Bulletin #1014, Ergot of Barley and Other Small Grains (PDF) Developed by Steven B. Johnson, Extension Crops Specialist For information about UMaine Extension programs and resources, visit extension.umaine.edu.Find more of our publications and books at extension.umaine.edu/publications/. Ergot is a disease of cereal crops and grasses caused by the fungus Claviceps purpurea, which infects developing grains.