II. Nitrogen fertiliser: Effect on incidence, and possible mode of action

Abstract

Application of urea at rates from 56 to 256 kg/ha either in spring or at ear emergence to ryegrass plots where blind seed inoculum (apothecia of Gloeotinia temulenta (Prill. and Del.) Wilson, Noble and Gray) was present significantly reduced blind seed infection and correspondingly increased germination of harvested seed in trials in 1972and 1978.In the 1978 trial, sulphate of ammonia at 56 and 112 kg/ha reduced the amount of blind seed, but not significantly. In laboratory and pot testing, urea directly suppressed apothecial formation, whereas sulphate of ammonia did not do so as effectively. In the 1972 field trial, inoculum (infected seed) was introduced before nitrogen treatments were applied, and although apothecial numbers were low, no differences in apothecial numbers between treatments could be determined. In the 1978trial inoculum (apothecia in petri dishes) was introduced after the nitrogen treatments. The results from this trial suggest nitrogen controls blind seed disease by changing toe physiological susceptibility of the plant to attack, rather than by directly affecting the pathogen.

Effect of nitrogen rate and time of application on seed yield in perennial ryegrass cv. Grasslands Nui

“…A reduction in blind seed infection as nitrogen application rates increase has been previously reported (Hampton & Scott 1980, 1981. In 1985, splitting the N application in the spring reduced the control offered by the urea, but whether this was because of application after spikelet initiation (Hampton & Scott 1981) or because the rate applied at spikelet initiation was correspondingly reduced, i.e., 33 or 50 g m-2 instead of 100 g m-2 , could not be determined.…”

“…In 1985, splitting the N application in the spring reduced the control offered by the urea, but whether this was because of application after spikelet initiation (Hampton & Scott 1981) or because the rate applied at spikelet initiation was correspondingly reduced, i.e., 33 or 50 g m-2 instead of 100 g m-2 , could not be determined. How urea reduces blind seed infection (Hampton & Scott 1980) in L. perenne remains to be determined.…”