Powdery mildews are just one of handfuls of different white structures on the surfaces of plants and one of many more infections to reduce the vigour, yield and beauty of our favourite garden plants and most important crops.
Powdery mildew can cause a number of different visible imperfections in their hosts: discolouratation is one such feature, but symptoms suc has that seen on the Heracleum below is more likely to be due to a virus.
Powdery mildew typically forms a white, ‘talcum-powder-like’ coating on the surfaces of plants. But this feature is certainly not exclusive to the #PowderyMs: of the other fungi to spread their white, mycelial-forming hyphae the most prominent is Botrytis, a ‘grey-rot’ which kills its host. Below are some of my own samples with Botrytis causing confusion…
Finally the hairs typical on many plant species can catch the powdery-mildew-trained-eye and can easily be confused as surface mycelium. Below is an example of a Vicia sp. and of course a Stachys sp. on which it is particularly hard to identify a powdery midlew beneath its typical furry leaf covering.