Damages caused by winter frosts, their temporal variation and frequencies in the main fruit growing region of Transdanubia and of the East Tisza regions of Hungary

Winter frosts are the most important of risks fruit growing, therefore, its quantifi cation is an important task. The measure of the damage is studied by the knowledge of physiological processes. During the physiological rest period, the trees are able to withstand –20 °C frosts without damage, whereas after the rest period, the compulsory (temperature caused) dormancy, a –15 °C frost may cause near 100% frost damage (Proebsting, E. L. & Mills, H. H., 1966). Based upon earlier results, we elaborated the LT50 function for apricot and peach varieties, and distinguished between three categories, as frost susceptible, medium toleerat and frost tolerant varieties. By means of the LT50 function, we may extend the study for all fruit varieties grown in Hungary. Apricots and peaches being the most threatened fruit species of Hungary, we present an example for the use of the function. Two Transdanubian and other two Trans-Tisza growing sites have been selected for the meteorological study, how we could calculate the probability of the damage at least on the 50% level. As by knowing the frequency of climatic risks would help to determine the risks of production. The growing sites and varieties of peach and apricot plantations have been thoroughly elaborated by Timon (2000), Zayan (1981) and Szalay (2001). Our earlier studies stated that the variety Venus known to be extremely frost susceptible suffered heavy damages during the winter in the regions Szeged–Szatymaz at the Lake Balaton at the middle of January (probability 20–22%), whereas at in the region Mecsekalja, the major frost damage occurred at a probability of 13–14% at the end of January (Lakatos et al., 2005a). With the exception of Mecsekalja, the highest probability of winter frost damages is around the middle of January. For a frost tolerant peach variety, Redhaven, the critical period Damages caused by winter frosts, their temporal variation and frequencies in the main fruit growing region of Transdanubia and of the East Tisza regions of Hungary