Uptake and dissipation of neonicotinoid residues in nectar and foliage of systemically treated woody landscape plants

Researchers simulated soil injection applications on Ilex x attenuata (Foster holly) and Clethra alnifolia (summersweet) of imidacloprid (IMD) and dinotefuran to determine residue levels in leaves and nectar during the following bloom. Test groups included plants treated in summer (early post bloom), the fall (post bloom), and the spring (pre bloom). Neonicotinoid label rates for soil application to woody landscape plants are much greater on a per-plant basis than label rates in field crops. Nectar residues from label rate soil applications completed in fall and spring met or exceeded levels linked with harm to honey bee colonies. IMD levels ranged from 166 –515 ng/g (ppb); dinotefuran ranged from 70 – 1235 ng/g. IMD applications in the summer (early post bloom) did not cause nectar residue levels considered of concern to researchers (8 -31 ppb). Yet, it is worth noting that the levels of IMD in nectar from the summer applications are linked with some sublethal effects. Summertime post bloom applications of dinotefuran still showed nectar residue levels of concern the following year (235 – 1191 ppb). The second year of bloom after application showed a dramatic drop in residue levels for both chemicals. The researchers also looked at residues in foliage. IMD levels in Ilex leaves were between 28 and 90 times higher than in nectar. IMD levels were approx. 50 fold higher in Clethra. Dinotefuran residue in foliage was higher than for nectar (for Ilex range was from 4751 – 6287 ppb).  The researchers concluded that use of these products on woody bee-attractive landscape plants attractive poses a risk to pollinators even if label directions and bee precaution language are followed. The authors recommended avoiding the use of IMD or dinotefuran on bee-attractive trees and shrubs unless there is no other way to prevent significant pest damage.