “bronzing,” growers should monitor plant vigor relative to developing boll load. Growth regulator application may amplify potential problems whereas timely foliar or water run fertilizer applications may reduce the problem. While varietal differences have been observed in the development of leaf symptoms, varieties that remain “green” and avoid “late-season decline” have also been low yielding. Field conditions producing root damage or limits to root system development can produce earlier and more severe “leaf decline” symptoms.