Modelling apple tree bud burst time and frost risk in Iran

The bud burst phase of orchard trees is the most critical phase in relation to low temperature and frost since the most parts of the bud, especially the ovary, are very sensitive to low temperatures. Therefore, predicting the time of bud burst is important. If a model can predict the time of budding, it would be possible to protect buds from late spring frosts. In this study, the budding time of apple trees at two agrometeorological stations in northeast and northwest Iran was predicted by using a chilling and forcing model. Data for years 2002–2006 were used to calibrate the bud burst prediction model and respective information for the years 2007 and 2008 was used to validate it. For this purpose, five threshold temperatures (TC) and 11 chill requirements (CR) were used. Among 55 combinations of TC and CR, the combination with minimum Root Mean Square Error (RMSE) was selected for predicting bud burst of apple for each region. Meanwhile, the probability of last date of frost in spring was estimated by statistical distribution. By comparing the probability of frost occurrence with the date of predicted bud burst, the risk of frost damage on apple budding was estimated. Copyright © 2009 Royal Meteorological Society