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

Abstract

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 1 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‐in‐fected 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 14.9t 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.