Mechanical Winter Injury in Grapevine Trunks

Abstract

Trunk samples of Gewürztraminer, Chardonnay, Concord, and Riparia were collected during the 1978 winter season from vineyards of the Niagara Peninsula in Ontario and analyzed for surface resistance to water uptake, moisture transfer and content in the xylem and phloem and for mechanical freezing damage in phloem and phellem. Staining methods were used to evaluate surface resistance and moisture migration. Freezing experiments were performed in an electronically controlled freezing chamber capable of simulating winter conditions in Ontario vineyards. The experiments showed that the late maturing Gewürztraminer cannot maintain its content of freezable water below critical levels during thawing periods due to inferior wood maturity with little suberin protection. Excessive ice formation in subsequent freezing periods will cause mechanical ruptures in cell and vessel walls of the phloem as well as in the phellem epidermis. Mechanical freezing injury is proportional to the concentration of freezable water and the temperature drop below the supercooling point of the tissue fluid.