Gypsy moth crisis in Mississauga
Gypsy moth populations have reached critical levels in many areas of Mississauga. Some trees have more than 800 egg masses, which will yield hundreds of thousands of caterpillars per tree when they hatch this spring.
City staff has estimated that more than 10,000 trees are impacted by the infestation which equates to an approximate cost of
$5 million in pruning/removal costs. This figure only includes trees located on city property and does not take into account trees on private property.
The most heavily affected neighbourhoods in Mississauga will be facing a number of problems as a result of the predicted 2006 population levels. If unchecked, the infestation could result in:
• significant environmental alteration
• serious degradation of trees, loss of amenity and aesthetics
• increased costs associated with the removal of lost trees
• reduced property values and tax assessments
• the spread of infestation to other areas of Mississauga and beyond
• an unpleasant or unsafe environment to live and work due to insect droppings silk and hairs shed by the caterpillars
• respiratory or skin irritations from the hairs, silk and droppings of the caterpillar.
Background
During the past 20 years, Mississauga’s Forestry Unit has worked closely with residents providing information and advice on various Integrated Pest Management (IPM) measures to control the gypsy moth, which has no predictable cycle of population growth and collapse.
The IPM measures, which include picking caterpillars off foliage and soaking them in soapy water, placing sticky bands and burlap wraps on tree trunks and scraping off and destroying egg masses, are not effective against heavy infestations such as the one Mississauga is currently experiencing.
Gypsy moth, in outbreak populations, pose special problems to mature oak trees when compounded with other stress factors. Healthy deciduous trees (maples, oaks, etc.) can survive heavy, even total, defoliation occurring over one or even two consecutive years provided there are no other stress factors at work (e.g. drought, root rot). Such trees produce a second lesser crop of leaves and have reduced overall growth. Conifers, (pines, spruce, firs, larch, etc.) unlike deciduous trees, if heavily or wholly defoliated, are killed. Mature oak trees (red, black, white, bur and swamp white) in Mississauga, have been suffering from what is called ‘oak decline syndrome’ for at least the past six or more years.
Monitoring
Mississauga’s current outbreak began to build up two years ago. In August 2003, field inspections indicated a high of 14 egg masses per tree. By August 2004, a survey indicated a high of 185 egg masses per tree. In the spring/summer of 2005, residents began reporting heavy defoliation two specific areas. In July 2005, staff began detailed gypsy moth egg mass surveys.
Numbers of observed gypsy moth egg masses have increased dramatically in three years. In heavily infested areas the average was 800+ egg masses per tree, however a few trees were observed as having 1,500+ egg masses. Egg masses vary in size and egg numbers. Sizes range from the size of a dime with as few as 100 eggs, to larger than a $2 coin with 1,000+ eggs. Not all eggs are fertile, not all will survive to hatch, nor will all hatched caterpillars survive. The average size of the egg masses has increased in the last three years which is a symptom of an increasing population. Taking predation, parasite and pathogen effects into account, the most heavily infested trees may still have 400,000 to 600,000 or more caterpillars emerging per tree and surviving to adulthood.
As population numbers increased, gypsy moth females altered where they lay their eggs. Previously, egg masses were typically laid within three metres (10 feet) of the ground when deposited on tree trunks. Currently the majority of the egg masses surveyed are laid 10+ metres (33+ feet) off the ground. This characteristic is typical of outbreak populations.
Mississauga’s treatment plan
The city hired independent forestry consultant BioForest Technologies to carefully research and examine Mississauga’s gypsy moth crisis and recommend the best solution to handle the infestation crisis.
On March 1, BioForest Technologies and city staff presented two separate reports to Mississauga City Council regarding treatment recommendations. The report from BioForest confirms that high egg mass densities are a cause for concern and recommended the city conduct an aerial spraying program within outbreak areas in order to prevent the loss of trees. They recommended two to three applications of the bacterial insecticide Bacillus thuringiensis var. kustaki (Btk) in the spring using a twin engine helicopter. In addition to the aerial spray program, BioForest recommended the implementation of an Integrated Pest Management (IPM) program involving residents in order to help mitigate damage on private property.
The city’s staff report endorsed BioForest’s recommended treatment plan and recommended proceeding with the selection and contracting of an aerial pesticide applicator and obtaining necessary approvals the Ministry of Transport.
The intent of the aerial spray is to reduce the gypsy moth population level, not eradicate them. The Btk applications will focus on caterpillars located high in tree canopies and the city is urging all residents, regardless of whether they are in a spray zone or not, to remove and destroy all egg masses within reach.
Through public meetings, a survey and ongoing discussions residents in heavily infested areas are in full support of the city’s recommended aerial spray treatment and are looking to the city to develop coordinated treatment approach for trees on both public and private property. An uncoordinated approach to dealing with the infestation using chemical pesticides may have damaging environmental and human health consequences. That is why the city’s recommended treatment plan is consistent with its environmental policies, meets IPM standards and has been deemed the healthiest and most effective method of dealing with the infestation by Region of Peel’s Medical Officer of Health.
For more information on Mississauga’s gypsy moth infestation or to obtain copies of staff reports and the consultant’s report, visit www.mississauga.ca/pestmanagement
