The pattern of freezing of grapevine shoots during early bud growth

The pattern of freezing of two varieties of grapevine during spring bud burst was characterised using infrared thermography. All plants studied showed endogenous freezing of the stems and subsequent rapid ice spread (0.47 cm/s) analogous to ice spread in bulk water suggesting ice travel in the xylem. Barriers to ice spread were observed between stembranches and more importantly between the stem and buds. Buds froze after the stem and freezing appeared to be initiated from the stem. The lack of a fully functional xylem system is proposed as the barrier to ice spread. All buds which froze suffered complete frost kill whilst frozen stem recovered unharmed. Only 58% of the buds froze and those that did not freeze survived completely.