• Natural products as herbicides

Natural products as herbicides for tree establishment

Summary (from the scientific paper: Clay et al., 2005)

The selectivity and efficacy of the foliar-acting natural product herbicides bilanaphos and citronella oil were tested in comparison with glufosinate ammonium:

  • When applied to tree base foliage of 10 species of broadleaved and coniferous trees in May or June they caused contact damage to the sprayed area only.
  • Overall application of bilanaphos and glufosinate ammonium and directed application of citronella oil to dormant trees in winter had no adverse effect on broadleaved trees but severely damaged conifer species.
  • When sprayed on five species of actively growing herbaceous perennial weeds in May, bilanaphos gave good short-term control of Senecio jacobaea (ragwort) and perennial grasses and glufosinate ammonium of Rumex obtusifolius (dock).
  • Citronella oil at a high dose largely killed foliage of all species within 1 day of application but most species re-grew strongly. S. jacobaea was the most susceptible species, with good control 2 months after application of the higher dose.

Both these natural product herbicides are of potential use for tree establishment but costs of development and registration may be prohibitive. Public perceptions have not yet been assessed.

Practical implications

  • Pesticides synthesised from naturally occurring chemicals may be an alternative to artificially synthesised compounds.
  • Bilanaphos is a fermentation by-product, and has similar properties to the synthetic pesticide glufosinate ammonium. It  is not currently registered for use in the UK.
  • Citronella oil is a plant extract, approved for use on grassland and non crop areas, and marketed in the UK as Barrier Biotech.
  • Citronella oil gives good control of ragwort, but is relatively expensive and requires high product rates.
  • Natural products are not necessarily less toxic than other pesticides.
  • The attitude of the public, and of governmental organisations to natural product herbicides needs to be assessed for any further development work takes place.
  • Practical guidance has been issued in a Forestry and British Timber article (Willoughby and Clay, 2002).


Clay, D.V., Dixon, F.L. and Willoughby, I. (2005). Natural products as herbicides for tree establishment. Forestry 78 (1), 1-9.

Willoughby, I. and Clay, D.V. (2002). Natural product herbicides in forestry : what are the prospects? Forestry and British Timber 31 (2), 22-25.

For further information

Or for a free copy of the papers, please contact the author.

Ian Willoughby
Email: ian.willoughby@forestry.gsi.gov.uk