Stem rust ( Puccina graminis ) identified on spring barley in the UK adjacent to infected Berberis vulgaris

Wheat stem rust caused by the fungus Puccinia graminis f.sp. tritici is a notorious disease of wheat and barley (Leonard & Szabo). In western Europe, following many decades of absence the disease started to re-emerge in 2013 with sporadic wheat stem rust outbreaks reported in Germany, Sweden and Denmark (Hovmøller). In the same year a single wheat plant infected with stem rust was discovered in the UK, which marked the first record of the disease in over 60 years (Lewis et al.). These initial outbreaks were seen as an early warning of the potential resurgence of a forgotten foe (Saunders et al.). Accordingly, a much larger outbreak was recorded in Sicily in 2016 (Hovmøller).