Influence of weather on apricot, peach and sweet cherry production in the Okanagan Valley of British Columbia

An iterative chi(2) method that generates indices of association was used to determine daily weather occurrences associated with annual variations in peach (Prunus persica Batch.), apricot (Prunus armeniaca L.), and sweet cherry production (Prunus avium L.) in the Okanagan Valley of British Columbia over a 72 yr period, 1920-1991. During September and early October of the pre-harvest year, warm daytime temperatures favoured apricot (>= 26 degrees C) and sweet cherry production (>= 19 degrees C), probably because this promoted flower bud development. High daytime temperatures (>= 27 degrees C) were detrimental to apricot production in August of the pre-harvest year. During the pre-harvest year, peach production was only weakly associated with daytime temperature. Precipitation adversely affected peach and sweet cherry production in the pre-harvest year indirectly by associated lower temperatures or directly by enhanced disease infection. The main climatic factor limiting production of these crops was low temperatures from November to February (critical value range, >= -13 to >= -24 degrees C, nighttime temperature) that cause winter injury. Precipitation during this period, usually snowfall, mostly favoured production. Poor production years were also associated with low nighttime temperatures (<= -2 to -5 degrees C) in spring at the time the flowers are prone to frost injury. During the bloom period warm temperatures (>= 16 degrees C, daytime temperature) favoured Prunus production, probably because of the temperature requirements for good pollination and flower set. Rainfall during fruit development and harvest of sweet cherry reduced production because of rain-induced cracking. Daytime temperatures were detrimental to production of apricot (>= 31 degrees C) and sweet cherry (>= 33 degrees C to >= 37 degrees C) during harvest. The anticipated climate change appears to favour Prunus production in the Okanagan Valley, except for increased rainfall on sweet cherry production.