Russell Fox from Insense Pty Ltd., is using the Horticulture Innovation Fund to trial calcium carbonate spray at leaf fall to increase winter chill accumulation in cherry, apple and almond trees.

By applying calcium carbonate to the trees after leaf fall, the project aims to determine if calcium carbonate will act in a similar way as it does during summer heat periods by dissipating heat by reflectance from fruit surfaces. If heat is dissipated and the tree and fruit buds actually kept cooler, then more chill should be accumulated during the dormant period. The result will be determined by measuring fruit and leaf bud phenology (dates of bud swell, bud burst, flowering and length of flowering period) during the spring compared to untreated trees.

Trialling calcium carbonate at leaf fall

Climate change is a serious concern to deciduous fruit and nut crops in Australia. A fundamental component of these deciduous fruit trees to enable normal fruit bud development, flowering and fruit set, is for the tree to accumulate sufficient chill during their dormant phase, and then heat accumulation at the end of the dormant period and start of the spring growth period.

This chill and heat accumulation is the result of the general climate and also the microclimate within the orchard. Actual requirements for the amount of chill and the amount of heat are being determined, but are not well understood. Actual requirements and timing of each component is specific to crop type and variety. Other factors to consider are also when does dormancy (or chill accumulation) actually begin and when is the heat component required to give an economic and sustainable fruit set and crop yield. Climate change has often been portrayed as a long term management problem. From a fruit and nut growers perspective, 20 and 50 year projections of temperature change are meaningless and beyond current management decisions. However, the effects of climate extremes manifest themselves in each season with different climatic factors that
challenges orchard management and crop viability within each season. Very cool periods affect fruit set and crop growth and very hot periods result in heat stress that affects crop growth and can result in severe damage. The challenge in fruit and nut production is how to manage these extremes as a seasonal event.