Ryegrass contamination of endophyte-free dairy pastures after spray drilling in autumn

Abstract

Ryegrass contamination of endophyte-free ryegrass (Lolium perenne L.) pastures, established by autumn spray-drilling of existing endophyteinfected pasture, was studied over one year at the Dairying Research Corporation, Hamilton. Main plots were sprayed with glyphosate at 1.44 kg a.i./ ha (4 l/ha of Roundup G2) in mid-March 1996 (S), or mid March and again in mid April (D). White clover (Trifolium repens L.) was removed from half the area of each main plot using herbicide and the remainder was drilled with white clover. All plots were direct drilled with endophyte-free perennial ryegrass in late April. Plots were rotationally grazed by dairy cows. Volunteer perennial ryegrass seedlings that germinated from seed in dung pats, on the soil surface (reseeding) and after recovery from the seed-bank, contained 40, 66 and 69% endophyte, respectively. The largest inputs of volunteers came from dung and reseeding. The average dung pat covered 0.08 m2 and supported 3 volunteer ryegrass seedlings (range 0- 14). After the first spraying 0.87 ryegrass clumps/ m2 were surviving, and 0.13/m2 survived both herbicide applications; half were infected with endophyte. After one year, contamination of S was 2.5 times higher than D plots (18 vs 7% of plants endophyte infected), showing that double spraying in autumn was effective at reducing contamination to a low level. Keywords: dairy pastures, dung, endophyte, Lolium perenne, reseeding, seed-bank, seed transfer, volunteer ryegrass