Asymmetrical canopy architecture due to prevailing wind direction and row orientation creates an imbalance in irradiance at the fruiting zone of grapevines

Much effort is invested in trellising and training grapevines to maximize radiation interception by the canopy and to manage the radiation environment of the fruit clusters. Slope permitting, conventional wisdom among winegrape growers prompts many to adhere to north-south row orientations to balance between the two sides of the canopy both photosynthetic efficiency and the exposure of fruiting zones to solar radiation. In windy sites, thigmomorphogenesis in annually renewed shoots can reshape a bilaterally balanced canopy. We measured irradiance at the fruiting zone and shoot geometry in two contiguous vineyards differing only in row orientation. The prevailing west-southwest winds were roughly parallel to the rows of one vineyard and at an oblique angle to the rows of the second vineyard. Mean wind velocity in the prevailing direction was 3.3 m s−1 during the growing season. Shoots were grouped into four classes based on row orientation and shoot azimuth from the cordon. Windward shoots were significantly shorter (26-29%) than all other classes of shoots because of fewer nodes per shoot. Mean internode length per shoot (≈5 cm) did not vary between shoot classes and was not related to row orientation. Regardless of row orientation or initial shoot azimuth, shoot tips tended to be displaced eastward (leeward). In rows oriented roughly parallel to the prevailing wind, shoots exhibited distinct down-row streamlining and vines had a bilaterally uniform canopy about the cordon. In rows at an oblique angle to the prevailing wind the vines did not form a uniform canopy about the cordon. Both row orientations resulted in similar differences between sides of the canopy in total irradiance at the fruiting zone (+5.4 MJ m−2 d−1 on the west side of rows oriented at an oblique angle to the wind; +6.0 MJ m−2 d−1 on the south side of rows oriented parallel to the wind); however, the timing of peak intensity on the side receiving higher irradiance differed by row orientation (11.9 LST at south-facing fruit; 13.7 LST at west-facing fruit). Wind-induced canopy asymmetry could result in unequal berry ripening in areas of high irradiance where peak insolation of the berries coincides with the highest temperatures of the day. Results indicate that in consistently windy locations, growers should establish row orientation based both on sun-earth geometry for maximizing radiation interception by the canopy, and on the consequences of radiation distribution at the fruiting zone due to wind-induced canopy asymmetry. In established vineyards, growers could compensate for non-uniform canopy architecture to some extent with modifications to the trellis system and standard training practices.