Issue link: http://read.dmtmag.com/i/333548
3 8 V I N E YA R D & W I N E RY M A N A G E M E N T | J u l y - A u g 2 014 w w w. v w m m e d i a . c o m Since post-veraison grapes are the most susceptible to heat dam- age, rows should be oriented to shade clusters during the hottest part of the day at that time of the growing season. For North Coast California vineyards, for example, post-veraison berries and the hot- test, longest days usually coincide in August and September. By evalu- ating the solar position at your site at the hottest time of the day dur- ing this time of year, and by taking into consideration site slope and aspect, you can determine the row orientation best suited to protect your grapes. There are apps available, such as SunCalc, which provide the sun trajectory throughout the year at any given location. The solar angle around solar noon, or just before the hottest part of the day during the hottest months of the year, is the same angle that vineyards should be planted to reduce direct sun on the clusters. In most North- tion versus absorption due to berry color. However, various studies have also shown that grape berry transpiration, a natural cooling mechanism, declines during berry development and is reduced post- veraison in berries of all colors. After veraison, berries have few active stomata and do not transpire as much to remove heat. CLUSTER PROTECTION In order to protect grapes from heat damage, in warm climates it is prudent to develop the vineyard with row orientation and trellising that will protect clusters from direct radiation at the warmest part of the day. The highest cluster tempera- tures occur with exposed bunches on the west side of rows that have a north-south orientation with a vertical shoot position (VSP) trellis, because their maximum radiation interception coincides with maxi- mum temperatures in the afternoon. ern California vineyards, this is usu- ally around 20 to 30 degrees. TRELLIS SYSTEM MATTERS Trellis design can also be used to shade and protect grapes. VSP trellises have many advantages in terms of easy manipulation of the canopy, creating a relatively uniform and exposed environment around the clusters for sun exposure and air flow, which helps to achieve disease control and uniform ripen- ing. However, care must be taken in a VSP system not to overexpose the clusters, so minimal or no leaf removal should be employed on the afternoon sun side. A modified VSP that uses several narrow cross arms, either of equal or increasing width for the upper cross arms, will provide additional shading. However, shoots may need to be tied to the wires in this case, especially in windy areas. Other trel- lis systems that utilize wider cross SOIL & CELLAR REMI COHEN