Assessing Chilling Conditions by Sites and Years for Perennial Fruit Production in Kentucky

Abstract

Temperate regions of the world are characterized by seasonal warm and cool temperature. Cool temperature enables the plant to undergo physiological processes essential for flowering and fruit bearing in the following season. Failure of environments to provide chilling conditions required for the fruit cultivar results in deformed leaves, fruits, or barren trees. The present study was conducted to assess production and distribution of chilling hours in Kentucky environments. Weather data were provided by Kentucky Mesonet system for 50 counties over a 5-year period. A chilling unit is defined as a clock hour in which air temperature is between 0°C and 7.2°C. Temperature readings in this range were recorded from September through April. Average number of chilling hours observed in the study was 1556 overall, and ranged from 1463-1680 for sites, and 1473-1842 for years. Estimated chilling hours were more variable for years than for sites. Consistency of chilling results was high when measured by linear correlation and relative standard deviation statistical procedures. Accumulated chilling hours at the sites reached approximately 1000 by mid-January thereby meeting the requirements for many fruit crops. At that point, plants would be ready for bud break and become subject to freezing damage. The results indicated that chilling exceeded requirements for most Kentucky crops. This margin of excess has both negative and positive value. First, the plants become more vulnerable to freezing damage before winter weather is completed. The higher risk could be mitigated by growing cultivars with longer chilling requirements. Second, since warming has been shown to decrease chilling production, the margin of chilling hours could provide time for adjusting horticultural enterprises in Kentucky to global warming. Additional understanding of relationships between environments and chilling will contribute to perennial fruit production in temperate regions of the world.