Seasonal Availability of Inoculum of Stagonospora nodorum in the Field in the Southeastern U.S.

The presence of inoculum of Stagonospora nodorum was detected by placing wheat seedlings in the field for short periods throughout the year. Inoculum was monitored in growing wheat crops, on wheat stubble, and in adjacent fields of tall fescue over a three year period. S. nodorum was found throughout the year but was detected least often during the summer months and in October, the driest month of the year. Seedlings became infected when placed in wheat stubble up to 22 months after wheat was harvested. S. nodorum was infrequently found in the tall fescue within 17 m from the edge of the wheat fields. The wheat biotype of S. nodorum was recovered from wheat and barley seedlings, but the barley biotype was not found. The results show that inoculum of S. nodorum is produced within a field and is disseminated only short distances. The results provide additional circumstantial evidence that the asexual stage is the source of inoculum in the southeastern U.S.