Leaf of a courgette plant, Curcubita pepo, showing infection with powdery mildew. The picture shows a mature leaf of a courgette plant growing in late September in the UK. The white powdery covering is a mat of fungal hyphae, and the yellow patches represent areas that have been damaged by the fungus. Part of a killed leaf is visible top to left (brown). The most common species to affect courgettes are Erisyphe cichoracearum and Sphaerotheca fuliginea. The fungi spread by means of conidia.Infections are most common in hot dry spells of weather, and may lead to the death of individual leaves or even of whole plants. The fungi overwinters on plant debris. In a garden good hygiene and judicious watering of plants will help to avoid the disease