The politicians may still be arguing about climate change, but growers are facing the impacts of increasingly erratic climate daily. At the latest round of Future Orchards® walks, AgFirst consultant Steve Spark shared some practical ideas on how to plan for and mitigate the risks associated with climate change.
Managing climate risks are probably one of the most important management inputs an Australian fruit grower can make, those attending the recent round of Future Orchards walks were told.
AgFirst consultant Steve Spark said living in New Zealand he had not seen managing climate change as a high priority until recent years had brought earthquakes, floods, frosts, unseasonal snow and sunburn.
“I thought New Zealand had a pretty reliable climate,” he said. “We thought we were the most even climate in the world, but that might be changing. Over the last few years we have had a heck of a lot of things happen we have not had to think of before. The climate is getting so much more variable. How do we handle it? The better growers are recognising this and getting on to managing it.”
Steve said that although winter chill decreasing is not so much a New Zealand issue yet, growers around the world were observing delayed and uneven flowering impacting on yield and quality, especially in some parts of Australia.
Breeding programmes were under way to breed cultivars with low chill-requirements, but this would take time.
Meanwhile strategies could include:
- Promote dormancy through the application of defoliants such as Copper Sulphate or other recommended sprays which knock the leaves of to force dormancy
- Use dormancy breaking sprays
- Maintain the optimum nutrition levels
- Grow varieties suitable for lower chill areas
- Grow alternative low chill crops e.g. Avocados.
Steve said forcing early dormancy had to be balanced against allowing the tree to recharge next year’s buds post-harvest.
“One option we are looking at is can we give the trees a month to recharge after harvest, then wait for 10 per cent senescence and then knock the leaves off, using the right product of course,” he said. “We have had a few disasters in earlier years and sometimes, if applying defoliant sprays too early before senescence has started, leaf fall is not always reliable.”
Frost bud susceptibility depends on the development stage and can vary between varieties. While -7.5°C might be the critical temperature for a 10 per cent kill at green tip stage, the same level of damage may be triggered post bloom at just -2.0 °C.
Regional or seasonal differences could also influence the impact with a sudden frost following mild/warmer days potentially destroying all buds, where it would not do so where weather had been cold preceding the frost.
Forewarned is forearmed when it comes to frost, Steve said, and the best management tool was a good weather forecast.
“The cheapest and the best is a good forecast,” he said. “If you know what is coming you can go and prepare, mow between rows, check your sprinklers, prepare a clean herbicide strip.
“You can protect with Low Biuret urea spray before a forecast event and that might help by one to one and a half degrees which might be all that is needed. You can also foliar apply urea in autumn to assist building up better basal leaves.”
- Clean short grass sward – Mowing regularly to keep a short grass sward and maintaining a clean weed-free herbicide strip would help soil heat radiate back to trees.
- Wind machine/helicopters
- Overhead or under tree sprinklers
- Moist soil
- Allow cold air to drain from the orchard by lifting curtains or maintain holes in shelter belts
- Care and timing with dormancy breakers
- Protectant sprays such as Low Biuret urea
- Early basal spur leaf development from good Autumn nutrition.
Where once hail might have been rice-sized in New Zealand, Steve said recent hail events had been more commonly marble, pea or golf ball-sized.
“Things have become more and more extreme,” he said.
While netting was the only feasible protection it was important to ensure structures were strong and would not fail, citing an example where a failed netting structure had left an orchard so badly damaged it had taken five years to recover from.
“A hail storm without protection wipes you out for a year,” he said. “But you could put all that effort in and if it fails you may be worse off.”
Wisely chosen netting could provide protection against extreme climate while also increasing packouts, vigour and soil moisture.
There are many designs, colours and benefits, Steve said, but if chosen wisely, netting could decrease damage from hail and sunburn, wind, birds and flying foxes. However he cautioned it could also decrease pollination (Future Orchards trials are underway in Pemberton on pollination under nets).
January was the hottest on record for most parts of Australia and sunburn is an increasingly widespread issue.
“We are seeing more and more days above 35 degrees in my patch,“ Steve said. “The Goulburn Valley is getting quite extreme. As it gets too hot, the tree shut down.”
Other heat-induced quality symptoms included bitter pit, water core, scald, poor foreground colour and advanced background colour and lenticel breakdown. It can also increase the risk of Biennial bearing.
Strategies for minimising heat stress include:
- Planting crops or varieties tolerant of microclimate
- Use rootstocks suited to microclimate
- Overhead netting can lower the temperature of fruit
- Growing structures
- Good nutritional balance
- Good soil and foliar calcium program
- Evaporative cooling (overhead and under tree)
- Sunburn protectants
- Healthy trees with large active root systems
- Excellent soil moisture management
- Long grass swards (the opposite of the short swards used for frost protection in spring)
- Good biennial bearing management
- Fruit colour enhancements
- Fruit maturation retardants (ReTain, Harvista)
- Harvest at optimum maturity
- Appropriate storage regime
Several Australian states also had their driest January on record and drought and water competition are a key climate risk.
Despite the threat to water security, Steve said many growers did not know their orchard water requirements and these could range by more than 100 per cent, with some using 6 megalitres/ hectare (ML/ha) and others as much as 14ML/ha.
“It is important to know your current and future water requirements,” Steve said.
He said once water requirements were understood growers could assess if they had access to additional water to match planted area or would need to limit planted area to match available water.
Storage wastage should be minimised and overhead netting used for hail or sunburn protection would also improve water use efficiency through reduced water usage.
Water use efficiencies could be increased by:
- Drip not spray irrigation, applied at night not during the day
- Good organic matter and mulching
- Encourage deep rooting
- Match rootstocks and scion varieties.
- Appropriate irrigation design
Steve said the key thing was to have a good weather forecast and to make sure orchards were managed to minimise the impact of changing climate.
“Sitting back and doing nothing doesn’t help us,” he said.
“We’ve learnt that.”
Climate modification and risk management is the first section in the Future Orchards archive library on the APAL website under Industry Info.
APAL’s Future Orchards® program is funded by Hort Innovation using the apple and pear R&D levy and funds from the Australian Government, and is delivered in partnership with AgFirst.