Forest Practices Branch / Procedures
Manual / SITE PREPARATION
Chemical
Contents
1Background...... 1
1.1Suitability of Herbicides for Site Preparation...... 1
1.2Using Herbicides with Other Site Preparation Methods...... 2
2Planning for Chemical Site Preparation...... 3
3Site Preparation Chemicals...... 4
3.1Pesticide Laws and Regulations...... 4
3.2Herbicides Registered for Site Preparation...... 4
Requirements and Characteristics of Herbicides...... 4
4Application of Herbicides...... 5
5Contracting for Chemical Site Preparation...... 6
Revised: December 1993/ Ministry of Forests
Forest Practices Branch / Procedures
Manual / SITE PREPARATION
Chemical
1 Background
Chemical site preparation, which involves the application of herbicides, controls competing vegetation before planting or natural regeneration and during the early stages of seedling establishment. In general, herbicides are effective in suppressing most undesirable vegetation and are well suited for use on many sites. Herbicides, when properly applied, also have little site impact. Proper application implies application according to label instructions. With their minimal site impact, herbicides can offer certain environmental advantages over other site preparation treatments. However, in some areas, application of herbicides are of particular concern to other resource users and members of the public.
1.1 Suitability of Herbicides for Site Preparation
Chapter 13 of Regenerating British Columbia’s Forests, by J. Otchere-Boateng and L.Herring [1990] suggests that for effective site preparation by chemical methods alone, the site must have the following characteristics:
- Live vegetation species that are susceptible to the available registered herbicides.
- Low density of logging residues and other debris.
- Forest floor litter that is thin enough to permit seeding, where natural regeneration is planned, or screefing if artificial reforestation is needed.
If these criteria are met, then chemical site preparation may be an appropriate option for achieving regeneration objectives. Examples of situations favoring chemical site preparation include:
- Where mechanical site preparation is inappropriate due to steep slope and/or sensitive soil.
- Where non-chemical methods provide poor control of sprouting species, or where stored seed might be stimulated to germinate following burning or mechanical treatments.
- Where soil moisture stress is a problem.
- Where burning can lead to loss of nutrients, unacceptable levels of smoke, or inappropriate risk.
- Where site preparation is to be done in poorly accessible and scattered locations in portions of plantations and natural stands which are understocked.
Several drawbacks to chemical site preparation must also be considered. Not all undesirable vegetation in forest communities can be controlled with the available registered herbicides. Herbicide operations can cause shifts in competing vegetation creating situations where minor herbicide-resistant species can develop into a major competition problem after a treatment. In most cases, herbicide application must wait until shrubs and hardwoods have sprouted to ensure maximum uptake and translocation. This can delay reforestation efforts. In some areas, early seral vegetation provides a nurse crop that protects seedlings from frost. A herbicide application that removes this vegetation may increase the incidence of frost damage on newly planted seedlings.
Herbicides are regulated and not allowed to be applied on all sites. For example, sites close to sensitive areas, such as potable water sources and fish-bearing streams. Finally, there is growing public concern over the use of chemicals in the environment. This continues to impact the use of herbicides for site preparation.
1.2 Using Herbicides with Other Site Preparation Methods
Where the objective of site preparation is not vegetation suppression alone, but includes, for instance, removal of flammable logging residues or mineral seedbed preparation, herbicides may be used in combination with mechanical and burning methods (i.e., ‘brown and burn’). For example, on a harvested area invaded by herbaceous and brush species, the green (live) vegetation does not burn readily, and tends to shade logging residues. Shaded residue dries more slowly and may remain too wet to burn. A pre-burn herbicide application to desiccate, defoliate, or kill vegetation can allow the slash to warm and dry, thus allowing a good burn. However, the logistics of combining an effective herbicide treatment with a timely burn may be difficult.
Where brush species on the site are susceptible to herbicide treatments, but removal of the standing dead vegetation and/or logging debris is also required (e.g., for planter access), chemical treatment may best be combined with burning or with mechanical site preparation.
Note that combining herbicides with other site preparation treatments may result in a different and occasionally less diverse vegetation complex than would have been created had either of the treatments been used in isolation.
Herbicide applicators attached to mechanical site preparation implements (e.g.,Bräcke patch scarifier or powered disc trencher) are available but are not commonly used in British Columbia.
Otchere-Boateng and Herring [in Lavender et al., 1990] review the possible combinations of treatment that include herbicides for site preparation.
2 Planning for Chemical Site Preparation
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Planning for chemical site preparation begins with problem identification or assessment of potential vegetation problems at the pre- and post-harvest stages. This is followed by selection of a treatment method. Selection considerations will include: treatment cost; effect of the method on workers, bystanders, crop trees, and the environment (water, fish and wildlife resources); and the potential for obtaining the necessary permits. Planning must include on site monitoring, post-treatment assessment, and prescription evaluation. The evaluation should assess whether reforestation objectives were met. For detailed explanations on each of these steps, see Otchere-Boateng and Herring [in Lavender, et al., 1990] and Herbicide Field Handbook, FRDA Handbook 006 by Otchere-Boateng [1990].
3 Site Preparation Chemicals
3.1 Pesticide Laws and Regulations
The use of herbicides for site preparation, like all other pesticide use, is controlled by federal and provincial laws and regulations. These laws and regulations may be found in various manuals and publications, however, for up-to-date information, see Handbook for Pesticide Applicators and Dispensers: Forestry Supplement [MOF 1991], and the chapter of this manual entitled “Vegetation Management.”
All pesticides are required to be registered by Agriculture Canada and must carry a manufacturer’s label and be used according to the specific instructions on that label. It is illegal to use pesticides in a manner other than that specified on the label.
A provincial pesticide use permit is required for any pesticide to be applied in the forests of British Columbia. Any person applying a pesticide must have special training in pesticide application and be certified by the B.C. Ministry of Environment, Lands and Parks, (Pesticide Management Branch), or be supervised closely by a certified applicator. Project managers must adhere to the laws and regulations governing pesticide handling, storage, and application. See the chapter of this manual entitled “Vegetation Management” or see the Handbook for Pesticide Applicators and Dispensers: Forestry Supplement, [MOF 1991] for more information.
3.2 Herbicides Registered for Site Preparation
The chapter “Vegetation Management” lists the herbicides and examples of their formulations that are registered for forest site preparation. Only glyphosate (Vision®), 2,4-D amine, 2,4-D ester, triclopyr (Release®), and hexazinone (Velpar, Pronone) have forestry registration. The herbicide used most widely in British Columbia forests is glyphosate.
Requirements and Characteristics of Herbicides
A site preparation herbicide must not show extended residual activity in soil, as this could damage crop trees planted in the future. The waiting periods needed for conifer establishment following site preparation using a herbicide treatment are presented in Table13.4 in Otchere-Boateng and Herring [1990]. Where there is no need for saving residuals or naturals, treatment windows can be wider than for release operations. The characteristics of the herbicides registered for site preparation are listed in the Herbicide Field Handbook, FRDA Handbook 006 by Otchere-Boateng [1990].
4 Application of Herbicides
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For vegetation control through chemical means to be effective, the herbicides must be absorbed into plants (via leaves, stems, twigs, or roots) and subsequently translocated (in the case of systemic herbicides) to the site of action in appropriate form and quantity. Herbicide absorption is influenced by several factors:
- herbicide formulation,
- carrier and orientation,
- chemical composition of plant surfaces, and
- weather conditions (particularly temperature and relative humidity).
Translocation is controlled by two sets of factors:
- the inherent properties of the herbicide; and
- plant phenology and condition (e.g., plant vigor, water or drought stress, and damaged plant parts).
Effective vegetation control requires appropriate selection of the following:
- herbicide formulation,
- carriers,
- application rate and spray volume,
- application season and local weather conditions,
- application method,
- and supervision.
Otchere-Boateng and Herring [in Lavender et al., 1990] briefly discuss each factor. Detailed information is available in the Handbook for Pesticide Applicators and Dispensers: Forestry Supplement [MOF 1991] and FRDA Handbooks 005 and 006.
5 Contracting for Chemical Site Preparation
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Detailed procedures for planning, carrying out and evaluating site preparation contracts are discussed in “Project Management.”
Revised: December 1993 / 1