205an aerial inoculum spray method. Wallace ( 1959 ) also succeeded in producing
infection and subsequent mortality as mature seeds in wheat and oats using this
method. In both studies, extended dew periods were required in order for successful
fl oret infection to occur, calling into question whether this process would ever occur
naturally in the semiarid environments where these annual grass weeds are a prob-
lem. We approached this question indirectly by examining P. semeniperda disease
Fig. 7.3 ( a ) Bromus tectorum seed killed by Pyrenophora semeniperda , showing the protruding
stromata that engendered the moniker ‘black fi ngers of death’, ( b ) Bromus tectorum seed density
in different categories as measured monthly during a fi eld seed bank study in 2005–2006 at the
Whiterocks exclosure in Skull Valley, Utah. (For each date 20 seed bank samples were collected
and processed as described for the cheatgrass disease survey), ( c ) Densities of viable and killed
seeds in the seed bank at Haven Flats on the Hanford Reach National Monument in spring 2010
after application of P. semeniperda inoculum at three levels the previous fall ( n = 10 for controls
and n = 40 for inoculated plots, i.e., mean of four pathogen strains at each inoculum level. Data
were obtained from seed bank samples collected from each plot as described earlier)
7 Community Ecology of Fungal Pathogens on Bromus tectorum