A Field Trial of Crown Rust (Puccinia coronata f. sp. avenae) as a Biocontrol Agent of Wild Oats on San Clemente Island

Abstract

San Clemente Island has been subjected to large-scale disturbance from grazing and subsequent weed infestation, particularly by two wild oat species, Avena fatua and A. barbata. An endemic disease, crown rust (caused by Puccinia coronata f.sp. avenae ), was selected as a potential control agent. A strain with a short latent period was selected from a common island isolate. Three replicate sets of plots were established on the island, each set containing a plot treated with crown rust, a control plot, and a plot treated with a fungicide. Disease was assessed in these plots and outside of the inoculated plots to a distance of 100 m. Reproductive output of wild oats from these plots was measured and compared for differences among treatments. Results indicated that disease was established from artificial inoculations in both years, 2 weeks earlier than the onset of disease from natural infections in 1997, but not in 1998. This result may have been due to unusual weather patterns in 1998 that caused an earlier onset of natural infections and precluded higher success of artificial inoculations early in the season. Analysis of reproductive output of wild oats from these plots showed that biomass and seed number were significantly lower ( P < 0.05) in inoculated plots than in control and fungicide-treated plots. These results indicated that, with augmentation over several years, crown rust may be effective in reducing populations of wild oats on San Clemente Island.