Contamination and persistence of endophyte-free ryegrass pastures established by spray-drilling, and intensively grazed by dairy cows in the Waikato region of New Zealand

The contamination of endophyte-free ryegrass (Lolium perenne) pastures with volunteer endophyte-infected ryegrass, and the persistence of endophyte-fr ee ryegrass, were studied over three years at the Dairying Research Corpora tion, Hamilton, New Zealand. Plots were sprayed with glyphosate herbicide i n mid March 1996 (sprayed: S), or mid March and again in mid April (double sprayed: D). A sub-plot treatment allowed the effects of the presence or ab sence of white clover (Trifolium repens) to be studied. All plots were dire ct-drilled with endophyte-free perennial ryegrass in late April 1996, and w ere subsequently rotationally grazed by dairy cows. Sources of contaminatio n were endophyte-infected ryegrass seed from reseeding of existing ryegrass , seed consumed by cows and deposited in dung, and seed buried in the soil, with endophyte infection levels after germination of 66, 38, and 75%, resp ectively. incomplete kill of existing endophyte-infected ryegrass after her bicide applications was another possible source of contamination with a 50% endophyte infection level. Contamination of D plots was consistently less than in S, averaging 25 and 58%, respectively, after three years, but was < 10% of plants in D plots over the first two years. Reseeding of existing en dophyte-infected ryegrass was considered the most important source of conta mination and the soil seedbank the least. Double spraying reduced competiti on for establishing endophyte-free ryegrass, which consistently improved ry egrass survival compared with S, reflecting a higher pasture ryegrass conte nt for 12 months, but no improvement in herbage accumulation. White clover level did not influence contamination. The trial showed that an endophyte-f ree ryegrass pasture could be maintained for at least 3 years showing simil ar trends in yield and persistence as high-endophyte based ryegrass pasture s previously monitored at the site.