Mist Cooling to Delay Bloom and Prevent Frost Damage—Old Idea, New Technology

Recent shifts in temperature and seasonality have significantly impacted commercial fruit production in the Great Lakes region. Michigan's tart cherry and apple production in 2012 was reduced by about 90 % and 88 % respectively compared to the previous year’s production due to a series of spring freeze events that followed an abnormally warm temperature in March. Bud development is driven by the localized accumulation of heat units once endo-dormancy has been satisfied. Evaporative cooling with water prior to the onset of growth has been used in the past (mid 70’s and early 80’s) to delay early development of flowers; one to three week delay was observed. However, related problems (more disease, poor fruit set, and large applications of water) reduced its potential for commercial use. This study re-examines mist-cooling to delay bloom by bringing together three new or refined technologies: application of water by mist via new pesticide application system called solid set canopy delivery system (SSCD), modern weather sensing and control systems, and evaporative cooling application based on changes in temperature and humidity. The study aims to identify the timing and discharge rate of mist applications necessary to delay early vegetative stages by suppressing the temperature of cherry and apple buds. In 2013, SSCD system was set up at three different locations in Michigan on sweet cherries, and apples to test the feasibility of the system. The study consisted of three different treatments: no misting, misting from the first week in April until first flower (May 7), and misting from the first week in April through full bloom (May 15). Misting delayed the bloom by 7-10 days in both cherry and apples depending on the variety and treatment compared with the control. The total rate of mist application was of 11-14 cm/ha, which is 75% less than application rates reported in previous studies. No significant difference was seen in fruit set, disease, size, color, firmness and sweetness among the treatments. This approach is expected to directly increase the economic viability and sustainability of the region’s fruit industry by reducing the vulnerability of freeze damage.