Weather conditions associated with apple production in the Okanagan Valley of British Columbia

An analytical method that generates χ2 indices of association was used to determine the "critical" levels of daily weather occurrences associated with annual variations in apple production (Malus domestica Borkh.) in the Okanagan Valley of British Columbia over a 72-yr period, 1920–1991. The weather was recorded in the centre of the region (the Pacific Agri-Food Research Centre, Summerland). High temperatures during flower bud initiation in June (≥30 °C) and during flower bud development in August (≥26 °C) were associated with poor production the following year. Low temperature during November, December and February (critical value range, ≤ −7 °C to ≤ −29 °C) was the main climatic factor limiting apple production. These time periods correspond to the occurence of historical winter injury events. Daytime temperatures ≥5 °C at times during January also affects apple production adversely, probably because warm weather leads to tree deacclimation. Daily precipitation in March (≥1.0 mm) was associated with goo...