Black Stem Rust - Puccinia graminis

Streaky rust-brown uredinia appear on the leaves, leaf sheaths, stems and glumes of the primary hosts, grasses and cereal crops. Later, darker telia appear,  particularly on the leaf sheaths and stems, but are not gall-causers.

The alternate host is Berberis or Mahonia, and is rare, and a gall-causer; the rust causes raised areas on fruits and undersides of leaves, yellow to orange-red to purplish; bearing spermogonia and aecia only. 

Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

The rust affects wheat, oats, barley, rye and various grasses.

Late summer and early autumn.

Black stem rust is spread by means of wind borne spores. There is an overwintering stage which re-infects crops via an intermediate host, the shrub barberry. In the UK, barberry is not believed to be an important factor in disease spread. Epidemics usually start from wind borne spores from continental Europe.

Widespread in the southern half of Britain.

Status in Leicestershire and Rutland not known.