Spray application methods to maximize Sclerotinia control in canola with foliar fungicide
Vinclozolin (Ronilan) and benomyl (Benlate) fungicides were applied to canola with 5 application methods to determine the impact of nozzle type and pressure on Sclerotinia stem rot suppression over 3 seasons in north-east Saskatchewan. A spray deposition study was conducted under controlled conditions, which showed that the majority of spray was intercepted by the top third of the canola canopy for all application systems, with a slight increase in the amount deposited on the upper flowers with elevated spray pressure. Flowers and buds retained nearly 20% of the total applied spray dose, and leaves retained most of the remainder. Stems retained a very minor proportion of the applied dose. Coarser sprays delivered more of their dose in the target area, but had lower retention values on flowers and buds than the finer sprays. In field experiments fungicide effectiveness varied with environmental conditions each season but both products were generally equally effective in 1998 and 2000, reducing stem rot incidence and increasing yield over that of untreated plots. In 1999 neither fungicide was effective for Sclerotinia control likely due to the prevailing environment that was conducive to heavy disease development. Overall, conventional flat fan nozzles (TeeJet XR) and low-drift venturi nozzles (Greenleaf TurboDrop) were equally effective at reducing stem rot incidence. There was a trend to improved stem rot control and increased yield for each nozzle when operated at elevated pressure. Based on these results, venturi nozzle technology is appropriate for use with foliar fungicides for Sclerotinia stem rot control in canola provided pressures are adjusted to optimize nozzle performance.
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