A field trial of crown rust (Puccinia coronata f. sp avenae) as a biocontrol agent of wild oats on San Clemente Island

San Clemente Island has been subjected to large-scale disturbance from graz ing and subsequent weed infestation, particularly by two wild oat species, Avena fatua and A. barbata. An endemic disease, crown rust (caused by Pucci nia coronata f.sp. avenae), was selected as a potential control agent. A st rain with a short latent period was selected from a common island isolate. Three replicate sets of plots were established on the island, each set cont aining a plot treated with crown rust, a control plot, and a plot treated w ith a fungicide. Disease was assessed in these plots and outside of the ino culated plots to a distance of 100 m. Reproductive output of wild oats from these plots was measured and compared for differences among treatments. Re sults indicated that disease was established from artificial inoculations i n both years, 2 weeks earlier than the onset of disease from natural infect ions in 1997, but not in 1998. This result may have been due to unusual wea ther patterns in 1998 that caused an earlier onset of natural infections an d precluded higher success of artificial inoculations early in the season. Analysis of reproductive output of wild oats from these plots showed that b iomass and seed number were significantly lower (P < 0.05) in inoculated pl ots than in control and fungicide-treated plots. These results indicated th at, with augmentation over several years, crown rust may be effective in re ducing populations of wild oats on San Clemente Island. (C) 2000 Academic P ress.