Evaluation of fungicides for potential growth regulating properties on sorghum

Fungicidal compounds such as triazoles and strobilurins have been shown to have plant growth regulating properties leading to, amongst others, delayed senescence or increased yield. The aim of the current study was to evaluate the merit of the growth regulating properties of fungicides under South African production conditions on sorghum yield. Three split-plot trials were planted during 2013/14 and 2014/15 respectively (Greytown, Potchefstroom and Standerton). Eleven fungicide treatments (main plots) consisted of two fungicides (azoxystrobin/difenoconazole and epoxiconazole/pyraclostrobin) applied at 6 weeks, 6 & 8 weeks, 8 weeks, 8 & 10 weeks and 10 weeks after planting and an untreated control, replicated three times. Four cultivars were included as sub-plots. Leaf blight severity, percentage leaf senescence, plant biomass at harvest as well as yield were determined. Leaf blight severity in all trials was sufficiently low (<16%) to evaluate the growth regulating properties of the fungicides tested. During 2013/14 fungicide application resulted in delayed senescence at Greytown, but this effect was not observed at Potchefstroom or Standerton. Biomass was reduced by 20.3 and 24.3% with 10 week azoxystrobin/difenoconazole and 6 & 8 week epoxiconazole/pyraclostrobin applications respectively, in Potchefstroom relative to the control. Biomass was not affected at the other localities. Yield response to the various treatments during 2013/14 differed between localities, with azoxystrobin/difenoconazole treatment applied at 8 & 10 weeks resulting in a significant yield increase of 33.6% compared to the control at Standerton. During 2014/15 fungicide applications had no effect on senescence, plant mass or yield. Results indicated that fungicide application could not be relied upon to reduce the rate of senescence or stimulate yield sufficiently to warrant prophylactic fungicide applications with the expectation of financial gain in the absence of foliar diseases.