Occurrence of Winter-kill to Apple Trees in the Okanagan Valley of British Columbia and Its Relation to Autumn and Winter Temperatures

in HortScience
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  • 1 Research Centre, Agriculture and Agri-Food Canada, Summerland, B.C. V0H 1Z0, Canada

Winter freeze events, identified by horticulturists to lower yields or kill trees (estimates vary by year from 1000 to >200,000 trees), have occurred in the Okanagan Valley of British Columbia 18 times in 94 years (1 in 5 years). To determine the association of winter temperatures and production, 72 years (1920–91) were separated into quartiles by level of production. Then, a maximum χ2 value was produced by a scanning iterative technique comparing each of the extreme quartiles with the combined mid-quartiles. A strong association was found between level of production and the low minimum temperatures in November, December, and February but not January. This result agrees with the historical records that indicate three winter-kill events occurred in November, five in December, one in January, and three in February during the same time period. Warm temperatures in September were associated with low production, indicating the possibility that warm temperatures at this time delay acclimation. Warm temperatures in January also were associated with low production, indicating a possible effect in hastening deacclimation.

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