The effect of crown rust (Puccinia coronataCorda) on the yield and botanical composition of two ryegrass/white clover pastures

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Abstract
The effect of crown rust (Puccinia coronata Corda) on the yield and botanical composition of swards of ‘Grasslands Ruanui’ perennial ryegrass (Lolium perenne L.) and ‘Grasslands Ariki’ ryegrass (Lolium (multiflorum X perenne) perenne), both growing in association with ‘Grasslands Huia’ white clover (Trifolium repens L.), was studied in a plot trial at two cutting frequencies. As in previous experiments with pure swards (Lancashire and Latch 1966), the incidence and effects of crown rust on ryegrass growth were greater in Ruanui than Ariki and were reduced by mowing. In the mixed sward this depression of ryegrass yield resulted in marked clover dominance, particularly with Ruanui (80% clover), in the infrequently mown rusted swards. In addition, crown rust caused a greater reduction in the yield of green ryegrass (84%) in the Ruanui ryegrass/white clover sward than in pure Ruanui swards (42%–64%) in other experiments with a similar level of disease incidence. The results are discussed in relation to the different effects of grazing and mowing on ryegrass/white clover pastures; the grazing management and botanical composition of these pastures in the summer and autumn; and the effects of crown rust on the growth of ryegrass in pure and mixed swards.