Direct seeding is the process of sowing tree seed in its final growing position rather than transplanting nursery-grown stock to the site. Early research into direct seeding showed that depredation of seed by rodents and birds and variable seed viability often resulted in low germination rates. Seedlings that do germinate face competition from fast-growing weed species colonising the open site, which can reduce growth rates and survival significantly.
Weeds competing with a direct sown birch seedling
However, for certain species and site types, direct seeding offers a potential means of creating new broadleaved woodlands with better quality timber, rapid growth rates and a more natural appearance. The technique also has great potential for creating large woodlands linking existing areas of ancient semi natural woodland. Successful establishment can be achieved at a lower cost and reduced herbicide input than conventional methods, by making use of farm-scale techniques and machinery.
Successful application of the technique is currently confined to a range of some broadleaved species for new woodland creation, but research into its potential for restoration of plantations on ancient woodland sites, and for low-cost creation of native woodland habitats on felled upland plantation sites, is taking place.
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The selectivity and efficacy of the foliar-acting natural product herbicides bialaphos and citronella oil were tested in comparison with glufosinate ammonium:
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.
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.
Or for a free copy of the papers, please contact the author.
Ian Willoughby
Email: ian.willoughby@forestry.gsi.gov.uk
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.
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.
Or to obtain a copy of the papers, please contact the author.
Ian Willoughby
Email: ian.willoughby@forestry.gsi.gov.uk
The selective herbicide clopyralid is often used to control competing Cirsium arvense (creeping thistle) in newly planted woodlands. When applied as an overall spray at different dates in the spring (at 0.2 kg a.e. ha-1) to 10 tree species (below) it did not reduce survival and had little effect on growth:
However some species showed distortion of the youngest sprayed leaves or needles for several weeks after treatment, particularly F. excelsior, L. kaempferi and P. x canadensis. Sequential applications of clopyralid (first at 0.1 kg a.e. ha-1 followed by 0.2 kg a.e. ha-1 after 3 weeks), which are often required to control C. arvense, did not lead to increased leaf damage or growth reduction. Mixtures of clopyralid with selective graminicides (cycloxydim at 0.45 kg a.i. ha-1; fluazifop-p-butyl at 0.38 kg a.i. ha-1; propaquizafop at 0.15 kg a.i. ha-1) did not cause significant adverse effects on survival or growth of any species.
If herbicides are required to control mixed stands of susceptible problem weeds such as C. arvense and grasses which are overtopping young trees, these mixtures, applied as overall sprays, are less likely to cause damage to trees than attempts to use directed applications of broad spectrum foliar acting herbicides.
Dixon, F.L., Clay, D.V. and Willoughby, I. (2005 in press). The tolerance of young trees to applications of clopyralid alone and in mixture with other foliar acting herbicides. Forestry 78 (4) 353-364.
Willoughby, I. and Clay, D. (1999). Herbicide update. Forestry Commission Technical Paper 28. Forestry Commission, Edinburgh.
Willoughby, I. and Dewar, J. (1995). The use of herbicides in the forest. Forestry Commission Field Book 8. HMSO, London.
Or to obtain a copy of the papers, please contact the author.
Ian Willoughby
Email: ian.willoughby@forestry.gsi.gov.uk
A web-based system was developed to advise on the relative efficacy of different herbicides for mixes of weed and crop species at different times of the year in a forestry or farm forestry setting.
The system assumes that weed identification and impact assessment or prediction has already been accomplished and that there are no cost-effective non-chemical alternatives. The expert system produces a relative suitability index for each herbicide, as well as an English language discussion of the case.
Thomson, A.J. and Willoughby, I. (2004). A web-based expert system for advising on herbicide use in Great Britain. Computers and Electronics in Agriculture 42, 43-49.
Willoughby, I., Evans, H., Gibbs, J., Pepper, H., Gregory, S., Dewar, J., Pratt, J., McKay, H. (2004). Reducing pesticide use in forestry. Forestry Commission Practice Guide 15, Forestry Commission, Edinburgh, 140 pages.
Or for a free copy of the papers, please contact the author.
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