Sowing a range of cultivars in their ideal sowing windows will give wheat growers the best chance of balancing the increasing risks of heat and frost damage.
Former CSIRO senior research scientist James Hunt says weather conditions in recent years have shown why it is so important to sow a diversified wheat program.
Dr Hunt says planting a range of cultivars at their optimal sowing time can improve profitability for wheat growers.
‘‘We had unprecedented frosts in 2014 and we had very early heat conditions in 2015,’’ he said.
‘‘It is more important than ever to optimise the sowing window so that, as much as possible, all wheat flowers in its ideal window to minimise the risk of frost or heat damage.’’
The direct effects of heat stress are estimated to cost grain growers in south-east Australia almost $600 million per year and about $1.1billion nation-wide.
Frost is estimated to cost south-east Australia at least $100million a year in unfulfilled or lost yield potential.
Due to the effects of climate change, heat stress and frost are likely to play an increasing role in the future and will require growers to take steps to manage the risks.
Growers who plant the majority of their wheat program using a single high-performing cultivar struggle to plant their whole wheat program in a time close to the ideal sowing window.
This can result in flowering occurring earlier or later than desired.
This then leads to a higher heat stress risk if sowing is delayed, or higher frost risk if planting too early.
For example, if the ideal sowing window is considered to be about five days either side of the target date, growers who sow a single cultivar during three weeks will have sown at least half of their crop (11 days out of 21) outside of this window.
By comparison, if the wheat program was split up into two cultivars, almost 100 per cent of the crop can be sown in its ideal window.
Time of sowing
Dr Hunt says it would be impossible to choose a combination of sowing time and cultivars that would prevent exposure to heat and frost risk. However, time of sowing trials in South Australia and Victoria have shown that certain strategies will give crops the best chance.
‘‘Depending on the local climate and duration of the wheat-sowing program, growers can take a few different approaches to optimise time of sowing,’’ Dr Hunt said.
‘‘In many regions of Victoria, growers can start with a winter wheat after a rain in April, then move onto slow-spring wheats and then mid-fast cultivars in May. The different maturity drivers of the cultivars mean that they still flower in the ideal window despite being sown at different times, meaning that overall yield is optimised and risk is minimised.’’
A time-of-sowing trial at Berriwillock in Victoria showed that where there is soil moisture, sowing early can provide higher yields than traditional sowing dates.
Diversity is the key
The best strategy to manage heat and frost risk is diversity. By choosing a range of crops, cultivars with different maturity drivers and optimum sowing dates, growers will have the highest percentage of their program flowering in its ideal window.
‘‘The opportunities to take advantage of early sowing have never been better,’’ Dr Hunt said.
‘‘Previous barriers have been overcome through no-till technologies, summer fallow management and cheaper chemistries to control early pests and diseases.
‘‘Researchers are working on developing new cultivars that are better suited for sowing early, including a new winter wheat for South Australia. But there is no reason most growers can’t spread out their wheat sowing by incorporating a few different cultivars with different maturity drivers.’’
Dr Hunt’s tips for management of early-sown crops:
■ Don’t dry-sow slow-developing cultivars (EGA Wedgetail, Cutlass). They will flower too late if not established early. There needs to be seed-bed moisture and ideally some stored soil water to get them through to winter.
■ If growing winter wheat (EGA Wedgetail) and not grazing, defer nitrogen inputs until after GS30.
■ Pick clean paddocks — winter wheat is not competitive with rye-grass, and common root diseases are exacerbated by early sowing.
■ Protect against diseases associated with early sowing — barley yellow dwarf virus (imidicloprid on seed backed up with in-crop insecticides at the start of tillering if aphid pressure high), Zymoseptoria tritici in some areas (flutriafol on fertiliser and timely foliar epoxiconazole applications at GS30 and GS39). Many slow developing cultivars also have poor resistance to stripe rust (flutriafol on fertiliser and timely foliar fungicide application at GS39).