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Should you Apply Boron to Flowering Canola
Canola and alfalfa are two field crops with the highest requirement for boron. Canola uptake is 0.3 – 0.5 lb/ac (60 bu/ac yield), alfalfa 0.3 lb/ac (4 t/ac yield) Tissue testing for boron can be useful as soil testing has not proved reliable. Organic matter usually supplies enough boron for most crops, perhaps except very low O.M., or coarse-textured soils. Boron assists in flowering, pollination, and aids in reducing flower blasting due to heat. Limited Ontario studies utilizing foliar boron at fungicide timing, show mixed results and indicate the best opportunity for payback is under dry weather with moderate crop stress.  Read More: https://bit.ly/3eAY0JN
Western Canada studies have generally not shown a response to soil or foliar Boron and caution about widespread use. One of the more recent foliar studies is by Sask Irrigation Crop Diversification Corporation: read their 2018 summary and cautions about applying boron here: IRDC 2018 Report
Growers most commonly make foliar applications at the early flower stage. Fungicide companies generally suggest that Boron applications should be made separately over concerns of reduced fungicide efficacy. Ontario growers have not reported any concerns with this practice. Always check the label, and contact your agronomy specialist for the latest recommendations