Powdery mildew

Powdery mildew is a common plant disease caused by obligate fungi of the family Erysiphaceae. Unlike many other plant pathogens, these fungi grow primarily on the surface of the plant tissue, forming a fine, white, web-like mycelium. They extract essential nutrients from the host plant using specialized structures called haustoria, which penetrate the plant cells without immediately killing them.

The host range of Erysiphaceae is exceptionally broad, affecting a vast array of agricultural, ornamental, and horticultural crops. Major victims include cereals, grapevine, cucurbits (cucumbers, melons), legumes, and various fruit trees. Since the fungi are host-specific, different species are responsible for infecting different types of crops, but the symptoms remain characteristic across the board.

Typical symptoms manifest as white, powdery patches on leaves, stems, and sometimes buds or fruit. As the infection progresses, these patches expand and merge, often causing the underlying tissue to turn yellow, curl, or become distorted. In late stages, small dark spots known as cleistothecia appear, which serve as the overwintering structures of the fungus.

Development and spread of powdery mildew are strongly linked to specific environmental factors. The disease thrives in warm, dry to humid conditions. While high humidity favors spore germination, free water on leaf surfaces is often detrimental to the fungus, which distinguishes it from downy mildew. Poor air circulation and rapid fluctuations between day and night temperatures are primary drivers of outbreaks.

Economic damage is caused by reduced photosynthetic capacity, stunted growth, and lower quality of yields. Preventing and managing this disease requires an integrated approach to maintain crop health and minimize infection pressure. Key strategies include:

• choosing resistant cultivars that are naturally less susceptible;
• maintaining proper plant spacing to improve air circulation and reduce humidity;
• applying fungicides containing sulfur, systemic triazoles, or strobilurins when symptoms appear;
• avoiding excessive nitrogen fertilization, which creates soft, vulnerable tissue;
• regular sanitation, including the removal of infected plant debris to reduce overwintering spores.