I. Occurrence and evidence for the use of nitrogen as a control measure

Abstract

The occurrence of blind seed disease of ryegrass in New Zealand has declined over the last 20 years. During 1948-1960, more than 70% of ryegrass seed samples tested were infected by the pathogen, and mean infection levels per seed line, although fluctuating according to the season, averaged 12%. Levels of over 20% were recorded in 1950, 1952, and 1958. Since then, both the percentage of infected samples and the mean infection level per sample have declined, and during [1976][1977][1978], 27% of seed samples tested carried the pathogen, with a mean infection level per seed line of 4.0%. During this time, the only major change in management technique for ryegrass seed production has been the use ofnitrogenous fertilisers to boost yields. Unpublished New Zealand work and the literature on blind seed disease and nitrogen is reviewed, and a link between the increasing use of nitrogenous fertilisers by New Zealand seed producers and the decrease in the occurrence of blind seed disease is proposed.

New Zealand's seed health

“…Most common were F. avenaceum > M. nivale > F. graminearu > F. culmorum > F. poae. This survey is noteworthy for two reasons: firstly, the results are very similar to those reported by Hampton (1980), illustrating the fact that the systemic seed treatments in use for the last 20 years do not effectively control Fusarium spp. (indeed, the incidence of Fusarium spp.…”

“…The committee continued to meet until the late 1950s. Control strategies investigated included breeding for disease resistance, fungicide seed treatment, and fertiliser management (see Hampton & Scott 1980), but none were successful as between 1948 and 1960, 70% of ryegrass seed samples were positive for blind seed disease, with an average infection level of 12% (Hampton & Scott 1980).…”

“…The pre-harvest testing of ryegrass seeds for the presence of blind seed disease had peaked in the early 1950s (over 3,000 samples were tested in 1952), but then fell rapidly during the 1960s to the extent that pre-harvest testing was discontinued (Scott 1974). During 1976During -1978 of seed lots carried the pathogen, with a mean infection level per seed lot of 4% (Hampton & Scott 1980). Gaunt et al (1978) reported the presence of Ascochyta fabae, the causal agent of leaf, stem and pod spot broad and field beans (Vicia faba) in Canterbury and estimated yield losses of 15% in many crops.…”

“…After a review of 30 years of testing data, Hampton and Scott (1980) concluded that blind seed disease was decreasing in importance, and proposed the hypothesis that because the spring application of urea can significantly reduce blind seed disease (Hampton & Scott 1981;Hampton 1987), the increasing use of nitrogenous fertilisers for herbage seed production was a major contributor to the decline in importance of the pathogen. However, while in most seasons from 1980-1990 only low levels of blind seed disease were recorded, there were major problems in the following three seasons (Hampton 1994).…”

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

“…Hampton & Scott (1980) reviewed the literature and suggested that the explanations previously suggested for the link between a reduction in blind seed disease and high fertility were not satisfactory, and that two other possibilities, originally suggested by Wilson et at. (1945), should be investigated: viz, that the use ofnitrogenous fertilisers altered the soil reaction and hence had some effect on apothecial development; that a vigorously growing crop may be physiologically less susceptible to attack than a poor thin one.…”