Report to: General Committee Date Report Authored: March 22, 2010
SUBJECT: Giant Hogweed Control Strategy
PREPARED BY: Mark Ingwersen, District Manager – Operations West,
Ext. 3000
Nory Takata, Parks Planner, Ext. 3226
RECOMMENDATION:
1) That the report entitled Giant Hogweed Control Strategy be received;
2)
And that Council approve Option
3 – ‘Treatment with Glyphosate’ as the preferred strategy option to address
eradication and control measures for Giant Hogweed in
3) And that Council acknowledges that this Control Strategy represents the first year of a multi-year program;
4) And that Council approve funding in the amount of $30,000 be allocated from Parks Operating Account # 730-730 5399 to implement control measures;
5) And that Staff be authorized and directed to do all things necessary to give effect to this resolution.
PURPOSE:
The purpose of
this report is to demonstrate the importance of initiating effective control
measures to suppress the spread and reduce the number of Giant Hogweed
(Heracleum mantegazzianum) plants found growing in
BACKGROUND:
Giant Hogweed is an invasive alien plant species with serious human health and environmental implications. The clear sap stored in vesicles along the stem, stem hairs and hairs on the underside of the leaves, contains compounds (furanocoumarins) that sensitizes skin exposed to direct sunlight. Upon exposure, a photo-toxic reaction results in a skin condition known as photo-dermatitis. Characteristic symptoms of this condition include severe burns and blisters at onset, followed by discolouration and scarring of the skin over the longer term. When eye tissue is exposed to the sap, temporary or even permanent blindness can result.
Giant Hogweed can increase erosion along stream banks (by displacing native riparian vegetation) and can measurably decrease the biodiversity of natural ecosystems, in the absence of controls.
Giant Hogweed remains vegetative for two to four years after germination, after which it flowers and produces seed. It is generally considered to be monocarpic, which means that the plant dies after flowering and setting seed. Seeds remain viable for seven or more years, but the seed bed can be effectively exhausted in three to five years if control measures used effectively destroy the entire plant, including the root.
Acting on a resident’s call to the Contact
Centre, Operations staff initially identified Giant Hogweed plants at
On June 4, Operations staff began installing warning signs at strategic locations within the known infestation area, to mitigate the risk to public safety. During this same week, the three public schools bordering on the infestation area were notified of the safety risk posed by Giant Hogweed via Thornhill School Trustee Susan Geller. To augment public awareness and safety, additional signs containing photo images of Giant Hogweed plants were installed to help the public to correctly identify these hazardous plants.
Along with the installation of warning signage, a Landscape Service contractor was hired to perform the manual removal of Giant Hogweed plants growing along pathways, fence lines and in close proximity to active park areas where the maximum risk to public safety resides.
To broaden and increase the level of public
awareness of this danger, mixed media copy was published on the Town page in local
newspapers. More detailed
Collectively, the actions summarized above
lead towards the objective of risk management or abatement, but not towards
effective control or eradication of this invasive species. A thorough review of
the available
Although Operations staff did attempt to map the size and distribution of the Giant Hogweed infestation, heavy undergrowth, difficult terrain and time constraints made a complete survey impossible to achieve. Since these plants are amongst the earliest to emerge in the spring, a more complete survey using hand held GPS devices could help establish an accurate map of the infestation at the same time control measures are being deployed. Monitoring the plant population at this level of detail is essential to manage and monitor the control program, by establishing the location of seed beds where plants have been removed or destroyed, along with facilitating site revisits to evaluate the effectiveness of control measures and adapt the program accordingly.
A short list of
‘best practice’ control methods have been selected on the basis of a
comprehensive review of current scientific literature and the empirical
evidence provided by representatives of the Greater Golden Horseshoe Invasive
Species Working Group. This group includes staff from the municipal and
regional jurisdictions of
|
Option |
Advantages |
Disadvantages |
Cost |
|
|
|
|
|
|
Status quo: signage as required
to notify public |
- cost avoidance and
no chemical use |
- enable the current
infestation to spread and increase in vigour - increased risk to
public health and environmental degradation |
- minor cost for
signs, no additional budget or resources required |
|
|
|
|
|
|
Manual removal of plants (including
10 – 14 cm. of taproots) |
- low environmental impacts; will prevent the re-growth of a limited
number of plants; no chemical use |
- labour intensive
and costly - increased risk to
removal crews - removal and
disposal costs - not practicable on
slopes or near stream banks - may contribute to
soil erosion - plant population
likely exceeds capacity for removals in one season, resulting in the spread
and increased vigour of untouched Giant Hogweed stands |
- although the full
extent of the infestation has not been determined, staff estimate funding of
up to $100,000 on an annual basis for the foreseeable future to achieve a
measure of control |
|
|
|
|
|
|
Treatment with Glyphosate |
- potential to
eradicate high percentage of existing Giant Hogweed population - more effective
than manual removal - cost avoidance
compared to manual removal - potential to
reduce the status of the current population of Giant Hogweed from an
infestation to the occasional isolated stand, over time - environmental impacts can be minimized by using a stem injection
system to ensure all chemical remains within plant tissue |
- public concerns
about use of chemicals - environmental
impact – potential risk when using pesticides |
- although the full
extent of the infestation has not been determined, staff estimate annual
program funding of approximately $30,000 for up to a five year period to
reach control targets |
Staff recommends Option 3 as the preferred Control Option. The use of herbicide in this instance is preferable and commensurate to the consequences of allowing this dangerous, highly invasive plant to increase in number and to spread beyond the current infestation area. Integrated Pest Control principles dictate that control methods be selected to achieve maximum effective control and to minimize negative environmental, economic and social impacts.
Giant Hogweed poses a greater threat to
human health than Poison Ivy, for which Council has previously consented to the
use of Glyphosate to control. Option 3 conforms with fundamental IPM principles
and is consistent with the Town’s former Municipal Cosmetic Pesticide Use
By-law and Policy, as well as the
Quite clearly, Options 1 and 2 will not
succeed in eliminating the threat to public safety or in preventing the
degradation of the ecology of sensitive natural areas. It should also be noted that the following
municipalities and regional jurisdictions are currently employing Glyphosate to
control Giant Hogweed:
FINANCIAL CONSIDERATIONS AND TEMPLATE: (external link)
Staff recommends the allocation of $30,000 be diverted from the hand removal of weeds on hard surface medians (acct. # 730-730 5399) to be used for the full support of option 3 or in partial support of option 2, in 2010. In 2009, weeds were removed on medians 3 times. Under the Council approved Enhanced Cultural Practices Program, additional funding of $30,000 was provided to allow weed removal a fourth time in 2010.
HUMAN RESOURCES CONSIDERATIONS
None
ALIGNMENT WITH STRATEGIC PRIORITIES:
This report aligns with and contains recommendations aimed at protecting the Environment through the control of this invasive plant species and Public Safety from the same.
BUSINESS UNITS CONSULTED AND AFFECTED:
Not applicable
RECOMMENDED
BY: ________________________ ________________________
Paul Ingham Peter Loukes
General Manager, Operations Director, Operations
Brenda Librecz
Commissioner, Community and Fire Services
ATTACHMENTS:
Appendix 1 – Giant Hogweed Infestation Sites
Q:\Commission
Share\Operations and Asset Management\Reports\2010\Operations\Parks\Giant
Hogweed Control Strategy.doc