A VACUUM COLLECTION AND SEED SEPARATION TECHNIQUE FOR ENUMERATION OF SCLEROTIA OF CLAVICEPS-PURPUREA IN PERENNIAL RYEGRASS FIELDS

A portable electric wet-dry shop vacuum run by a gas-powered generator was used to collect sclerotia of Claviceps purpurea from 1-m2 areas i n a commercial field of perennial ryegrass. Sclerotia were separated f rom soil and straw residue using an air-screen (seed separation) machi ne, in which samples were partitioned based on particle width and thic kness, and terminal velocity. The procedure also was used to determine the number of sclerotia in bales of annual ryegrass straw. Efficiency of recovery of sclerotia using the air-screen machine with known numb ers of ergot was 98-100%. Recovery by vacuum collection in the field o f a known number of sclerotia distributed over surface residue and pla nt crowns was 83% +/- 4% in areas without soil cracks, 73% +/- 15% in areas with deep soil cracks, and 79% +/- 13% in areas selected at rand om. In perennial ryegrass with 23% of heads infected (two sclerotia pe r infected head), 39 sclerotia per square meter of soil surface were r ecovered.