rose powdery mildew

Symptoms

White powdery coating on new growth, distorted buds.

Plants affected

• rose

Easily confused with

• rose black spot

  How to tell them apart: Rose black spot (Diplocarpon rosae): black blotches with feathery, fringed edges on the upper leaf, surrounding yellowing and early leaf drop, worst in wet summers. Rose powdery mildew (Podosphaera pannosa): white powdery coating on young leaves, buds and shoot tips that distorts and curls them, worst in dry weather with cool nights.

• grey mould (Botrytis)

  How to tell them apart: Botrytis cinerea (grey mould) on roses shows a fuzzy, grey-brown felt-like coating on buds, petals and dying flowers, often with soft, water-soaked brown rot; infected buds fail to open ('balling') and develop a slimy mush in cool, damp, still air. Podosphaera pannosa (rose powdery mildew) instead forms a dry, flour-white to slightly grey powdery dusting on young shoots, leaf surfaces and flower buds, with curled, distorted and reddish-tinged new growth; it thrives in warm days with humid nights but dry leaf surfaces. Key tell: grey mould is fuzzy, grey and wet/rotting, while powdery mildew is white, dry, dusty and wipes off the surface.

Common questions

How do I recognise rose powdery mildew on rose?

White powdery coating on new growth, distorted buds.

Do I have to report rose powdery mildew?

No. rose powdery mildew is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is rose powdery mildew treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.