Can Ontario winter wheat growers mix ammonium thiosulphate (ATS) with herbicides and fungicides to address sulphur deficiency symptoms or should they apply it separately with streamer nozzles?
That’s a question Mike Cowbrough and Joanna Follings wanted to answer with 2018 research plots. The Ontario Ministry of Agriculture, Food and Rural Affairs weed specialist and cereals specialist, respectively, take us on a tour of their research plot at Woodstock, Ont., and review their findings in this Wheat School episode.
With reductions in atmospheric sulphur deposits, Ontario research has found significant yield responses (10-14 bu/acre) to sulphur applied on some fields, while others have shown little or no response, especially where manure had been applied. Of all the Ontario trial sites, 59% were responsive, with an average response of 3.8 bu/ac, while across all sites the average response was 2 bu/ac.
Ideally, sulphur is applied as ATS with 28% urea ammonium nitrate (UAN) at the tillering stages in the early part of spring. But what happens when a grower is seeing deficiency symptoms and would like to address them at the same time by applying a herbicide or fungicide (or perhaps both)? Under this circumstance, the grower needs to consider four key factors:
- ATS applied with nozzles that are used for pesticide applications (and therefore create finer droplets) resulted in increased visual crop injury
Streamer nozzles would dramatically decrease the amount of foliar burn that is caused when ATS is applied with a nozzle used for applying pesticides.
- Mixing ATS with a herbicide and/or a fungicide increases the risk of crop injury.
A recent paper by University of Guelph’s Dr. Dave Hooker and his colleagues showed that the addition of ATS increased visual injury in wheat and was greatest in a three-way herbicide + fungicide + ATS tank-mix. (See Table 1)
- A third factor to consider is whether increasing water volumes decrease the risk of crop injury with ATS (you are diluting the concentration of ATS in the carrier volume).
During the 2018 field seasons, Cowbrough and Follings evaluated ATS tank-mixes with herbicides at two different carrier volumes. The first carrier volume was a 1:1 ratio of ATS to water (100 L/ha or 10 gal/ac total carrier volume) while the second was a 1:3 ratio of ATS to water (200 L/ha or 20 gal/ac total carrier volume).
The researchers observed a similar increase in crop injury when ATS was tank-mixed with herbicide as noted in the Hooker research. However, they did not observe any visual differences in foliar injury when using different carrier volumes. They speculate that even though they were diluting the amount of ATS with a higher carrier volume when the ATS-to-water ratio was 1:3 compared to 1:1, they were also increasing the foliar coverage on the cereal leaves with the higher carrier volume, perhaps negating any benefit of dilution. (See final conclusions below the video.)
Cowbrough and Follings note that it’s important to remember that this was only one trial conducted in one year, so the sample size is very small, but there was no evidence in this trial that increased carrier volume decreased foliar leaf burn.
- Injury from ATS does not cause yield loss.
In their 2018 study, Cowbrough and Follings found no difference in winter wheat yield across all treatments, regardless of amount of foliar injury, which in some instances reached 15% visual injury. It should be noted that injury from ATS seems to be most apparent in the first three to five days after application but after 14 days it has virtually disappeared. The Hooker study also found that despite significant crop injury, the injury was transient and there was no evidence that grain yield was adversely affected.