A vocabulary of landscape — a landscape of words
1367 entries
mildew
Mildew is a thin surface growth of fungus on plants, fabric, paper, or damp walls, appearing as a white, gray, or downy film rather than as a fuzzy mass. In plant pathology the word covers two unrelated groups: powdery mildews, which look dusted with flour and grow on the leaf surface, and downy mildews, which are not true fungi at all and grow into the leaf from beneath.
Etymology
The word is Old English and it means honeydew. It originally named the sticky sweet deposit found on leaves, which people took for a kind of dew and which is in fact aphid excretion, and the name later transferred to the fungal growth that follows on the sugary residue. So a word for one thing ended up naming the thing that grows on it, and the original meaning is now carried by the word honeydew instead.
Notes
Powdery mildew is one of the few plant diseases that thrives in dry conditions, since the spores do not need free water to germinate, which is the reverse of nearly everything else. Downy mildew of grapes arriving in Europe from America in the 1870s led directly to the invention of Bordeaux mixture, the copper-and-lime spray that is still the standard organic fungicide.