The control of one of the most important disease in the cultivation of lettuce heavy under glass, downy mildew and powdery mildew, caused by the fungus Bremia lactucae, relies mainly on chemical control, in combination with the use of resistant slavariëteiten. Although this system proves its worth in the current crop of lettuce, growing awareness - even with the growers themselves - that this way of working time will no longer be tenable. Because the resistances are relatively easy, and still rapper to be broken, is also deal with the systematic chemical recommended in addition to the use of these varieties (so-called. Calendar spraying). It handles to keep the grower at specified times without taking into account the potential risk of infection. Bovendie this is done with a limited number of resources. The combination of the use of low agents to a high-frequency working resistance of the fungus towards the fungicide in the hand. The frequent use of chemicals also gives rise to residues and this is strictly enforced. Reducing the use of chemical plant protection is desirable, not only for the health protection of the consumer and the operator, but also the environment and for the image of the Belgian lettuce. In greenhouses the possibility climate, irrigation, ... send in order to keep the mold from the crop, but for there to be large gaps in the epidemiology of Bremia lactucae. A better knowledge of this is also required. This project mainly aims to develop knowledge of Bremia lactucae and the finalization of a workable recommendation system for the individual grower.