Farm-level Forecasting: its Role and Organization in Plant Protection1

Forecasting in plant protection has two principal objectives. It should support decision making both on the necessity of control measures and on the correct timing of their application. Regional forecasts may guide plant protection activities on farms, but they have to be supplemented by local observations on the key pests of the most important crops. It is concluded that the organization of farm-level forecasting is closely related to certain characteristics – degree of harmfulness and oligophagy – of pests and diseases. Regular control is necessary of the most harmful pests whose economic thresholds lie below the general ecological equilibrium, and the correct timing of treatments should be accurately determined by means of local forecasting techniques. On the other hand, the harmful organisms whose economic thresholds lie above the general ecological equilibrium require comparison between the economic thresholds and the actual local densities. These observations should be carried out either by individual workers or by temporary working groups, depending on objective and on the area to be controlled. La prevision phytosanitaire doit satisfaire aux deux exigences principales suivantes: determiner la necessite d'une intervention et en fixer la frequence. Les previsions regionales fournissent des indications aux producteurs, mais ceux-ci doivent assurer leurs propres observations locales sur les depredateurs les plus importants. La facon de concevoir les previsions au niveau du producteur depend de I'impact economique et de L'oligophagie des organismes nuisibles concernes. Si les seuils economiques de ceux-ci se situent en general au-dessous d'un certain equilibre ecologique, il faudra prendre les mesures de protection et les systemes de previsions locales serviront a determiner les dates precises des interventions. En revanche, lorsque les organismes nuisibles ont des seuils de tolerance economique depassant generalement I'equilibre ecologique, il faudra comparer les seuils economiques a la densite des populations enregistree. Suivant I'ampleur de la tiche, celle-ci pourra être accomplie individuellement ou par un groupe de travail.