Translocation of the neonicotinoid seed treatment clothianidin in maize

This field study examined the movement of neonicotinoid seed treatments (clothianidin) into corn plant tissues. It sought to define the amount of clothianidin taken up by the plants and the pest management window for seed treatments. Clothianidin was applied to seeds at two treatment rates along with three fungicides. Some contamination was expected in the untreated controls because treated seed had been planted in the fields in years prior to the study, and they were in close proximity to other fields planted with treated seed during the study. A maximum of 1.5% of the clothianidin applied to treated seed was translocated into plant tissues. Based on the decay of clothianidin in the tissues and an assumption that low levels of clothianidin would provide a pest management benefit, the authors considered pest protection for the shoots to exist for 34 days post planting and for the roots to last for 34-47 days post planting depending on the concentration of clothianidin applied. These protection windows may not overlap with primary corn pests in the US. There was a potential of about 20 days of overlap with western corn rootworm larvae, which are primarily controlled by Bt crop varieties. Some secondary corn pests may be partially controlled by clothianidin seed treatments, including wireworm, seed-corn maggot, and white grub, but there are no published accounts of the amount of clothianidin needed to control these pests and their outbreaks are typically sporadic. The authors found no statistical differences in stand count, root ratings, or yield between the corn grown from treated and untreated seed. Since such a small quantity is translocated into the plant, the authors recommend that determining the environmental fate of the remaining ~98% of clothianidin applied to seeds should be an area of further research, and may explain the frequent detections of neonicotinoids in non-target areas.