End of Dormancy Winter Chill Update 2024
This week has been cold and wet and delivering the right conditions required for pome fruits. Autumn started with very warm days and nights; winter chill accumulation was slow to start in 2024. The first chill portions for Bickley and Donnybrook were recorded in late May, with Manjimup slightly earlier in the first week of May. Winter chill accumulation has been slow to start and we are now tracking along well below in the lowest of 10% of years, experiencing a very warm winter for 2024. For most locations, we have just reached the 70% of the average winter chill portions required to break dormancy for 2024.
If you check your records, 2014 was also a year of very low chill and 2013 also had a late start and low chill. Further investigation of previous low chill years can be done using the My Climate View resource My Climate View developed by the Climate Services for Agriculture program funded by the Australian Government’s Future Drought Fund (FDF). As shown in the past and projected winter chill accumulation graph in figure 1, the chill accumulation is set to decline in the future.
Figure 1 Past and projected future chill accumulations for Manjimup
What to expect after a low chill year for Pome fruit? When we were monitoring flowering in the climate change project (2014-1016) green tip started earlier and the time between first flowers and full bloom was extended. This was consistent with the research findings that when chilling requirements are not met during dormancy there is a risk that there will be light and variable flowering with a protracted flowering period, poor fruit set, distorted fruit, delayed foliation and extended blooms.
“In the next couple of weeks, it will be time to start considering the use of dormancy breakers to compact flowering and ensure more uniform fruit maturity. Consider the purpose of the application to set back or induce early bud break and then waiting for the right weather conditions to apply. As always ensure you follow the label directions.”
Dynamic chill model (Erez et al. 1990) is the current best practice model, especially in warmer climates. It calculates chill in Chill Portions, based on hourly temperatures. The Dynamic model has many features that capture known temperature-winter chill relationships that are lacking in other models including the Chill Hours model. In the graphs below the shaded area represents the highest 10% of years through to the lowest 10% of year. Solid blue line is this year’s winter chill accumulation. The follow the link below to calculate todays winter chill accumulation, for your location using the bureau of meteorology weather stations. https://www.daf.qld.gov.au/news-media/campaigns/agtech/about/types
