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GRAPEGROWING does not stimulate renewed shoot growth. However, overhead irrigation must be used with caution, as it can cause and exacerbate Botrytis bunch rot and/or berry cracking. PWV Bibliography 1. Keller, M. The science of grapevines: anatomy and physiology. 2010 Burlington, Elsevier Academic Press. 2. Matthews, M.A., G. Cheng, S.A. Weinbaum. 1987 "Changes in water potential and dermal extensibility during grape berry development." J. of Am. Society of Horticulture Science 112: 314-319. 3. Becker, T. and M. Knoche. 2011 "Water movement through the surfaces of the grape berry and its stem." Am. J. of Enol. & Vit. 62: 340-350. 4. Biondi, M. Dynamics of grape berry volume change during ripening. 2007 M.S. Thesis. Washington State University. This research was supported by funds from the USDA Northwest Center for Small Fruits Research, the Chateau Ste. Michelle Distinguished Professorship and the Rhone Rangers. We thank John Ferguson for skilled technical assistance. Figure 4. A root pressure chamber was used to stop xylem backflow by pressurizing the roots of potted grapevines. What is worse is that water can move into a berry through the skin.3,4 Thus, the berry water balance is tilted toward increased cracking incidence. Berry cracking was observed when we artificially increased the humidity around the clusters by bagging them. Also, individual berries took up water (up to 9% of berry weight) when they were immersed in water even with sealed pedicels.4 As ripening progresses, berries naturally receive less water from the xylem. This means that water derived from the soil will not "dilute" berry quality late in the season. However, overhead irrigation and rainfall may cause more water to be retained in the berries and even more water to be taken up directly through the skin or stem surface, causing berries to crack. Cracked berries may lose a tremendous amount of sugars with continuous rainfall. We have found that berry total soluble solids dropped as much as 15° Brix due to sugar leaching after cracking.4 Therefore, when using drip irrigation, there should be no fear of applying irrigation late in the season so long as it pr actica l win ery & vin e ya rd JU LY 20 13 67