Herbicide Use

Only federally-approved and FSC-sanctioned herbicides are used on the Sudbury Forest. Herbicides are applied only by provincially licensed applicators.


Why Use Herbicides?

Before effective forest fire control was in place, fire was the driving force in regenerating the forest.  Hotter fires (dry conditions and high amount of fuel) burned the organic forest floor 'litter' to create receptive seedbeds for newly-released seeds.  Less intense fires may have killed trees like poplar but would stimulate the root system to send up thousands of new stems.  The resulting natural forest landscape was a patchwork of relatively pure species stands.  Before effective fire control, a given patch of forest would burn and regenerate every 60 to 100 years.

Harvesting does not cleanse the forest like fire can.  However, stands of hardwood species like poplar, birch, and maple regenerate naturally and aggressively to those same species following harvesting.   Even with no active management following harvest, we can be assured that those species will continue to thrive on the landscape.

Stands of conifers like pine and spruce seldom regenerate back to those same pure-species conditions without intervention.  Root and stump sprouts from even a small number of hardwoods can dominate a newly-establishing stand that had been mostly pine and spruce at time of logging.  The forest floor is full of seeds of woody and non-woody species that are stimulated to germinate once heat and light reaches it after logging.  These species get established and grow much faster than pine and spruce.  Intervention is required to give pine and spruce a chance to get established - similar to weeding a garden. 

Without effective tending, purer stand of conifers get converted to hardwood stands, or mixedwood stands at best.  The forest landscape changes to the detriment of the forest industry as well as forest dwelling wildlife that depends on that forest condition.

Unfortunately no practical alternative to herbicides exists.  Brushsaw work is not effective, particularly early in the establishment phase when non-woody plants are competing with small pines and spruce.

A report from Nova Scotia showed that when herbicides were not used following the planting of conifer crop, plantation success rate was 3 percent.  Ten percent of the plantations had potential for success with further intervention, but 87 percent of the plantations failed.

Herbicides Used in Forest Management in the Sudbury and North Bay Area

Only federally-approved and Forest Stewardship Council-sanctioned herbicides are used on the Sudbury and Nipissing Forests. Herbicides are applied only by provincially licensed applicators.

Most of the herbicide applied on the Nipissing and Sudbury Forest has the active ingredient ‘glyphosate’.  Trade names of products used include Vision (LabelMaterial Safety Data Sheet), VisionMax (LabelMaterial Safety Data Sheet), Vantage Forestry (LabelMaterial Safety Data Sheet) and Forza (Label, Material Safety Data Sheet).

A lesser amount of Garlon XRT (Label, Material Safety Data Sheet) with active ingredient ‘triclopyr’ is also used.

Notes on the Herbicide Vision from Manufacturer Monsanto

The active ingredient in Vision is glyphosate.  Vision has an identical formulation to WeatherMax, a common agriculture and industrial herbicide.

How Does Vision Herbicide Work?

Glyphosate inhibits an enzyme that is essential to formation of specific essential amino acids in a plant.  It is absorbed through leaves and translocated throughout a plant’s vascular system.

Acute Toxicity

The United States Environmental Protection Agency (EPA) ranks acute affects of exposure to a substance into one of four categories, with ‘I’ being the most toxic and ‘IV’ being the least toxic.  Glyphosate is rated as an EPA Category IV compound in oral rat tests.

Substance LD50 (mg/kg) Toxicity Rating
Alcohol >7500 Very Low
VisionMax >5000 Very Low
Vision >5000 Very Low
Vantage >5000 Very Low
Forza >4000 Low
Table Salt 3000 Low
Garlon XRT 2966 Low
Vitamin A 2000 Low
Aspirin 1000 Moderate
Caffeine 200 Moderate
Nicotine 53 Moderate
Arsenic 15 High
Warafin 1.6 High

For a longer list of compartive Acute Toxicity with other substances, please click here - Acute Toxicity of Several Substances

Chronic Toxicity

Extensive toxicological studies have determined that glyphosate does not cause tumours in laboratory animals.  The US Environmental Protection Agency classified glyphosate as Category E (evidence of non-carcinogenicity for humans), the most favourable rating in the scale.

Studies have shown that glyphosate does not cause birth defects or reproductive problems in laboratory animals.  Pregnant rabbits and rats given high-dose levels of glyphosate delivered normal offspring.  An extensive battery of mutagenicity and genotoxicity assays designed to evaluate gene mutations, chromosome aberrations, and DNA damage and repair showed that glyphosate does not interfere with the genetic make-up of cells.

Skin Exposure

Human clinical studies comparing Roundup Original, baby shampoo, dishwashing detergent, and a household cleaner found that the effects of Roundup and shampoo were indistinguishable from each other and were less irritating that the other two products.

Environmental Fate

Vision does not persist in the environment - it is degraded by microorganisms naturally present in the soil.  The average half-life of glyphosate in soil is less than 45 days.  Studies have shown that glyphosate does not accumulate in the environment after repeated applications over several years or after repeated applications in one year.

Wildlife Effects

Glyphosate is poorly absorbed when ingested.  Any absorbed glyphosate is rapidly eliminated, resulting in minimal tissue retention.  Feeding studies with chickens, cows, and pigs have shown extremely low to no residues in meat and fat following repetitive exposure.  Quebec Ministry of Forests researchers studying glyphosate residues in moose and deer shot during the hunting season concluded that the risk of glyphosate exposure from the consumption of this meat is very low.

Moose browse and browse-use reductions following conifer release may last up to four years.  Early reductions in browse availability commonly found in treated areas may be offset by later additions.  Such increases have been recorded eight growing seasons after treatment.

Responses of small mammals to glyphosate treatment are species specific.  Only short term (one or two years) reductions in some small mammal densities have been reported.  Some small mammals are unaffected while some select and others avoid herbicide treated areas.

Effects on Birds

The Canadian Wildlife Service concluded that changes to habitat as a result of 7 to 9 years of glyphosate use in the Lower St. Lawrence Region yielded an increase in the density of several breeding bird species and an increase in avian diversity.

Hatchability and time to hatch chicken eggs were found to be unaffected by application of Roundup Original herbicide at three different concentrations and four different embryo ages.

Effects on Water, Fish and Other Aquatic Life

The half-life of glyphosate in non-sterile water with sediment is less than 8 days.

Vision herbicide applied at common-use rates does not cause death, growth rate or migrational changes in fish or direct measurable effect on aquatic or terrestrial invertebrates even when intentionally sprayed over water.

More information about glyphosate-based herbicides

Frequently Asked Questions On the Use of Herbicides in Canadian Forestry

Vision – Effects on Mammals and Berries
Roundup Ecotoxicological Risk – Contact VFM for print copy of full article
Roundup Human Risk and Safety – Contact VFM for print copy of full article

Please view a presentation by Canadian Forest Service, Natural Resources Canada researcher Dean Thompson ‘Environmental Fate & Potential Effects of Glyphosate (Vision) Herbicide in Canadian Forest Ecosystems

Concerns about glyphosate

Read a paper that expresses concerns about the safety of glyphosate (NCAP) and reviews of that paper (Dost, Felsot) that respond to those concerns.

Response to International Agency for Research on Cancer (IARC) - March 2015 Release re: Glyphosate “probably carcinogenic to humans”

On March 20th, 2015, an article appeared in the online journal the Lancet Oncology entitled “Carcinogenicity of tetrachlorvinphos, parathion, malathion, diazinon, and glyphosate”, the article was produced by the International Agency for Research on Cancer (IARC) which is connected to the World Health Organization (WHO)

A link to the article is provided here.

In the article, the agency reclassified glyphosate as Category “2A” designation—“probably carcinogenic to humans”. 

There have been a number of rebuttal articles to the IARC report that were released by various industry groups and research orientated individuals:







Key Points:

Only a small sample set of papers were used in making the IARC determination of the classification which took only one week.  Around the world, glyphosate has been undergoing a 4 year comprehensive re-registration review by many world bodies including Health Canada’s Pest Management Regulatory Agency (PMRA) -  none of whom have made this link. Here is what PMRA had to say about the IARC review:

“The World Health Organization's (WHO) International Agency for Research on Cancer (IARC) recently assigned a hazard classification for glyphosate as "probably carcinogenic to humans". It is important to note that a hazard classification is not a health risk assessment. The level of human exposure, which determines the actual risk, was not taken into account by WHO (IARC). Pesticides are registered for use in Canada only if the level of exposure to Canadians does not cause any harmful effects, including cancer.”

Full PMRA link


IARC Group 1: Carcinogenic to humans – Selected familiar items
Alcoholic beverages
Coal, indoor emissions from household combustion
Engine exhaust, diesel
Leather dust
Nickel compounds
Outdoor air pollution and the particulate matter in it
Painter (workplace exposure as a)
Salted fish (Chinese-style)
Silica dust, crystalline, in the form of quartz or cristobalit
Solar radiation
Soot (as found in workplace exposure of chimney sweeps)
Tobacco, smokeless
Tobacco smoke, secondhand
Tobacco smoking
Ultraviolet-emitting tanning devices
Wood dust
IARC Group 2A: Probably carcinogenic to humans - Selected familiar items
Frying, emissions from high temperature
Hairdresser or barber (workplace exposure as)
Lead compounds, inorganic
Petroleum refining (workplace exposures in)
Shiftwork that involves circadian disruption


Notes on the Herbicide ‘Garlon XRT’ from manufacturer Dow AgroSciences

How Garlon XRT Works

Triclopyr, the ester formulation herbicide in Garlon XRT, mimics the natural plant growth hormone auxin.  Auxin controls cell elongation and thus plant growth.  Triclopyr imitates auxin but causes mature cells to elongate – this breaks cell walls and stops movement of water and nutrients in the plant.  Lack of water and nutrients at growing points causes the plant to die.

Triclopyr (and Garlon XRT) have been thoroughly tested through environmental, residue and toxicological trials.  Both the Environmental Protection Agency and Agriculture Canada have run risk assessment of this herbicide and established that it is safe when used as labelled.

Acute Toxicity

Acute toxicity is usually shown as an LD50 – the dose in milligrams of substance per kilogram of test animal body weight, at which half a population of test animals dies.  The tests for this are standardized and carefully run so the LD50 number is a good way of comparing the acute toxicity of substances.  The following table shows the LD50 of triclopyr, Garlon XRT and several other common substances.  For hazard classification purposes, Health Canada rates Garlon XRT as moderately toxic:  High <100 mg/kg, Moderate 100 to 1999 mg/kg, Low 2000 to 5000 mg/kg, Practically None >5000 mg/kg.

Substance LD50 (mg/kg) Toxicity Rating
Alcohol >7500 Very Low
VisionMax >5000 Very Low
Vision >5000 Very Low
Vantage >5000 Very Low
Forza >4000 Low
Table Salt 3000 Low
Garlon XRT 2966 Low
Vitamin A 2000 Low
Aspirin 1000 Moderate
Caffeine 200 Moderate
Nicotine 53 Moderate
Arsenic 15 High
Warafin 1.6 High


Chronic Toxicity

Extensive long-term testing (monitored by Health Canada) has produced no evidence that triclopyr or Garlon XRT causes tumours, birth defects, or changes in parent animals’ genetic material.  Mammals do not break down triclopyr or accumulate it in their body fat.  If exposed to triclopyr they excrete it rapidly and unchanged in the urine.  This means that bioaccumulation does not occur.  Animal and human exposure studies have shown triclopyr consumed in the diet will be cleared from the body in three days.

Skin Exposure

Triclopyr is non-irritating to the skin on a single exposure.  Even a prolonged single exposure to concentrated Release is unlikely to be absorbed through the skin in harmful amounts.  Repeated exposures to Garlon XRT may cause sensitivity similar to an allergy in some individuals, resulting in skin irritation.

Environmental Profile:  Mammals

Mammals do not metabolize triclopyr.  If ingested, triclopyr is rapidly excreted unchanged.  Animal studies have shown that triclopyr consumed in the diet will be cleared from the body within 3 days of intake, with no accumulation in body organs or fat.

Triclopyr has moderate acute oral toxicity.

Extensive, long-term testing has produced no evidence that triclopyr causes carcinogenic, mutagenic or teratogenic effects in mammals, including humans.

Animal dietary tests to determine the effects of frequent, long term ingestion of triclopyr on mammals, established the no-observable-adverse-effect-limit as 2.5 to 5.0 mg/kg/day.  Animals will not receive this level of exposure – directly or through eating treated foliage – due to the operational use of Garlon XRT.

Environmental Profile:  Birds

Triclopyr has a very low toxicity to birds.  Consequently, environmental exposure should not result in any significant acute hazards to birds.  In a one-generation reproduction study, mallard duck and bobwhite quail showed no effects when exposed to triclopyr in their diet.

Environmental Profile:  Soil

Triclopyr has an average half-life of 46 days, with the range being 30-64 days, varying with soil moisture content and temperature.

Soil moisture converts Garlon XRT to triclopyr acid.  Triclopyr acid is degraded rapidly by soil microorganisms (fungi and bacteria).  Final breakdown products are carbon dioxide, water and organic acids.  Triclopyr has little herbicide activity in soil, therefore residual soil activity is of no biological significance.

Triclopyr is considered to have only slight potential for mobility in forest soils because it adsorbs to organic matter in the upper 15 cm of the soil.  This ensures the molecule stays in contact with the microorganisms that are degrading it.  There is little risk of triclopyr reaching ground water, and it poses no significant environmental hazard due to leaching.  There is little lateral movement of triclopyr in soil.

Environmental Profile: Water, Fish and other Aquatic Life

Half life of triclopyr to triclopyr acid is 1 to 6 hours, half life of triclopyr acid in solution is 3 days.  In water sunlight (UV light) and water breakdown triclopyr molecules.

Triclopyr ester has a higher order of toxicity to fish – due to de-esterification at the gill membranes.  Used following label directions, Release poses no threat to fish.

Triclopyr acid has a very low toxicity to other aquatic organisms.

Environmental Profile:  Air

Garlon XRT can be volatile in warm weather requiring management when applying under warm conditions.

More Information about Triclopyr

Fact Sheet - Orgeon State University

Risk to Workers - BC Ministry of Forests