Notes on McLaren Vale Irrigation and vigour strategies.
Reds ain't reds...
I found these notes from 2004 on the differences between McLaren Vale's big three red varieties. How much is still true in 2009?
I think the comments about water stress ring very true. Water stress, not to be confused with limiting water and drying soil, is a negative for wine quality.
Maintaining sufficient vigour to achieve fleshy rather than small berries was identified as the main issue with this variety. Too much fruit exposure is undesirable as it reduces colour in Cabernet berries. Excessive growth and shading can lead to undesirable flavours. It was noted that symptoms of stress in Cabernet Sauvignon are less obvious than in Shiraz and for this reason monitoring of soil moisture is a valuable management practice.
Shiraz in McLaren Vale is commonly over vigorous. Regulated Deficit Irrigation (RDI) after fruit set can help to slow shoot growth and reduce berry size. It was also noted that too much stress leading into and after veraison was not desirable as it can be detrimental to fruit quality. Canopy management, trellis design and irrigation were identified as important tools for controlling vigour. Bud dissections, pruning and yield records are thought to be useful in making pruning decisions that would ultimately achieve balance between fruit and foliage.
Vigour is a huge problem! Grenache is physiologically different to Shiraz as it will ‘shut down’ earlier on a hot day. Once established Grenache needs very little water or fertiliser. Grenache vines under aggressive RDI or dry grown seem to produce the best quality fruit. Shoot thinning on trellised vines, bunch thinning and use of competitive mid row crops to remove soil moisture are suggested as management options to achieve a balanced Grenache vine.