sumac rust

Symptoms

Numerous bright yellow to orange flecks appear on the upper surface of the sumac leaflets, with matching raised pustules (uredinia, later telia) erupting on the underside directly beneath them. The pustules are powdery and rusty-brown to cinnamon, and rub off as a coloured spore dust onto a finger or cloth. Heavily infected leaflets yellow, curl and drop prematurely from midsummer onward, thinning the canopy. Repeated annual defoliation weakens the shrub and reduces berry (drupe) set and quality.

Plants affected

• Sicilian sumac

Easily confused with

• sumac leaf spot

  How to tell them apart: Sumac rust (Pileolaria azerii) makes raised, powdery rusty-brown pustules on the LEAF UNDERSIDE that shed coloured spore dust when rubbed, with matching yellow flecks above. Sumac leaf spot (Phyllosticta rhoina) instead makes flat, dry, angular brown spots mainly on the UPPER surface, each ringed by a yellow halo with a greying centre and no spore powder (sometimes tiny black pycnidia dot the dead tissue). In short: erumpent powdery pustules underneath = rust; dry flat haloed spots on top = leaf spot.

Common questions

How do I recognise sumac rust on Sicilian sumac?

Numerous bright yellow to orange flecks appear on the upper surface of the sumac leaflets, with matching raised pustules (uredinia, later telia) erupting on the underside directly beneath them. The pustules are powdery and rusty-brown to cinnamon, and rub off as a coloured spore dust onto a finger or cloth.

Do I have to report sumac rust?

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

How is sumac rust 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.