Herbicides may be used to control undesirable vegetation on areas considered for planting or seeding on some sites. The application of herbicides for vegetation management (e.g. SIP, stand release) is implemented through the Manitoba Forestry Branch.
There are an increasing number of situations where chemical site preparation methods can give dependable results where mechanical site preparation as a single treatment cannot. In Manitoba, chemical site preparation treatments are normally used in conjunction with mechanical treatments, in situations similar to the following:
Ground-spot (or band) applications can reduce immediate competition around planting spots, and may be associated with a mechanical treatment e.g. Bracke herbicider. In situations where vegetation control is required following mechanical site preparation, wait at least one year after site disturbance so that target vegetation can recover and adequate foliage is present. Another possible combination is the use of herbicides on heavy shrub competition and subsequent prescribed burn prior to planting or seeding.
If the site is to be burned or mechanically prepared following a herbicide treatment, allow 6 to 8 weeks prior to site disturbance to ensure adequate vegetation control.
Site preparation using herbicides to control vegetation as a single treatment creates distinct features. Additional considerations associated with this treatment are:
Grassy sites with little slash and difficult access are more appropriate candidates for chemical site preparation when no other site preparation treatment is applicable (i.e. mechanical, prescribed burn). Timing of application is dependent on the mode of action (eg. translocation) for the herbicide used, therefore users must consult chemical labels and literature. Methods of chemical site preparation include broadcast applications, spot and band applications, and by tree injection.
Chemical treatments for stand tending are used to achieve plantation release and possibly thinning.
Herbicides provide a viable alternative for improving both the density and composition of timber stands. Recently developed methods of injecting and implanting herbicide sprays, pellets, or capsules directly into target tree stems can reduce potential for environmental contamination and worker exposure. The cost of chemical treatment, depending on the situation, is often significantly lower than that of mechanical treatments. Chemical treatment produces a situation similar to the natural system because the target trees are left standing, to be assimilated slowly into the downed woody fuels, provide a more continuous supply of large woody material for the nutrient cycle, and protect living trees from sun scald and wind injury. Some site characteristics to consider when evaluating areas for herbicide application (release from competition) are distinguished into three main categories, as follows:
Site Description: land status/ownership (management objectives), site class (ecosystem classification vegetation types), growth & yield, depletion activity, environmental sensitivity.
Crop Attributes: height, vigour, age, stocking, density, distribution, species silvics, herbicide tolerance, and ability to respond to release.
Competition Attributes: species silvics, height, longevity, leaf area index, susceptibility to herbicides, other competitors beneath dominant competitor, effective timing of chemical treatments.
Success of chemical treatments is dependent on:
Predicting vegetation response and effectiveness of the application is based on past experience and applied knowledge of site and species. Follow-up assessments are often necessary to confirm the effectiveness of herbicide treatments.
Aerial application methods are primarily used for plantation release programs that include large treatment areas. Presently, Glyphosate is the only registered chemical for aerial application in Manitoba. Glyphosate is a broad-spectrum herbicide, and applied as directed (from label) to the foliage of actively growing brush and trees at the proper stage of growth will effectively reduce weed and brush competition from desirable tree species. Glyphosate translocates throughout the treated plant. It moves from the foliage into the stems and down into the roots to control the whole plant, preventing re-growth from underground reproductive parts. Applications for conifer release must be made after formation of final conifer resting buds in the fall, and 3 to 4 weeks prior to killing frost and leaf drop of the deciduous species. Glyphosate needs adequate leaf surface area for absorption into the weed. Best results are obtained on woody brush and trees when application is made on actively growing plants in late summer or fall.
Ground application methods include; broadcast from machine with cluster nozzle or Radiarc, backpack sprayers applied manually, injection systems (hack and squirt) implemented manually. Ground applications of herbicides are used on small treatment areas for brushing and weeding or sanitation spacing (i.e. pre-commercial thinning). The hack and squirt method can be applied in a juvenile spacing treatment, but is difficult to control. Results from the hack and squirt method are unknown at treatment, and necessitate future assessment to confirm treatment success. Manual ground application methods are restricted to lower density sites (less than 10,000 stems per hectare) to accommodate easy maneuverability and increase overall productivity.
Global Positioning Systems (GPS) and Geographic Information Systems (GIS) technology has been incorporated into the vegetation management programs with the goal of better tracking of the project application and better record keeping via computer databases and spatial files (maps). This will also have the benefits of allowing better feedback to the equipment operators regarding their techniques. In both ground and aerial broadcast applications, Forestry Branch makes use of Automatic Flow control, data collection and navigational guidance technology. The use of these technologies ensures consistent application rate, precise digital records of the application and accurate placement of herbicide in the treatment blocks. Long-term monitoring of the results will allow for better application prescriptions via forestry staff.
The 'Regional Herbicide Application Proposal' requires forestry staff in each region to determine and identify areas that are in need of chemical treatment (usually plantation release). Areas proposed for treatment should address the management objectives within the region, taking into account potential impacts on other resources within or in the vicinity of treatment blocks (approval from Integrated Resource Management Team). Upon submitting Regional Herbicide Application Proposals to the Forest Health and Renewal Section at Head Office, the silviculture forester and the pesticide application technician will schedule site inspections with the regional forestry staff.
Key points brought up at the site inspections are: site characteristics and history, composition of competition, competition development, crop response to treatment, and treatment success rating. Application rates and methods are also recommended at the site inspection. The rate of application (litres/hectare of herbicide) depends on the composition of control species (hardwood, shrubs or grass) and the method which chemicals are applied. Aerial versus ground applications may require different volume loading (i.e. active chemical ingredient/water ratio).
The Silviculture Forester and Pest Management Forester will prioritize regional proposals following site inspections in all regions for the provincial program. Herbicide application proposals are provincially prioritized according to the following constraints: response to treatment, treatment success rating, funding, and equipment/manpower available.
The Applications Specialist(s) have the following responsibilities:
During application, the Forest Health and Renewal Section may establish monitoring plots to assess levels of competition before and after spray operations. Plots will be re-measured and/or inspected the year following spray operations by staff from silviculture and the region. A 'Forest Health and Renewal Section Herbicide Application Follow-up Report' is completed based on the results gathered from re-measurements and/or inspections. Finally, the 'Annual Provincial Herbicide Application Report' is filled out by the Section to complete the process, and summarize the program.