IT is well known that the theoretical maximum yield potential for winter cereals in Australia is achieved when crops flower mid winter (July-August). But for most parts of the northern grains region, there is a very high probability that crops flowering in July and August will be lost to frost damage. Yield potential drops rapidly after the optimum date at between one to two per cent per day (Figure 1). As we generally recommend planting dates leading to an early September flowering date, the delay past the optimum is at least five weeks and often up to seven or eight weeks. In the northern grains region conflicting climatic influences -including moisture availability and high temperatures - severely constrain the timing of winter cereal flowering and grain filling if yield potential is to be maximised in face of frost risk (Figure 2).
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