An investigation into the relative efficacy of herbicides for the control of Deschampsia flexuosa (L.) Trin. in woodland

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

Deschampsia flexuosa (wavy hair grass) is a commonly occurring calcifuge grass which can be detrimental to tree regeneration. In the work reported here, two experiments using pot-grown plants and one field experiment were set up to investigate the relative efficacy of various herbicides in controlling D. flexuosa.

Cycloxydim, glyphosate and imazapyr applied in the summer killed virtually all pot-grown plants of D. flexuosa within a year of treatment. Hexazinone and propyzamide were also effective at the recommended doses.  Mixture B enhanced the efficacy of several herbicide treatments but pre-spraying plant moisture stress had no effect on subsequent herbicide activity. Cycloxydim and imazapyr applied in spring or summer gave excellent long term control in the field.

It is concluded that if non chemical approaches such as canopy manipulation or cultivation fail to give adequate control of D. flexuosa and herbicide use becomes necessary to allow tree regeneration, then cycloxydim applied at 0.45 kg a.i. ha-1 appears to be an effective alternative to the use of more broad spectrum products, and gives very good tree tolerance. If herbicide use is required prior to tree establishment, glyphosate may be a cheaper option and will control a broader spectrum of weeds, although it is slightly less effective than cycloxydim on D. flexuosa.

Practical implications

  • Deschampsia flexuosa can kill and suppress young trees, preventing regeneration or restoration. Opening up a tree canopy to allow naturally regenerating seedlings to grow, also often allows D. flexuosa to rapidly swamp the site.
  • Complete cultivation can suppress D. flexuosa, but this is not always appropriate, and the grass rapidly re invades. Plastic mulches can give effective control, but are expensive (£3800+ per treated hectare).
  • Glyphosate (e.g. as Roundup Pro Biactive), used at rates of  5 litres per hectare, is a cheap (£60 per treated hectare), safe and effective site preparation treatment. However, after planting or natural regeneration, applications need to be carefully targeted to avoid damaging trees, which is not always practical.
  • Cycloxydim (e.g. as Laser), used at rates of 2.25 litres per hectare (plus the required adjuvant Actipron at 2% of final spray volume), is very effective at controlling pure stands of D. flexuosa. It can be safely used over all tree and herbaceous species, at a cost of around £100 per treated hectare.
  • Cycloxydim may be the best option after tree natural regeneration or planting, for pure stands of D. flexuosa. Glyphosate may be best option before planting or for mixed weed spectrums.
  • Detailed practical recommendations have been issued in a Forestry Commission Technical Paper (Willoughby and Clay, 1999).

References

Dixon, F.L., Clay, D.V. and Willoughby, I. (2005).  An investigation into the relative efficacy of herbicides for the control of Deschampsia flexuosa (L.) Trin. in woodland establishment. Forestry 78 (3) 229-238.

Willoughby, I. and Clay, D. (1999). Herbicide update. Forestry Commission Technical Paper 28. Forestry Commission , Edinburgh.

For further information

Or to obtain a copy of the papers, please contact the author.

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