The effectiveness of several natural products in field trials were tested against powdery mildew on courgette. Sulphur, sodium bicarbonate (alone or in mixture with pinolene, mineral oil or sulphur), sodium silicate in mixture with mineral oil, potassium permanganate, lecithin, Equisetum arvense in mixture with Timus vulgaris, Ampelomyces quisqualis and Reynoutria sachalinensis were evaluated. Generally, in our working conditions (very strong pathogen infection), only some products were effective. Good results were obtained using sulphur and potassium permanganate in the first year and very interesting results about disease control were obtained, in the second year of the trial, using sulphur alone or in mixture with sodium bicarbonate. The products tested did not show any phytotoxic symptoms.