Cotton Bunchy Top (CBT), a relatively new disease, was first observed by growers in Australian cotton fields in the 1998-99 cotton-growing season. The disease has since been reported across New South Wales and Queensland, from the Macquarie Valley in the south to the Emerald region in the north. CBT is suspected to be spread by the cotton aphid (Aphis gossypii, Glover). Symptoms of CBT include reduced plant height, leaf surface area, petiole length and internodes length. Pale, angular patterns on the leaf margins are often observed with the remainder of the leaf blade usually dark green in colour. These darker leaves have a leathery and sometimes glossy texture when compared to healthy control plants. Typically, the pale angular patches in field-grown cotton turn red as leaves age. Boll development is also affected, with bolls often less than half the size of healthy bolls.