Effect of intensity and frequency of defoliation on growth of ryegrass, tall fescue and phalaris

Abstract

Pasture growth rates of ryegrass, tall fescue and phalaris were compared under combinations of 2 defoliation heights and 3 defoliation frequencies in mowing trials run in spring, summer, autumn and winter over 2 years. Lax defoliation gave on average 15%, 20% and 21% higher pasture growth rates than intense defoliation for ryegrass, tall fescue and phalaris pastures respectively over all seasons. Climate had a major influence on the response of all three pastures to defoliation management. In a dry spring, tall fescue produced most from a 15day cutting interval while for ryegrass and phalaris production was greatest from a 30day interval. In a wet spring, cutting frequency had no etfect, but a significant (P<0.01) interaction between height and frequency of defoliation occurred for all three pastures. In dry summer and autumn seasons, production was greatest under a l0- to 15day interval for ryegrass and tall fescue, but phalaris was not affected by defoliation frequency. In a dry winter, phalaris had highest growth rates under a 45day defoliation interval while the other two species were unaffected. In wet seasons defoliation management had little effect on growth rates. For maximum growth, defoliation management of tall fesuce differs from that of ryegrass in spring, while management of phalaris for maximum growth differs from that of ryegrass in winter. Keywords growth rates, ryegrass, tall fescue, phalaris, defoliation height, defoliation frequency, climate