Summary Because powdery mildew is one of the bigger problems today in the cultivation of cucumbers for which there are no good control methods, it has been of great interest to study this particular problem. The work describes how silicon affects mildew, primarily in cultivation of cucumbers. The purpose of this work was that through literature studies find out how silicon works in the plant and if it can contribute to the control of powdery mildew. I have mainly carried out literature studies, but also a conducted cultivation trials in our own cultivation. . I have also discussed with the cultivation advisors in the greenhouse industry today. The results show an effect of silicon that inhibits powdery mildew and delays the infection. With a combination of irrigation and foliar fertilization you can probably get good results in the control of powdery mildew