Severe bee poisoning most often results from spraying insecticides directly on flowering plants, either the crop itself or flowering weeds within its margins. In Nebraska, insecticide applications are generally not recommended on blooming crops. An exception would be treatments applied to pollinating corn for second generation European corn borer. Other materials should always be selected at this time. Relative Toxicity of the Chemical.
Pesticides vary in their toxicity to honey bees.
Products such as Counter, Di-Syston, Dyfonate, Lorsban, Sevin XLR and Thimet are only moderately toxic to bees and can be used on many crops when bees are not actively foraging, generally in late evening. One group of insecticides highly toxic to honey bees cannot be applied to blooming crops when bees are present without causing serious injury to colonies. Damage caused by these materials is much less serious to honey bees than the others listed in this category. Their selection is preferable if honey bees are a factor. Choice of Formulation.