A multi-technique approach for nanoherbicide tracking: uptake and translocation pathways of the metribuzin nanocarrier in weed plants

Understanding the strategies of delivering active ingredients with nanoparticles to plant species is crucial to implement a safe-by-design approach for pesticides. Here, we used metribuzin (MTZ) as a study model to understand the plant uptake and distribution pathways of polymeric nanocarriers. We investigated the weed-control efficacy, uptake, internalization, and distribution of the (nano) herbicide MTZ in Amaranthus viridis (C4 species) and Bidens pilosa (C3 species) after soil and foliar application. A radiolabeled herbicide and a fluorescent probe were used as complementary tools to track both MTZ and nanoparticles in plants. The weed-control results indicated significant dose reductions with MTZ nanoencapsulation (from 1/2 to 10-fold doses). Root uptake was an efficient pathway for A. viridis and the B. pilosa entry of nanoMTZ occurred preferentially in the stomata and was internalized in leaf mesophyll cells. No differences in herbicide uptake were observed in the soil, and the nanoMTZ distribution was 1.3-1.5 lower than MTZ. After foliar application, nanoMTZ was absorbed 2.5 times more than MTZ in A. viridis and was similar in B. pilosa. NPs were concentrated in the vascular cells after soil application and in the stomata entrance after foliar application. For B. pilosa, the internalization in the leaf mesophyll was more evident than that in A. viridis. Our findings indicated that consideration of the target weed species and application mode will increase the efficacy of control using nanoformulations.