and over-ripening, there is a propensity for the wine to develop flavours of cooked or stewed blackcurrants. The Cabernet grape variety has thrived in a variety of vineyard soil types, making the consideration of soil less of a concern, particularly for New World winemakers. In Bordeaux, the soil aspect of terroir was historically an important consideration in determining which of the major Bordeaux grape varieties were planted. While Merlot seemed to thrive in clay- and limestone-based soils (such as those of the Right Bank regions of the Gironde estuary), Cabernet Sauvignon seemed to perform better in the gravel-based soil of the Médoc region on the Left Bank. The gravel soils offered the benefit of being well drained while absorbing and radiating heat to the vines, aiding ripening. Clay- and limestone-based soils are often cooler, allowing less heat to reach the vines, and delaying ripening. In regions where the climate is warmer, there is more emphasis on soil that is less fertile, which promotes less vigour in the vine, which can keep yields low. In the Napa Valley wine regions of Oakville and Rutherford, the soil is more alluvial and dusty. Rutherford Cabernet Sauvignon has been often quoted as giving a sense of terroir with a taste of "Rutherford dust". In the South Australian wine region of Coonawarra, Cabernet Sauvignon has produced vastly different results from grape vines planted in the region's terra rosa soil – so much so that the red soil is considered the "boundary" of the wine region, with some controversy from wine growers with Cabernet Sauvignon, planted on red soil. In addition to ripeness levels, the harvest yields can also have a strong influence on the resulting quality and flavours of Cabernet Sauvignon wine. The vine itself is prone to vigorous yields, particularly when planted on the vigorous SO4 rootstock. Excessive yields can result in less concentrated and flavorful wine with flavours more on the green or herbaceous side . In the 1970s, a particular clone of Cabernet Sauvignon that was engineered to be virus free was noted for its very high yields-causing many quality-conscious producers to replant their vineyards in the late 20th century with different clonal varieties. To reduce yields, producers can plant the vines on less vigorous rootstock and also practice green harvesting with aggressive pruning of grape clusters soon after veraison. In general, Cabernet Sauvignon has good resistance to most grape diseases, powdery