Many Ontario canola producers tank mix boron with a preventative white mould fungicide and apply it at 20-50% bloom. We took a closer look at whether foliar boron reduces flower abortion or improves yield.
The simple answer
Published research from across Canada does not show a consistent positive yield response to foliar boron applications, when there is not a boron deficiency. A positive return on investment for foliar boron applications during flowering is most likely if boron supply is limited by dry soil conditions, and the boron is tank mixed with a planned preventative white mould fungicide application.
A little more information
Canola flowers have a higher boron concentration than other plant parts and may be more sensitive to low boron supply. Boron is taken up through mass flow of water from roots through the xylem. Boron cannot be redistributed from foliage to flowers; a continuous supply of boron is required for canola growth. Dry soil conditions reduce mineralization of boron from soil organic matter. Even if boron fertilizer has been soil-applied, dry conditions limit boron uptake and transient boron deficiencies may occur.
Boron deficiency symptoms are rare and generally not a factor in the application of foliar boron in Ontario. Because of the low cost of boron products, the high boron requirement of canola relative to other field crops, and perceived benefits of boron in pollination, most spring canola growers in Ontario tank-mix boron with their preventative white mould fungicide. It is often stated that boron provides protection against flower abortion during hot conditions, but this is not supported in scientific literature, although some data to suggest this was generated in an unpublished trial conducted at University of Guelph. It is more likely that benefits of foliar boron are realized on Ontario farms because of lack of boron uptake by roots during dry conditions at flowering.
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