Powdery mildew
production, so the net effect of the RH is very small. Wind and draught in greenhouses promote disease. In greenhouses, dispersal of spores over small distances [...] through the stomata and there are more stomata on the underside of the leaf. On the upper side, yellow spots are noticeable. In case of a severe epidemic, the [...] water and ‘hides’ on the underside of the leaves. Therefore, this is where the colonies mostly occur in these crops. In covered roses, the colonies appear first