Understanding apple and pear production systems in a changing climate (AP12029)

What was it all about?

This project was tasked with reducing the vulnerability of the Australian apple and pear industry to changes in our climate. Its key activities included modelling a changing climate to investigate potential effects on winter chill, tree flowering, fruit sunburn and fruit yield, as well as looking at appropriate adaptive responses for the industry.

In modelling future climate scenarios – both medium and worst-case scenarios for the years 2030 and 2050 – the researchers found:

• Winter chill accumulation is set to decline in each of the country’s pome-fruit-growing regions (the historical data shows that regions with a milder climate have been experiencing a decline in annual winter chill accumulation since the late 1960s, while colder regions have yet to be impacted)
• Warmer locations are expected to experience a reduction in winter chill of more than 20 per cent by the year 2050
• The coldest apple and pear growing regions are expected to experience a winter-chill decline of less than 10 to 14 per cent
• All pome fruit regions can expect to experience an increase in the number of extreme heat days during the growing season, with the greatest impacts likely to be in regions with hot summer climates.

In short, the researchers report that climate change “will add significant variability into the pome fruit production system with respect to flowering and fruit quality”. It is expected that growing regions are likely to experience symptoms of inadequate chilling with increasing frequency in future years, including greater variability in flowering dates between seasons, cultivars and individual trees, and irregular and protracted flowering.

Looking at the Cripps Pink apple cultivar in particular, the research has indicated an earlier full-bloom date can be expected in high-chill locations by 2050, while a later bloom date is expected in milder winter locations by 2030 (with flowering dates delayed by more than a week by 2050).

With an increase in extreme heat days, an increased risk of fruit sunburn is also expected.

The researchers note that while Australian growers are used to dealing with some level of climate variability – and that the effects on flowering and fruit quality may be within the range of grower experience in some regions up to around 2030 – by 2050 growers will be operating outside of current experience.

Key findings included:

• Dormancy-breaking sprays are likely to be a viable tool for managing delayed and variable flowering in some cultivars in lower winter chill years, based on initial trials
• Despite this, planting lower-chill cultivars and, as possible, matching cultivars with climate is the preferred adaption option
• There is a need for detailed information to help growers be able to match apple and pear cultivars with suitable growing climates – including matching cultivar chilling requirements with winter chill, and heat tolerance with summer temperatures.
• Netting will reduce the risk of sunburn damage, with the research showing air-temperature thresholds for fruit under netting were higher than the thresholds for fruit without netting. Project trials in Western Australia found black and white netting to be equally effective in reducing fruit surface temperatures in late summer.
• There is a need for industry to look towards guidelines for managing extreme heat in orchards, including the use of evaporative cooling, stress-reduction chemicals, tree canopy structure and more.

The researchers also recommended:

• Comprehensive in-orchard monitoring of flowering dates across cultivars to provide early indication of cultivars that might be impacted by warmer winters, as well as identification of subtle shifts in the timing of flowering between cultivars and their pollinisers
• In blocks where flowering is becoming increasingly irregular, growers will need to assess the point at which production becomes unprofitable.

ACT NOW

The project produced an interactive chill calculator, to enable growers to calculate winter chill accumulation in their region during dormancy – find it at www.hort-science.shinyapps.io/ChillCalculator.