A TFI calculation takes into account two types of doses: approved dosages that may vary according to the nature of the sprayed product, and the applied dose which, during a treatment, is often lower than the approved dose, and which can vary as decided by the winegrower. The calculation also takes into account two treatment areas: the area to which the treatment is applied, and the total area of the plot or vineyard.
For example, it is possible to treat the entire vineyard with different products and/or doses for several reasons (greater vigour in a part of the plot, some plots may be located at the bottom of a basin where humidity is higher, some plots may be close to a forest). In this case, it is necessary to identify the area treated for each treatment product.
Situation and calculation example 1:
On Thursday, 16 April, an anti-mildew is sprayed on a 1-hectare plot at a rate of 1 kg/ha. The product used is approved at 4kg/ha. The TFI will be: (1/4) * 1 = 0.25
On Monday, 20 April, after a very rainy weekend that caused the product applied earlier in the week (50 mm) to leach out, the same anti-mildew product is sprayed this time, at a rate of 2 kg/ha (the approved rate is still 4 kg/ha). The TFI for this operation will be: (2/4) * 1 = 0.5
At the end of the year, all the TFIs are added together to obtain the total TFI. In this case, the total TFI is: 0.25 + 0.5 = 0.75.
Situation and calculation example 2:
On Friday, 24 April, an anti-mildew product is sprayed on a 1-hectare plot at a rate of 1 kg/ha. The product used is registered at 4 kg/ha. The TFI will be: (1/4) * 1 = 0.25
On Friday, 8 May, after vigorous growth in half of the plot, the same anti-mildew product is sprayed this time, at a rate of 2 kg/ha (the registered rate is still 4 kg/ha), on the vigorous half of the plot only. The TFI for this operation will be : (20.5/41) = 0.25
At the end of the year, all the TFIs are added together to obtain the total TFI. In this case, the total TFI is: 0.25 + 0.25 = 0.50.