Effects of light leaf spot (Pyrenopeziza brassicae) on yield of winter oilseed rape (Brassica napus)

Abstract

The relationship between development of light leaf spot and yield loss in winter oilseed rape was analysed, initially using data from three experiments at sites near Aberdeen in Scotland in the seasons 1991/92, 1992/93 and 1993/94, respectively. Over the three seasons, single-point models relating yield to Light leaf spot incidence (% plants with leaves with light leaf spot) at GS 3.3 (flower buds visible) generally accounted for more of the variance than single-point models at earlier or later growth stages. Only in 1992/93, when a severe light leaf spot epidemic developed on leaves early in the season, did the single-point model for disease severity on leaves at GS 3.5/4.0 account for more of the variance than that for disease incidence at GS 3.3. In 1991/92 and 1992/3, when reasonably severe epidemics developed on stems, the single-point model for light leaf spot incidence (stems) at GS 6.3 accounted for as much of the variance. Two-point (disease severity at GS 3.3 and GS 4.0) and AUDPC models (disease incidence/severity) accounted for more of the variance than the single-point model based on disease incidence at GS 3.3 in 1992/93 but not in the other two seasons. Therefore, a simple model using the light leaf spot incidence at GS 3.3 (x) as the explanatory variable was selected as a predictive model to estimate % yield loss (y(r)): y(r) = 0.32x - 0.57. This model fitted all three data sets from Scotland. When data sets from Rothamsted, Rosemaund and Thurloxton in England were used to test it, this single-point predictive model generally fitted the data well, except when yield loss was clearly not related to occurrence of light leaf spot. However, the regression lines relating observed yield loss to light leaf spot incidence at GS 3.3 often had smaller slopes than the line produced by the model based on Scottish data

Predicting light leaf spot (Pyrenopeziza brassicae) risk on winter oilseed rape (Brassica napus) in England and Wales, using survey, weather and crop information

“…Accurate predictions of the risk of severe epidemics are therefore needed to guide decisions about fungicide applications. Su et al . (1998) demonstrated a relationship between incidence (percentage of plants affected) of light leaf spot at growth stage (GS) 3·3 (Sylvester‐Bradley & Makepeace, 1985) in spring and percentage yield loss at harvest, with approximately 10% yield loss for each additional 30% plants affected by light leaf spot.…”

Modelling the progress of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) in relation to leaf wetness and temperature

“…Light leaf spot, caused by the pathogen Pyrenopeziza brassicae , is one of the two most important diseases of winter oilseed rape in the UK (Su et al ., 1998). Yield losses of up to £40 million per annum have been estimated in recent years (Gladders, 1998).…”

The impact of climate change on disease constraints on production of oilseed rape

“…Regression analyses of position and parallelism had shown that the data for the two growing seasons were fitted best by a single line rather than two lines, and other tests had shown that they were fitted better by a linear relationship than a curve (polynomial equation logit(p) = log(p/1-p)(data were logit-transformed to normalise the variance), T s was mean temperature in the previous summer (July/August) before the crop was sown and R w mean monthly rainfall during winter (December to February) when the crop was at the rosette growth stage. The predictions of light leaf spot incidence for each site and scenario were then used to calculate predicted yield loss for each site and scenario using a modified version of the yield loss model derived by Su et al (1998).…”