To cite targets in publications use:

Landau WM (2021). “The targets R package: a dynamic Make-like function-oriented pipeline toolkit for reproducibility and high-performance computing.” Journal of Open Source Software, 6(57), 2959. https://doi.org/10.21105/joss.02959.

Corresponding BibTeX entry:

  @Article{,
    title = {The targets R package: a dynamic Make-like
      function-oriented pipeline toolkit for reproducibility and
      high-performance computing},
    author = {William Michael Landau},
    journal = {Journal of Open Source Software},
    year = {2021},
    volume = {6},
    number = {57},
    pages = {2959},
    url = {https://doi.org/10.21105/joss.02959},
  }