Timely update for chill and using rest breaking agents

As the season progresses, Manjimup and Bickley have both accumulated over 70% of the average winter chill threshold.  While Donnybrook is just about there! 

 

The table to the right shows the winter chill accumulation for 2025 season. WA’s production region’s winter chill accumulation is very similar to the low chill units sighted by Dr Nigel Cook. (reference video below). 

Diving deeper into rest breaking strategies used in South Africa

Growing Apples in a Warming Climate: Lessons from South Africa

As climate change continues to reshape growing conditions, apple producers in traditionally cooler regions are facing new challenges. Dr. Nigel Cook, a tree physiologist from South Africa, shared insights at APAL’s Future Orchards® walks in July 2024 on the northern loop, on how growers can adapt to warmer winters and marginal chill conditions.

 The Chill Challenge

In regions like Elgin, South Africa, winter chill accumulation has dropped significantly, sometimes falling short of the 750 chill units needed for optimal budburst. This results in delayed and uneven budburst, leading to trees with fruit, flowers, and dormant buds all at once. The consequences; Poor fruit set, uneven maturity, and reduced yield.

 Rest-Breaking Solutions

To combat inadequate chill, South African growers rely heavily on rest-breaking agents:

  • Hydrogen cyanamide: Doubles bud numbers and improves flowering.

  • Oil mixtures: Enhance budburst but are less effective alone.

  • Hydrogen cyanamide and oil combinations significantly improve budburst and spur development.

  • Cold storage of nursery trees: Simulates natural chill and ensures uniform budburst.

Timing is critical, Hydrogen cyanamide is most effective when applied close to budburst and after a cold front when temperatures begin to rise.

Late Season Growth: A Hidden Risk

Late season vegetative growth can deplete cytokinins, the hormones stored in buds that trigger spring budburst. Managing this growth through summer pruning helps maintain the fruit-to-leaf balance and ensures better dormancy outcomes.

Adapting to Climate Change

Dr. Cook’s message is clear: climate change is real and already impacting apple production. Tools like dormancy breakers, strategic pruning, and tree training are essential for maintaining productivity and fruit quality in warmer conditions.

Growing apples where and when it is too warm | Apple and Pear Australia Limited (APAL)

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