Surveys are essential to establish the percentage of vines to be replaced. It is possible to make an initial survey of the plot to mark any diseased plants to be uprooted, and then a second passage on a set number of rows to calculate the final percentage to be replaced. This method is the most reliable and also enables planning of the labour and equipment required.
Calculation method for 10 rows:
A = Total number of dead or missing plants
B = Number of theoretical healthy plants per row
C = Number of rows (10 in this example)
D = Total percentage of dead or missing plants (%)
D = (A / BC) 100
It is possible to implement this method on a varying number of rows depending on the plot's area and also its heterogeneity. It is also possible to attribute uncertainty to the operator's observations. An uncertainty of 10% will give the following calculation:
E = D-(D*10%) or E = total percentage of dead or missing plants (%) with an uncertainty of 10%.
Remote sensing can also be used to map the vineyard. This consists of infrared sensors placed on satellites or flying devices (planes, drones) that measure the radiation reflected by the vegetation. By using this method, it is easy to obtain an overall view of the plots and of the areas without vegetation, which generally correspond to missing or diseased vines.
The counting methodology at Château Latour: every year after the harvest, during pruning, dead or very damaged vines are uprooted. At the same time as the holes are being made, the tractor operators count them to determine the number of vines to be ordered. Later, during planting, another survey is performed in order to adjust the actual number of vines to be planted. GPS counting is still being developed and is combined with the traditional counting method. Each newly planted vine is marked by GPS.