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.

Publications and guidance on forest vegetation management can be found on our publications pages

Integrated forest vegetation management – 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 bialaphos 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 bialaphos 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, bialaphos 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.
• Bialaphos 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).

References

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

Integrated forest vegetation management – Relative efficacy of herbicides for the control of Deschampsia flexuosa

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

Integrated forest vegetation management – The tolerance of young trees to clopyralid

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

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:

• Fraxinus excelsior (ash)
• Prunus avium (cherry)
• Quercus robur (oak)
• Acer pseudoplatanus (sycamore)
• Populus x canadensis cv ‘Ghoy’ (poplar)
• Pseudotsuga menziesii (Douglas fir)
• Pinus nigra ssp. laricio (Corsican pine)
• Larix kaempferi (Japanese larch)
• Picea abies (Norway spruce)
• Picea sitchensis (Sitka spruce).

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.

Practical implications

• When creating new woodlands on good quality farmland, creeping thistle can be very damaging to young trees. Herbicides are often used as this species cannot generally be controlled by mulches, cutting, or shallow cultivation. However, as creeping thistle grows so tall, directed applications of contact herbicides are not practical.
• Clopyralid (as Dow Shield) can control creeping thistle very effectively, when applied as a sequential dose of 0.5 litres per hectare to extending shoots in May, followed by 1 litre per hectare 3 weeks later.
• Sequential doses as described above are generally safe to apply over actively growing trees.
• Where grasses occur in mixture with thistles, cycloxydim (e.g. as 2.25 l/ha Laser), fluazifop-p-butyl (e.g. as 3 l/ha Fusilade Max) or propaquizafop (e.g.as 1.5 l/ha Falcon) are also safe to apply over trees.
• Practical guidance on use of clopyralid, cycloxydim, fluazifop-p-butyl and propaquizafop has been issued in Forestry Commission Field Books (e.g. Willoughby and Dewar, 1995) and a Technical Paper (Willoughby and Clay, 1999). Practical guidance on tree tolerance will be included in a future revised version of Forestry Commission Field Book 8.

References

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.

For further information

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

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

Integrated forest vegetation management – Web-based expert system for advising on herbicide use

Summary (from the scientific paper Thomson and Willoughby, 2004)

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.

Practical implications

• In conjunction with the Canadian Forest Service, a technology demonstrator of an expert system to advise on herbicide selection has been produced.
• The system currently only addresses the choice of a herbicide, for a given month and weed species. Other elements of an integrated approach to forest vegetation management as described in the recently published Forestry Commission Practice Guide on pesticide reduction (Willoughby et al., 2004), such as for example assessing and predicting weed impact, examination of non chemical alternatives, selection of herbicides based on cost and environmental risk, are also amenable to expert system delivery in the future.

References

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.

For further information

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

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