Abstract
Assessing the risk associated to a pest is a key aspect of management. Using Xylella fastidiosa as an example, we show that risk evaluation requires a good knowledge of the pest biology and its potential vectors, reliable and efficient detection techniques as well as a good experience of modeling tools. Knowledge of the economic and environmental context is also an important aspect of the problem. When a new pest occurs, authorities rarely have this information. Yet, speed is a determining factor ineffective management of phytosanitary crises. The assessment and anticipation of pest risks are therefore key elements of the management strategy for pests and diseases of crops and forests.