S11 - Session P4 - Fruitset stabilisation in frost situations - pip an stone fruits

Authors: Michael Zoth *

Climate change effects influence fruit production a lot. At least in central Europe the fruit bearing trees are flowering earlier in springtime and the risk for severe frost damage or cold stress injuries increased during the last 20 years. In case of frost the orchards will be protected with frost irrigation if enough water is available in sufficient quantity. Without the use of water the farmers try to establish useful und less expensive heating 'procedures', such as wax-candles, wood-pellet heaters, gas heating devices or they use wind machines like permanently installed or mobile frost fans. Next to this the use of commercial products containing phytohormones might help to lower frost losses and stabilise fruitset and cropload. Over several years with diverse intensive frost periods and frost injuries on flowering organs, the use of PGR's like prohexadione-calcium products with additional 6-benzyladenine and gibberelic-acids GA4/GA7 products were investigated on apple and sweet cherry cultivars. The lower the natural fruitset after the frostperods was, the better the combination of PGR's worked and increased the fruitset. Some comercial products, registered for oecological fruit production, showed a scant positive effect in fruitset stabilisation when used in apple and pear production.