Greenhouse production practices for making flowers safer for yard and garden pollinators

Nursery and greenhouse growers need guidelines for pest management strategies that minimize the impact of insecticides applied during production on pollinators visiting flowering plants after they are purchased and planted in the yard and garden.  Two practices that may be detrimental to pollinators are: (1) a soil drench of imidacloprid applied to hanging baskets just before they are hung, and (2) foliar sprays of an insecticide made during the last four weeks before shipping.  These practices were investigated in experiments that determined the impact of soil drenches on bumble bees and measured dislodgable insecticide residue on the flowers of sprayed plants one week after shipping.  In 2014 bumble colonies produced a similar number of workers after a 3-week exposure period to plants drenched with imidacloprid or water.  However queen production was poor in both treatments.  Results of the dislodgable residue study indicates that in order to protect pollinators greenhouse and nursery flowers should not be sprayed the last 2 weeks before shipping.  These experiments will be repeated in 2015.