BollgardII accumulated yield faster than conventional cotton due to higher retention combined with a very low proportion of tipped plants. This meant that late in flowering and at cut-out BollgardII was less able to compensate for water stress equal to a depletion of =120mm of soil water (= 58% plant available soil water) and yields were lower relative to conventional cotton stressed at the same time., *Yields and soil water extraction of BollgardII and conventional cotton were the same when moisture stress occurred at early flowering., *With full irrigation, that is soil water deficits of 44 to 83 mm, BollgardII had the same yield or higher yield than conventional cotton but matured earlier due to more rapid boll setting., *Future research will aim to optimise irrigation scheduling of BollgardII for yield and water use efficiency