Foliar application is a solution primarily for use in situations where there is a proven deficiency in the vineyard. This is a temporary solution to a problem that must then be corrected in the long term at the soil level.
2.6.4.d Foliar application
Is it necessary to apply nitrogen at a particular time?
For the production of thiolated white wines, the addition of foliar nitrogen combined with sulphur increases the proportion of varietal thiols in the wine and thus enhances the aromatic characteristics of certain grape varieties such as Sauvignon Blanc or Colombard. This application should be made at véraison.
In the case of a vineyard covered with grass due to load-bearing problems, if it turns out that the grass cover is too competitive, an application can also be considered in order to compensate. The cover will then have to be reduced or removed from the vineyard the following year, or a more substantial quantity of soil improver will have to be applied. See grass management for more details.
What are the current year's weather conditions?
In the case of a drought, for example, some minerals are difficult for the vine to assimilate (induced deficiency). This is the case of manganese for example. A foliar contribution around flowering is then a good solution.
If the year is extremely rainy and/or the soil tends to retain water excessively, boron may become unavailable to the vine. A foliar application two to four weeks before véraison is then possible.