First and foremost, when it comes to protecting pollinators, one must read and follow all pesticide label instructions. Some products are highly toxic to bees and will clearly state on the label “this product is highly toxic to bees exposed to direct treatment or residues on blooming crops or weeds.”
So, as a rule, it is recommended not to spray insecticides just before or during bloom. However, if you find it necessary to spray for pests such as in a blooming canola field, try to spray later in the evening hours or at night when bees are less active, or during early morning hours before the bees start to actively forage. Pesticides that have had time to completely dry on the plant may be less toxic to foraging bees. Also consider making a perimeter application rather than the entire field if the heaviest pest pressure occurs on field borders.
If beekeepers have brought in hives (Fig. 1), it may be advisable to remove bee shelters during and for 2-3 days following application and making sure to avoid any direct application to such structures. For more information on this topic, check out WSU Extension Fact Sheet Pollination and Protecting Bees and Other Pollinators (FS174E).