Evaluation of the effect of plant growth regulators and fungicides on light interception, growth and yield of oilseed rape

Abstract

In 1996, four triazole-based fungicides and three conventional plant growth regulators were tested for effects on canopy structure, crop growth and seed yield of autumn-sown oilseed rape at ADAS Rosemaund and The University of Nottingham. At both sites, the fungicide Folicur, applied during early stem extension, reduced stem growth and lodging, increased canopy erectness and significantly increased the seed yield on crop samples harvested by hand prior to combining.

These increases resulted from improvements in pod and seed retention particularly in the lower half of the pod layer. There were also important increases in harvest index showing that Folicur had improved the pattern of biomass distribution. when harvested later, by plot combine, there was no significant difference in yield between the control and Folicur treatments.

It appears most likely that the plots treated with Folicur ripened earlier and shed a larger proportion of seed in the period between the hand harvest and combining. There was no evidence that either the proprietary growth regulators or other fungicides tested were effecting combine yields at either site. At ADAS Rosemaund in the hand harvested samples there was a small yield increase of about 0.4 t ha-1 (not statistically significant) from both Opus and Cerone. Although not significant in this case, this may be worthy of further investigation.

This project has provided direct evidence that, in the absence of effects on disease, some fungicides can improve yield by increasing the productivity of the pods lower in the pod canopy. Folicur increased light penetration through the canopy but the magnitude of this improvement was small and unlikely to account for all of increase in seed yield.

The reduction in stem growth appeared to limit pod number and in so doing, may have increased the assimilate available for the earlier initiated pods at the base of the crop, and thus improved initial seed set. Before these potentially valuable effects from fungicides with growth regulating properties can be reliably incorporated into systems of rape production, the effects on canopy manipulation must be more fully investigated to identify the underlying physiological mechanisms, and thus identify crops likely to respond.