Effects of the herbicide dicamba on nontarget plants and pollinator visitation

Abstract

Nearly 80% of all pesticides applied to row crops are herbicides, and these applications pose potentially significant ecotoxicological risks to nontarget plants and associated pollinators. In response to the widespread occurrence of weed species resistant to glyphosate, biotechnology companies have developed crops resistant to the synthetic-auxin herbicides dicamba and 2,4-dichlorophenoxyacetic acid (2,4-D); and once commercialized, adoption of these crops is likely to change herbicide-use patterns. Despite current limited use, dicamba and 2,4-D are often responsible for injury to nontarget plants; but effects of these herbicides on insect communities are poorly understood. To understand the influence of dicamba on pollinators, the authors applied several sublethal, drift-level rates of dicamba to alfalfa (Medicago sativa L.) and Eupatorium perfoliatum L. and evaluated plant flowering and floral visitation by pollinators. The authors found that dicamba doses simulating particle drift (≈1% of the field application rate) delayed onset of flowering and reduced the number of flowers of each plant species; however, plants that did flower produced similar-quality pollen in terms of protein concentrations. Further, plants affected by particle drift rates were visited less often by pollinators. Because plants exposed to sublethal levels of dicamba may produce fewer floral resources and be less frequently visited by pollinators, use of dicamba or other synthetic-auxin herbicides with widespread planting of herbicide-resistant crops will need to be carefully stewarded to prevent potential disturbances of plant and beneficial insect communities in agricultural landscapes.

Ecological intensification to mitigate impacts of conventional intensive land use on pollinators and pollination

“…; Hanley & Wilkins ; Bohnenblust et al . ). Moreover, some herbicides can be directly toxic to larval stages of pollinators (Hahn et al .…”

“…; Bohnenblust et al . ). Their widespread and expanding cultivation could represent a threat to pollinators, increase pollination deficits and yield reduction in insect‐dependent crops, but this needs further study.…”

Comparative Assessment of Vegetative and Reproductive Terrestrial Plant Species Endpoints from Exposure to Herbicides and Potential Environmental Implications: A Review

“…Finally there is some information indicating that the growth stage at which the plant is exposed may play an important role (e.g., Boutin and Rogers ; Gilreath and Chase ; Gilreath et al ; Strandberg et al ; Griffin et al ). For our separate investigation of the effect the application timing may have on the sensitivity, see Supplemental Data H, which also includes data from Bohnenblust et al (), Nelemans et al (), and Olszyk et al ().…”

Plant reproduction is altered by simulated herbicide drift to constructed plant communities

“…The herbicide effects on reproduction were associated with reduced occurrence in plots and biomass for some species . Another example of field research was by Bohnenblust et al , who reported that 0.01× f.a.r. of dicamba reduced the number of flowers in Medicago sativa L. grown in field plots and Eupatorium perfoliatum L. grown in pots.…”