Commercial Arborist License

3/11/2021, E-License, a new online licensing service is now live and accepting applications for Pesticide Supervisors in the Arborist category. If you already have a Connecticut pesticide certification please contact us by email for your login information. If you do not already have an account follow the instructions below, please read carefully. Arborist License
An arborist license is required for persons advertising, soliciting or contracting to do arboriculture in Connecticut. As defined in the arborist law, “arboriculture means any work done for hire to improve the condition of fruit, shade, or ornamental trees by feeding or fertilizing, or by pruning, trimming, bracing, treating cavities or other methods of improving tree conditions, or protecting trees from damage from insects or diseases or curing these conditions by spraying or any other method.” The licensed arborist is a supervisory pesticide applicator, with respect to the use of pesticides.  For all intents and purposes “certificate” means “license.”

The arborist license is category 3D under the commercial pesticide supervisor certification. More information about all of the commercial pesticide supervisory categories can be found under the "Commercial Supervisor" page on the left.


Written Exams

  • Multiple choice
  • Need to be taken and passed a minimum of 3 weeks prior to desired oral exam date. Preferably more than a month before.
  • Failure will require a $200 retest fee

Oral Exams

  • After passing the written exam
  • Exam takes place at The Connecticut Agricultural Experiment Station in New Haven on a separate date.
  • First part is tree identification, you must pass that (80%) to continue onto the practical oral exam on the same day. The practical exam consists of 10 questions each from a different category. The categories are listed below. 
  • If an applicant fails the oral exam they will be given one additional attempt before having to retake the written exam.
  • The passing score for the tree ID portion is an 80%, and then you will take the practical exam. You will need a total score of at least 70% on the practical exam, and a score of at least a score of 7 (out of 10) on at least seven of the ten categories. Both the tree ID and practical exam need to be passed in order to be granted an arborist license.

Practical Exam Categories

The practical exam consists of 10 conversational questions one from each of the 10 different categories listed below:

  • Licensing/records
  • Safety
  • General tree work
  • Cabling and bracing
  • Tree physiology
  • Insects
  • Diseases
  • Abiotic disorders
  • Nutrient management
  • Pesticides

Upcoming Oral Dates:

  • June 5, 2024
  • September 11, 2024
  • December 11, 2024

Oral Exam Locations:

June and September: Lockwood Farm, 890 Evergreen Ave, Hamden, CT 06518

  • Gather in the pavilion, ID portion will start at 8:30am

March and December: CAES, 123 Huntington Street, New Haven, CT 06511

  • Gather in the Jones Auditorium, ID portion will start at 8:30am

Reference Materials (***Study information found here***)
The applicant for a license is expected to possess a working knowledge of basic tree biology, the kinds of operations performed by an arborist, pesticide safety, the field of arboriculture and the diagnosis and control of specific diseases, insects and disorders of trees and the reasons for performing them.  Outlined below are areas in which an applicant should be proficient.

General Supervisory Examination Study/Reference materials. **These materials consist of general, core, safety materials that pertain to any supervisory category.

Arborist Examination Reference Materials. **These materials may be useful in preparing for the arborist license exam.

Identification, Diagnosis, Tree Biology, and Treatment Information (**What is covered on the exam**)

Review the following link to see what topics you need to learn about for the exam: Click here to view Species, Disease, and Treatment List * Required Information*

Outlined below are responses to some questions which have arisen concerning what activities are permitted through the structural (General Pest, etc.) and outdoor (Ornamental and Turf) certifications and the arborist license.

Category Clarification ( what can I do with each category) (PDF)

Operational Practices
The applicant should know:
  1. safety rules to be followed in tree work to protect workers, the public, and the environment;
  2. how to recognize electrical hazards and what safe working distances are from them;
  3. types of insurance that protect tree workers, the public, property and the environment; and 
  4. Connecticut laws and regulations pertaining to arboriculture and commercial pesticide application.
  5. NEW! Effective October 1, 2013, Arborists are required to register their business. The Pesticide Application Business Registration now includes registration for arborist businesses. The Arborist or Pesticide Application Business Registration Form is available in two formats: PDF and Word form. 
Other Uses of Pesticides 

The arborist license authorizes the application of fungicides, insecticides, miticides and tree growth regulators to fruit, shade and ornamental trees only.  Additional certification is required for commercial application of pesticides to control diseases, weeds, insects and related pests, in turf, ornamental shrubs, or any other crop or site.  For example: ornamental and turf certification (category 3a) is required for tick applications; right-of-way certification (category 6) is required for control of brush and weeds along roadsides or right-of-ways; aquatic pest control (category 5) is required for control of vegetation in any water bodies within the state.

Useful Phone Contacts

Poison Control Center:  1-800-222-1222
DEEP 24-hour Emergency Spill Reporting:  (860) 424-3338

Sample Examination Questions

1.  An arborist license is necessary to do which of the following for hire?

  1. plant trees
  2. cut down and remove trees
  3. prune and trim trees
  4. kill trees with herbicides
  5.  all of the above

2.  What are objectives of pruning tall shade trees?

  1. topping
  2. to stimulate height growth
  3. crown cleaning, safety
  4. to increase sap flow
  5. all of the above 

3.  Which of the following would likely cause a tree to become more sickly over a period of years, to produce smaller leaves and an open crown? The trunk is without basal flare but soil moisture is adequate to sustain the tree.

  1. late blight
  2. aeration of soil
  3. over fertilization
  4. girdling roots
  5. lightning

4.  The numbers such as 5-10-10 or 10-6-4 on the analysis label of a fertilizer bag indicate

  1. the stock number of the fertilizer
  2. the pounds of nitrogen, phosphate and potash per bag
  3. the percent by weight of nitrogen, phosphate and potash
  4. the pounds of phosphate, potash and nitrogen per bag
  5. the percent by weight of phosphate, potash and nitrogen

5.  Cedar Apple Rust attacks

  1. Ash
  2. Horse chestnut
  3. Oak
  4. Elm
  5. Apple 

6.  Cedar Apple Rust appearance:

  1. wilting
  2. poor growth on one side of  tree
  3. orange leaf spot
  4. leader wilts and dies
  5. yellow leaves

7.  Cedar Apple Rust treatment:

  1. remove infected part of whole tree
  2. spray with lannate
  3. malathion or aramite spray
  4. warfarin
  5. chlorothalonil spray

8.  Cedar Apple Rust when:

  1. dormant
  2. as leaves unfold and 10 days later
  3. October and April
  4. Second week in May
  5. While tree is still healthy

For further information please contact the Pesticide Management Program at (860) 424-3369 or or write to:

Department of Energy and Environmental Protection
Bureau of Materials Management and Compliance Assurance
Pesticide Management Program
79 Elm Street
Hartford, CT 06106-5127

Content Last Updated on April 17, 2023

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