Columbine powdery mildew

Symptoms

A fine white-to-greyish powdery, mealy coating develops mainly on the upper surface of columbine leaves and leaflets, but also on stems, leaf stalks, buds and flowers. Early patches look like dusty flour spots that enlarge and merge until whole leaflets are coated and can take on a netted or grainy appearance; underlying tissue may turn pale or purplish. Heavily infected leaves yellow, dry out, curl and drop early, and flowering is reduced. The coating wipes off easily with a finger, and the disease is worst in warm, humid, crowded plantings even when the foliage stays dry.

Plants affected

• columbine (granny's bonnet)

Easily confused with

• columbine downy mildew

  How to tell them apart: Both Erysiphe aquilegiae (columbine powdery mildew) and Peronospora aquilegiicola (columbine downy mildew) coat Aquilegia leaves with a 'mould', but in opposite ways. Powdery mildew is a dry, white-grey, mealy dust mainly on the UPPER leaf surface that wipes off with a finger, spreads in warm humid weather, and leaves the leaf shape intact at first. Downy mildew shows a greyish-violet, felty fuzz on the LOWER surface only, sitting beneath angular yellow-to-purple blotches that are bounded by the leaf veins; the foliage becomes distorted, pale and overlong, leaves curl, brown and collapse, and it spreads in cool, wet conditions. If the bloom is on top and rubs off = powdery mildew; if it is underneath with vein-limited discoloured patches and twisted leaves = downy mildew.

Common questions

How do I recognise Columbine powdery mildew on columbine (granny's bonnet)?

A fine white-to-greyish powdery, mealy coating develops mainly on the upper surface of columbine leaves and leaflets, but also on stems, leaf stalks, buds and flowers. Early patches look like dusty flour spots that enlarge and merge until whole leaflets are coated and can take on a netted or grainy appearance; underlying tissue may turn pale or purplish.

Do I have to report Columbine powdery mildew?

No. Columbine 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 Columbine 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.