Since 2006, a new EC regulation has imposed 2.0 µg/l as the upper limit for OTA concentration in wines (CR 1881/2006). OTA production results from a harmful combination of skin lesions and favourable conditions for A. carbonarius growth, namely the air temperature and humidity, and the berry sugar content. The aim of our research was to highlight in vivo interaction between the number of damaged berries and the conditions for fungus development in relation to OTA concentration in wine. A survey carried out on the 2005 production from 156 vineyards bordering on the French Mediterranean enabled a link to be made between information on crop management, vineyard characteristics, meteorological data and the OTA concentration in wine. With humid air conditions during the susceptible berry period of 20 days before harvest, combined with a large number of damaged berries and a temperature conducive to both fungus growth and OTA production, critical levels of OTA concentration in wine were observed. Within the range of average daily air temperatures investigated, from 17.2 to 22.8 °C, during the susceptible berry period, 21 °C appeared to be the lower limit below which fungus growth and OTA production were not sufficient to result in critical levels of OTA concentration in wine. In our experiment, an average daily air temperature under 21 °C corresponded to an average minimum daily air temperature under 15 °C, below which fungus growth stopped under in vitro conditions. The importance of the berry sugar content before harvest was also demonstrated and our results suggest that the risk of wine contamination by OTA might be predicted from the number of damaged berries and the berry sugar content, along with climate monitoring.