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.

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.