Systemic insecticides can contaminate nectar or pollen. Some pesticides have little effect on bees. Some have little residual effect, so can be sprayed when bees are not active. Many are highly toxic to bees. Toxicity First a few generalities.
Dusts are usually more hazardous than sprays.
Granular pesticides seem to present little hazard. Fungicides and herbicides are relatively non-toxic to bees, if used as labeled. Insecticidal soap has little effect on bees, even when sprayed directly, since the bee's heavy cuticle is not easily penetrated by the fatty acids. Cultural Practices A concern for bees may mean adjusting some of our spray practices. In the spring, before our roses begin to bloom, morning spraying poses little danger to foraging bees, unless spray drifts onto other spring-blooming plants being visited by bees.