Calcium carbonate as a sun screen and drought stress protectant
Increased frequency and severity of heat waves and drought are becoming a major challenge for Okanagan fruit growers. These events can reduce fruit quality and compromise tree health, and may be an important trigger for sudden apple decline. A toolbox to help fruit growers mitigate the impacts of heat- and drought-related stress on fruit quality and tree health is urgently needed. Sprayable nanoparticle calcium carbonate is a potential tool for protecting fruit from sunburn and mitigating water stress, and is less expensive than shade cloth and/or evaporative cooling. This tool was tested on an experimental apple block at the Summerland Research and Development Centre over the summer of 2021. An initial spray was applied to test trees in early June, with a second spray applied immediately prior to the ‘heat dome’ event in late June, and a third spray in late July. Throughout the growing season, stem water potential, leaf transpiration and photosynthesis rates were monitored. At harvest, yield and fruit quality were assessed (e.g., sun burn [Schrader-McPherson scale], fruit size and weight, titratable acidity, and Brix. The calcium carbonate spray reduced the incidence of severe sun burn, but caused no other significant differences in fruit quality. When drought stress was applied, by temporarily cutting off the irrigation supply to both treatments, sprayed trees showed lower water stress than un-sprayed trees. Although just a preliminary study, this work suggests that sprayable protectants, such as nanoparticle calcium carbonate sprays, have potential for protecting fruit quality and mitigating drought stress during extreme heat or drought and may be an important, low-cost tool to include in Okanagan fruit growers’ climate change toolbox.