Blueberry acreage in Florida and Georgia has more than doubled since 2000. In 2016, blueberries were harvested from 4700 acres in Florida and 16,900 acres in Georgia. The two states accounted for 23.3% of the total U.S. blueberry harvested area (U.S. Department of Agriculture, 2017). Despite early-ripening varieties being susceptible to spring frost injury (Strik and Yarborough, 2005), low-chill, early harvest southern highbush blueberries [SHB (Vaccinium corymbosum interspecific hybrids)] have been extensively planted in this region to take advantage of pricing for entrance into early U.S. market windows (Brazelton, 2015; England, 2015). SHB varieties begin to flower in January in both Florida and Georgia, with frost events occurring from January until April. Depending on the floral bud development stage and when temperatures drop to freezing or below, damage can be significant (Warmund et al., 2008). As a result, frost-protection measures commonly are used to mitigate crop loss in Florida and Georgia (England, 2015; NeSmith, 2008).
Cost of orchard establishment can be $10,000 to $12,000 per acre or more (Fonsah et al., 2013; Singerman et al., 2016). Most growers use low-volume (usually drip) irrigation systems to address crop water requirements and overhead irrigation for frost protection. Frost protection, primarily overhead irrigation systems, can add another $2300 per acre to establishment costs (Singerman et al., 2016). Once established, operating costs for frost protection through overhead irrigation can be low (as compared with wind machines and heaters) (Poling, 2008). With relatively low operating costs, the main barrier for the use of frost protection is its limited effectiveness. In general, when temperature drops to –7 °C or wind speed increases to 16 km·h−1 or above, frost protection may not be effective. Other matters that growers should consider in frost-protecting their crops include increased evaporative cooling due to wind, the potential for poor ice formation, ice accumulation breaking and stripping flowers from the plant, and water restrictions due to regulatory requirements or physical limitations of the irrigation system (Perry, 1998; Poling, 2008; Snyder and Melo-Abreu, 2005).
Given these constraints, growers initiate frost protection in advance of a frost or freeze event when the temperature is anticipated to reach critical levels where lethal damage to reproductive tissue can occur (critical bud temperature values). Figure 1 illustrates the established critical temperatures for different blueberry bud stages (Patten et al., 1991; Spiers, 1978). Another problematic constraint is the information gaps related to variety, climate, and bud stage in recommendations provided to growers in Florida and Georgia. As a result, growers in Florida and Georgia must rely on critical bud temperature information developed for other regions.
Overall, the decision to start frost protection at a particular time depends on the cost, information available, and risk attitude of growers to adjust their practices in response to frost forecasts (Crane et al., 2010; Hu et al., 2006; Klockow et al., 2010; Kusunose and Mahmood, 2016; Mase and Prokopy, 2014; Stewart et al., 1984). The study by Stewart et al. (1984), which focused on frost-protection decisions of fruit growers in central Washington, found multiple on-farm weather resources and strategies available to growers to mitigate frost. Perceptions of the weather forecast quality and applicability of the forecast to growers’ production systems were crucial for the decision to frost-protect fruit crops.
Research shows that more studies examining the determinants of frost-protection decisions are needed, given the potentially high economic impact of frost and the need for more efficient frost-protection systems and opportunities to save water and energy by developing precision frost-protection technologies (Chevalier et al., 2012; Simnitt et al., 2017). The objective of this project was to identify, by survey, the prevalence of frost-protection systems, the use of information resources to mitigate damage caused by frost events, and the decision timing for operating a frost-protection system by Florida and Georgia blueberry growers.
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