Smut of rye [Urocystis occulta]
Pattern of damage
Initially, dark blisters appear in stripes on the stem and leaf tissue and on the insides of the boots. The sporangia may merge on the leaves and occupy as much as 2/3 of the leaf length. They eventually rupture and release black smut spores. Infected stems are noticeably stunted and sometimes twisted. The heads frequently remain with the awns trapped in the upper portion of the boot and the grain fails to develop.
Pathogen-free seed. Avoid sowing too early and too deeply. Refrain from planting rye for 1 year after a severe infection. Control couch grass, as it is also a host plant of stripe smut. Fungicide measures: Treat seeds with a fungicide seed treatment.
Spread/transmission: Spores are either seed-borne or soil-borne. After the rye is sown, the smut spores germinate and infect the seedlings. The mycelium grows systemically upwards in the rye stem and the characteristic swellings and sporangia develop.