LATE season fungicide application can suppress weather-induced saprophytic fungal growth in oaten hay windrows.
That's according to research conducted between 2019 and 2021 as part of the National Hay Agronomy project, which is a collaboration between the Department of Primary Industries and Regional Development (DPIRD) and AgVictoria
Saprophytic fungi develop on the windrow following rainfall events, during the curing process, and these saprophytes feed on the dead or decaying leaf material, subsequently reducing the visual quality of the hay and its suitability for export markets.
In turn, this can affect the potential economic returns for growers.
DPIRD research scientist Kylie Chambers said anecdotal evidence had previously suggested late season applications of strobilurin fungicides could reduce saprophytic growth and increase green leaf retention in the windrow, therefore improving hay visual quality.
Over three seasons, trials were conducted in WA and Victoria with strobilurin (Qol group 11) and triazole (DMI group 3) based fungicides applied at either seven, 21 or 28 days prior to hay cutting.
Plots were swathed at Z71, the recommended growth stage for optimum hay quality, windrowed and weathered for up to 45 days to allow saprophyte colonisation.
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"We found that strobilurin fungicides reduced the level of saprophytic growth in the windrows by 55 to 85 per cent and had larger and more consistent effects than triazole fungicides," Dr Chambers said.
"Growers were also interested in the performance of the triazole fungicide propiconazole, as it is cheaper than other fungicides and has a shorter withholding period compared to the strobilurin-based fungicides (seven days versus 21 days).
"However, while propiconazole applied at seven days prior to cutting significantly reduced saprophytic growth, strobilurin-based fungicides applied at 21 or 28 days before swathing significantly outperformed the triazole fungicides."
The results indicated it may be better to spray earlier in the season to get both effective foliar disease control and potential suppression of saprophytes in the windrow with a single application.
However, the application of strobilurin fungicide 21 or 28 days prior to cutting offered similar levels of protection against saprophytic growth.
As hay crops can finish quicker than expected in some seasons, the earlier application timing can provide a buffer for growers to cut hay earlier than expected and still comply with withholding periods.
Dr Chambers found all the registered strobilurin-based fungicides used in the trials provided similar levels of saprophytic growth suppression .
"It is important to check the strobilurin fungicide you are applying in season is registered for management of the disease you are hoping to control," she said.
"Fungicides were observed to have the greatest effect on the surface of the windrow, where more saprophytic colonisation occurred.
"We believe this is most likely due to saprophytes preferring to feed on the sun-bleached tops of the windrow where there is more decaying leaf tissue and the fungicides had little to no effect inside the windrow."
The application of late-season fungicides did not impact on hay nutritional quality or affect the overall greenness of the hay, either at cutting or in the windrow.
However, the difference in saprophytic growth could impact on overall hay visual quality if the bleached portion made up a high percentage of the windrow and result in a downgrade of hay quality and value for the producer.
It is important that fungicide groups are rotated and are only applied to address foliar disease risks at the time of application.
Following label recommendations for application rates and withholding periods is critical to avoid the risk of chemical residues in hay and potentially jeopardising export markets.
