N,N-diethyl-meta-toluamide (DEET) exposure produces rapid and permanent damage in turfgrass

Despite anecdotal evidence that suggests bug sprays containing N,N-diethyl-meta-toluamide (DEET) damage turfgrasses, there is no peer-reviewed research investigating this in detail. The aims of the present study were to determine whether it is the DEET or the carrier solvent in bug sprays, ethanol, that damages turfgrasses, quantify the level of damage, and establish whether turfgrasses treated with DEET would recover in both indoor and outdoor environments. In a controlled, indoor environment, directly spraying DEET solutions on perennial ryegrass damaged leaves in a dose-dependent manner with an LD50 of 9.7%. Direct spraying of DEET solutions also damaged both perennial ryegrass and bentgrass in two separate, outdoor experiments, performed one year apart. Turfgrasses that died due to DEET exposure did not recover even up to 30 days after treatment in indoor experiments. Furthermore, an untargeted metabolomics analysis revealed significant changes in the metabolomes of DEET-treated perennial ryegrass within one hour of DEET application, prior to observable phenotypic effects. This report is the first rigorous demonstration that the DEET in bug spray directly damages turfgrass.