Growth and persistence of perennial and hybrid ryegrasses when grazed by dairy cows in the central Waikato region of New Zealand

A 3-year plot trial was conducted at the Dairying Research Corporation, Ham ilton, New Zealand to compare herbage production, persistence, and crown ru st (Puccinia coronata) resistance in 13 newly released cultivars or coded r yegrass lines. These included perennial (Lolium perenne) and hybrid (Lolium x boucheanum syn. Lolium hybridium) lines being compared with the standard perennial ryegrass varieties 'Yatsyn 1' and 'Grasslands Nui'. Plots of eac h line were arranged in a randomised block design with 4 replicates, and we re sown into a cultivated seedbed with white clover (Trifolium repens) in M arch 1992. Plots were rotationally grazed by dairy cows. Yields of ryegrass were less in Year 2 than Year 1, with an average decline of 27% (13 805 ve rsus 10 096 kg DM ha(-1)). Average ryegrass yields in Year 3 were 6% below Year 2 (10 096 versus 9516 kg DM ha(-1)). Apart from the tetraploid hybrid 'Grasslands Greenstone' and an Uncertified Perennial ryegrass line, there w ere few differences in average total ryegrass yield. After 3 years the freq uency of point hits on ryegrass averaged <50%, and, since 'Yatsyn 1' had th e highest average frequency (4 6%), we concluded that persistence of the ne wly released lines was no better than the standard in this trial. 'Greensto ne' and Uncertified Perennial were the most susceptible to crown rust and ' Grasslands Impact' was the least affected.