Flowering of hazelnut cultivars and how it relates to temperature in southern Ontario

Hazelnuts (Corylus avellana) are monoecious, wind-pollinated, and self-incompatible, which guarantees cross-pollination and genetic diversity. Also, they are dichogamous, and in many locations male flowers open earlier than female flowers. Pollination starts with catkin elongation, differentiation of anthers, and release of pollen, which spreads with wind. Flowering can happen in late fall through early spring based on the location, genotype and climate. In southern Ontario flowering starts late February based on the weather conditions. Typically, female flowers become receptive before catkins release pollen and stay receptive for up to two months if they do not receive compatible pollen. We recorded flowering time and stages of flowering in our variety trial in 2011, 2012, 2013, and 2016 at the Simcoe Research Station in Southern Ontario, Canada. While female flowers became receptive from early February in some years, the shed of pollen spanned around 2-3 weeks, usually in March. A severe frost during February and/or March can damage the catkins, interrupt pollination, and potentially decrease nut yield. We have collected temperature data from the weather station, calculated growing degree days (base 2°C) and correlated it to flowering stages. The goal of our research is to predict flowering and pollination time based on the growing degree days. This will help us to predict possible catkin freezing events, and help us to use production practices that can ensure adequate pollination, such as, protecting catkins from the frost or improving the efficacy of artificial or supplementary pollination.