Spring frost effects on 30 sweet cherries varieties grown in North Italy

In the Piacenza district, the cherry cultivation was made in a traditional way with big dimension trees and crowns over 3–4 meters from the ground. In the last 20 years, the cultivation was renewed with the introduction of new varieties and the generalized use of “palmetta” training system, the latter in order to facilitate cultural practices, especially fruit harvesting, because the bearing branches are near to the ground. In the cherry growing area of Piacenza district, in the last 25 years of 20th century, the plants are “Italian palmetta” trained to facilitate the cultural practices especially harvest. The occurrence of the spring frost during sweet cherry flowering in this area, gave our Institute the opportunity to check the effect of this spring frost. These events happened in 1995 (Roversi, Ughini, 1995), in 2002 (Roversi, Rossi, 2003 a) and 2003 (Roversi, Rossi, 2003 b). All these researches have been made directly in field conditions where, of course, the situation of plant age, rootstocks, soil management, kind of bearing branch and genotypes were very far from an ideal experimental field in which all these variables could be under control. However, in general, the results of these researches clearly demonstrate how the “Italian palmetta” training system can be dangerous. In fact, in the last 45 years, in the considered area, the spring frost occurred one time every 2/3 year. Again the spring frost damages involve especially the flowers in the lower part of the canopy and are related to flowers opening phase. In the last 10–15 years, some sweet cherry growers of the Piacenza district used to insure their orchard against climatic adversity likewinter and spring frost, and hail. Unfortunately, the insurance companies aswell as the growers don’t well know the sensitivity of different sweet cherry varieties to these adversities. In 2008, a severe spring frost occurred and this has given us the opportunity to supply growers and insurance companies with new information about the varieties sensibility to frost and to confirm our previous results or not.