Effects of natural reseeding and establishment method on contamination of a novel endophyte-infected perennial ryegrass dairy pasture with other ryegrass/endophyte associations

The contamination of a perennial ryegrass (Lolium perenne) dairy pasture infected with a novel endophyte with other ryegrass/endophyte associations was studied over 2 years in Hamilton, New Zealand. Five management treatments (turnip crop, usual rotational grazing, usual rotational Grazing followed by topping, silage making, hay making) were applied to produce a range of natural reseeding levels, and then three establishment methods (spray/cultivation, double-spray/fallow, hard-grazing) were used before drilling AR1 endophyte-infected perennial ryegrass (no lolitrem B or ergovaline production). Contamination from wild endophyte (Neotyphodium lolii)-infected perennial ryegrass, endophyte-free perennial ryegrass, wild endophyte-infected hybrid (L. boucheanum syn. L. hybridum)/Italian ryegrass (L. multiflorum), N. occultans endophyte-infected hybrid/Italian ryegrass and endophyte-free hybrid/Italian ryegrass tillers was determined. Contamination was assessed in the two summers following the autumn (May 2000) sowing by measuring lolitrem B concentration in bulk ryegrass samples and by sampling individual ryegrass tillers for endophyte identification in late summer of Year 1. Within the hard-grazed establishment treatment, the percentage of ryegrass tillers infected with AR1 in late summer of Year I was highest (73%) following the turnip crop pre-sowing treatment and lowest (4%) after hay making (SED = 5.3%, P < 0.001). The percentages of AR1-infected perennial ryegrass tillers in pastures established following spray/cultivation and double-spray/fallow treatments were 86 and 76%, respectively, compared with only 15% in the hard-grazed treatment (SED = 2.5, P < 0.001) (turnips excluded). The spray/cultivation and double-spray/fallow establishment treatments consistently had lower concentrations of lolitrem B in bulk ryegrass samples than the hard-grazed treatment, for example in early autumn of Year 1 (0.3, 0.5, 1.1 mg kg(-1) DM, P < 0.001) and Year 2 (0.1, 0.2, 1.0 mg kg(-1) DM, P < 0.001). Pasture production from August 2000 to August 2001 was similar following the spray/cultivation, double-spray/fallow and hard-grazed establishment treatments, averaging 14.9 t DM ha(-1). It is recommended that ryegrass pastures containing a novel endophyte be sown after a summer crop, or following a spray/cultivation or double-spray/fallow establishment method, instead of under-sowing into existing hard-grazed pasture. Methodology for assessing pasture contamination with different ryegrass/endophyte associations is also discussed.