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G R A P E GS M W RN GV I T I C U L T U R E RO A I T by Dr. Richard Smart Double-header solution for high-vigor vines in cool climates I nnovation by grape growers always amazes me. Certainly this is not the sole prerogative of viticultural scientists. Here is a story of how an individual grower has made an advance that might help us all. Terry Bennett, owner of Home Hill Vineyard, south of Hobart, Tasmania, in Australia's Huon Valley, planted the vineyard with his wife Rosemary in 1993, in what was previously an apple-growing area. Home Hill is one of Australia's coolest vineyards, being among the southernmost. Vigor problems in a cool vineyard The 15-acre vineyard extends down a north-facing slope (remember this is the southern hemisphere) and onto flats. As is common in such situations, there are frost and vigor problems on the flats. The cold air accumulates, and also the soils are deeper. Frost control is a separate issue from vigor control. Vines were planted with 8-foot by 5-foot spacing and trained to a vertical shoot position (VSP) trellis. The vines on the slope were balanced and produced nice fruit with good vegetative growth. However, the vines on the flats were too vigorous, with shaded canopies, restricted fruit ripening and poorly colored wines. Any amount of crop thinning made the problem worse, certainly no better. The yields were poor at the beginning, made worse by crop thinning. Figure 1. A typical good canopy of a "big" vine trained to the double header system. Notice lack of shading, many canopy gaps, good leaf and fruit exposure. "Big Vine" theory turned practice Bennett pondered on a solution and turned to Sunlight into Wine, where he found the section about the big vine theory. I must say I am inclined to change the title of this section, because this practice is no longer a theory but wellproven. The idea is that high vine vigor is due to an imbalance between the size of the root system and the number of buds left at winter pruning. A big root system and few buds creates excessive vegetative growth. If there are too few buds left at pruning, the large root system produces hormones and nutritional supply that encourages shoot growth following bud burst. If too few buds have been left at pruning, the number of shoots is restricted. Therefore, those few shoots will grow vigorously and the internodes will be long, the diameter large and shoot growth very rapid. Most of the lateral buds on the shoot will break, and there will be many lateral shoots with strong, active growth. Creating balanced vines using Golden Rules The way to balance excessive shoot growth is to leave more buds at pruning, so the effect of the root system is effectively diluted. One Golden Rule is to leave around 30 buds per kilogram of pruning weight, or 13 buds per pound. But the dilemma of stacking buds on the same vine is that it creates excessive 68 p r acti c al w i ne ry & v i n e yard J U LY 20 13 15/05/13 14:10