Response of winter wheat to herbicide plus fungicide plus ammonium thiosulphate tank-mixes

Abstract

A study was conducted at six field sites near Exeter and Ridgetown, ON, over a 3 yr period (2014, 2015, and 2016) to determine the effect of ammonium thiosulphate (ATS), various fungicides (azoxystrobin/propiconazole, trifloxystrobin/prothioconazole, or pyraclostrobin/metconazole), and various herbicides (bromoxynil/MCPA, thifensulfuron/tribenuron + MCPA, pyrasulfotole/bromoxynil, or 2,4-D/dichlorprop) applied alone and in tank-mix combinations on winter wheat crop injury and grain yield. The treatments were applied using Hypro ULD120-02 flat-fan nozzles around Zadoks growth stage 30. The herbicides and fungicides caused <0.6% leaf injury when ATS was not added to the tank-mix. When averaged across fungicides in ATS tank-mixes, leaf injury 1 wk after treatment application was 3.5% to 3.7% with thifensulfuron/tribenuron and dichlorprop-P/2,4-D herbicides and 5.1% to 5.8% injury with bromoxynil/MCPA and thifensulfuron/tribenuron herbicides. On the three field sites with the highest leaf injury, a fungicide–ATS tank-mix increased injury to 4.5% averaged across fungicides and to 4.3% with a herbicide–ATS tank-mix averaged across herbicides. Three-way tank-mixes of herbicide–fungicide–ATS caused the highest injury (7.1%). Despite significant crop injury 1 WAA with some tank-mixes, there was no evidence that grain yields were adversely affected. This study shows that the co-application of a three-way tank-mix of ATS with fungicides (azoxystrobin/propiconazole, trifloxystrobin/prothioconazole, or pyraclostrobin/metconazole) and herbicides (bromoxynil/MCPA, thifensulfuron/tribenuron + MCPA, pyrasulfotole/bromoxynil, or dichlorprop-P/2,4-D) has the potential to cause considerable injury in winter wheat under some environmental conditions in Ontario, but the effect seems transient, with no grain yield reductions detected.