The Australian cotton industry has, until recently, relied largely upon residual pre-plant and pre-emergent herbicides for weed control in irrigated production systems. These herbicides provide good protection against a broad spectrum of weeds. In some circumstances, however, residual herbicides adversely impact the growth and development of young cotton seedlings. This is particularly the case when cool wet conditions occur early in the cotton season. As well, the majority of these herbicides have a half-life of three to four months and may persist for long periods when bound to clay particles within the soil profile. Movement of these molecules bound to clay particles is common in irrigated systems. While procedures to minimise riverine contamination are in place on irrigated farming systems, herbicides are routinely detected in the river systems of the central and north-west regions (Table I). It should be noted that of these detections atrazine and metolachlor are the only herbicides detected in significant amounts and these are used extensively in dryland sorghum.