Hay discolouration due to saprophytic fungal growth is a major concern for export oaten hay producers as it reduces visual quality, suitability for export markets, and economic returns by approximately $150 per tonne. Saprophytic fungi thrive on senescing or dead tissue, particularly during hay curing, which creates an ideal environment for colonisation, especially when it coincides with rainfall events.
In 2018, agronomists and growers observed that late season strobilurin fungicide applications in oats appeared to increase leaf greenness and reduce saprophytic growth. This evidence of increased economics through fungicides led to a significant rise in sales in high-risk areas. Initial trials determined that these fungicide applications reduced saprophytic damage but there was no impact on leaf greeness or nutritional quality.
As a result, many growers began applying fungicides as late as possible, at the withholding period (WHP) to minimise saprophytic damage. This change in practice reduced flexibility in cutting times, increasing the risk of reduced nutritional quality (due to cutting hay at a later growth stage) and the potential of exceeding maximum residue limits (MRL’s)hay was cut early, which would jeopardise the export hay market.
Eight field trials across Victoria and Western Australia were conducted between 2019 and 2024 to investigate the suppression effect of strobilurin, SDHI and triazole fungicides on colonisation by saprophytic fungi. Additionally, the trials aimed to determine the earliest fungicide application timing that would provide effective saprophytic control while ensuring MRLs in oaten hay were not exceeded. Commonly grown varieties Brusher (Victoria) and Carrolup (Western Australia) were grown and fungicides applied at various timepoints. Plots were swathed, windrowed and weathered for up to 45 days to allow for saprophyte colonisation. The percentage leaf area affected by saprophytic growth was assessed from subsampled plants from the top (bleached) and the sub surface (green) areas of the windrows. Nutritional quality parameters were determined for subsamples using NIR. Physical quality parameters were determined for subsamples using NIR, Minolta colour measurements, and determining leaf area affected by fungal disease (predominantly Septoria and red leather leaf).
Results showed that strobilurin fungicide application significantly reduced saprophytic growth in all trials, outperforming triazoles. The greatest effect was observed on the surface of the windrow, while no effect was observed on the sub-surface saprophytic growth. Importantly, fungicide application and subsequent saprophyte reduction did not affect the “greeness” or nutritional quality parameters of the hay.
This research also showed that applying the strobilurin fungicide 1-2 weeks earlier than the WHP achieved similar level of saprophyte reduction while offering greater flexibility in cutting times, reducing disease levels (when present) and lowering the risk of exceeding export MRLs. These findings suggest that strobilurin fungicides can be an effective tool for saprophytic management in export oaten hay production.