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Commercial Arborist License

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 examination is given by appointment only. Once DEEP has received your application and fee, you will be scheduled for the next available date.  If you want to take the exam on a specific date, please indicate that on the top of your application and DEEP will try to accommodate that request. If the exam proctor does not have an application for you, you will be denied taking the exam.  There is a $200.00 fee to take the exam.  The examination is given in two parts. The first part consists of a written test and the second part consists of a tree identification test and an oral test.  You should take the written exam a month before the tree identification/oral exam is given.  

The written test is multiple choice with questions regarding pesticide safety, the field of arboriculture and the diagnosis and control of specific diseases, insects and disorders of trees. If an applicant fails the written exam, a re-examination appointment requires another application and $200.00 examination fee. A "No Show" will be considered a failure and the $200.00 examination fee is forfeited.

After passing the written test, applicants will be notified and scheduled for the second part of the examination, which normally takes place at the Connecticut Agricultural Experiment Station in New Haven on a separate date.  The oral exam date is December 11, 2019.   The oral exam dates for 2020 are March 11, June 10, September 9, and December 9, 2020.  There is no additional charge for the second part of the exam.

Applicants who fail the tree identification test will not proceed to the oral test.   Applicants who pass the tree identification test will continue on to the oral test later on the same day. Applicants who fail either the tree identification or oral test will be required to retake the entire examination starting with the written test. This will require a new application and $200.00 examination fee. The first part of the examination (the written test) is given monthly and the second part (the tree identification and oral tests) is given on a quarterly basis.  Examinees have 80 days to complete the exam process both written and tree identification/oral exam.  A "No Show" will be considered a failure.

To be scheduled for the written test, complete the Application for Commercial Supervisory and/or Arborist Examination (Word Form; PDF) and submit it along with the required fee (check or money order for $200.00 payable to the Department of Energy and Environmental Protection) to the address indicated on the application form. Be sure to sign and date the form.

Payment Information:

Any fee submitted with a hard copy application, by mail, shall be paid by check or money order to the Department of Energy and Environmental Protection. Do not send cash in the mail. 

Cash Payments:

To pay in cash, the required fee along with completed applications/documents must be delivered to the Central Permit Processing Unit (CPPU) at DEEP (79 Elm Street in Hartford, CT). The exact fee amount must be provided; the department cannot provide change.

Credit Card Payments:

To pay by credit card, the card holder and only the card holder must come to the Central Permit Processing Unit (CPPU) at DEEP (79 Elm Street in Hartford, CT). They must bring all completed applications/documents that are being processed in the transaction.

A receipt will be provided for the fee payment and the applications/documents will move forward to be processed.

License Requirements
The applicant for a license is expected to possess a working knowledge of basic tree biology, the kinds of operations performed by an arborist and the reasons for performing them.  Outlined below are areas in which an applicant should be proficient.

Additionally, please review the Arborist Examination Reference Materials. These materials may be useful in preparing for the arborist license exam.

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.

  1. Generally, any pesticide application indoors belongs with the structural certifications. Controlling pests on plants indoors will be permitted with the interior plantscape certification.
  2. Outdoor pesticide applications with a structural certification would be permitted in situations such as:
    1. for termite or rodent control if the applicator holds a termite or rodent certification;
    2. for control of structural pests that enter from outside, such as clover mites or earwigs, on the outside foundation of the house and on grass in the immediate vicinity of the foundation; and 
    3. for wasps if the nest is in the immediate vicinity of the house.
  3. Outdoor pesticide applications with a structural certification would not be permitted for insects that are only casually a pest indoors. For example: 
    1. if a heavy flight of aphids is bothersome to people on a porch, a structural certificate holder would not be allowed to spray the plants in the yard from which the aphids came; or
    2. if wood roaches are coming to lights on a porch, a structural certificate holder would not be allowed to treat outside areas.
  4. The ornamental and turf certificate holder could also:
    1. spray for clover mites or earwigs on the outside foundation of the house, but not within the house;
    2. spray for ticks outdoors; and 
    3. control Canada geese on a lawn using general use repellents.
  5. The division between the arborist license and the ornamental and turf certification is as follows:
    1. A tree is defined as a single stem plant which at maturity reaches more than 5 meters high. The application of a pesticide to anything matching this description can be treated by the arborist.
    2. Generally, any plants that can be reached from the ground with hand operated equipment (not a backpack mist blower) can be treated by the ornamental and turf applicator.
    3. The Connecticut Pesticide Control Act states that the arborist is to treat fruit trees. If a dwarf fruit tree (e.g. crabapple) is used primarily as a small ornamental then either may treat. If the dwarf trees are used for edible fruit production or are in an orchard, they are to be treated by the arborist.
    4. If an uncertified nurseryman plants a shrub or trees on a customer’s property, he may treat that plant to protect his guarantee, if the guarantee is included in the original price of the plant, he may not charge an additional fee for this service.


    • If there are dogwood borers in some shrubby dogwoods, who would be permitted to treat?   The borer could be treated by either the arborist or ornamental and turf applicator in the course of his other work about the yard.
    • If hemlocks are pruned into a hedge, who would be permitted to treat? This would be within the province of the ornamental and turf certification.

Identification, Diagnosis and Tree Biology

The applicant should:

  1. be able to identify all common trees found in the region in their summer and winter condition, including but not limited to, those listed below;
  2. know the normal healthy form of the tree, and its appearance and rate of growth under normal and abnormal conditions;
  3. know the suitability of trees to different sites;
  4. know the factors involved in maintaining tree health and appearance and how to anticipate and control or prevent damage from various causes;
  5. understand the functions of the various parts of the tree, such as leaves, bark, wood, roots, etc. and be able to determine if these functions are being properly performed;
  6. recognize the symptoms and causal agents responsible for injuries, abnormalities and weaknesses, including, but not limited to, those listed below; and 
  7. know the relative susceptibility of different tree species to injurious agents. 
Common Trees Found in the Region Variety of Common Trees Found in the Region

Ash (Fraxinus)

Birch (Betula) Black / Sweet
Paper / White
Cherry (Prunus) Flowering
Dogwood (Cornus) Flowering
Elm (Ulmus) American
Ginkgo (Ginko)
Gum (Nyssa) Black / Sour
Sweetgum (Liquidambar)
Hawthorn (Crataegus)
Hickory (Carya)
Holly (Ilex) American
Horsechestnut (Aesculus)
Linden (Tilia)
Locust (Robinia) Black
Honeylocust (Gleditsia)
Magnolia (Magnolia)
Maple (Acer) Japanese
Mountainash (Sorbus)
Oak (Quercus) Black
Walnut (Juglans) Black
White / Butternut
Zelkova (Zelkova)
Arborvitae (Thuja)
Juniper (Juniperus)
Douglasfir (Pseudotsuga)
Fir (Abies) Balsam
Hemlock (Tsuga) Eastern / Canadian
Larch (Larix)
Pine (Pinus) Austrian
Japanese Black
Eastern White
Spruce (Picea) Colorado Blue
Type of Insects Variety of Insects 
Aphids and Adelgids

Cooley spruce gall adelgid
Eastern spruce gall adelgid
Hemlock Woolly adelgid
Pine bark aphid
Woolly beech aphid  

Bark Beetle and Borers

Black vine weevil
Bronze birch borerDogwood borer
Elm bark beetle  
European pine shoot moth
Pine root collar weevil
Two-lined chestnut borer
White pine weevil

Caterpillars and Loopers

Eastern tent caterpillar
Fall webworm
Forest Tent Caterpillar
Gypsy moth
Oak leaf tier
Oak leaf roller

Leaf Miners

Arborvitae leaf miner
Birch leaf miner
Holly leaf miner


Spruce spider mite
Two-spotted spider mite  


Euorpean sawflyMountainash sawfly
Pine false webworm
Pine sawflies
Redheaded sawfly  


Beech bark scale
Euonymous scale
European elm scale
Elongate hemlock scale
Magnolia scale
Oystershell scale
Pine needle scale
Tulip tree scale
White prunicola scale


Birch skeletonizer
Elm leaf beetle
Oak leaf skeletonizer  

Branch and Stem Canker Diseases

Beech Bark Disease
Black Knot
Bleeding Canker
Botryosphaeria Canker
Chestnut Blight
Cytospora Canker
Hypoxylon Canker
Nectria Canker 
White Pine Blister Rust

Foliage Diseases

Apple Scab
Cedar-Apple Rust
Dogwood Anthracnose
Hawthorn Leaf Blight  
Hawthorn Rust
Horsechestnut Leaf Blotch
Lophodermium Needlecast of Pine  
Maple Leaf Spot
Tar Spot
Oak Leaf Blister
Powdery Mildew
Rhizosphaera Needlecast of Spruce (formerly Spruce Needle Blight)
Spruce Needle Rusts 

Blight and Dieback Diseases

Fire Blight
Sphaeropsis Tip Blight (formerly Diplodia Tip Blight of pine)  

Vascular Diseases

Ash Yellows
Dutch Elm Disease
Elm Yellows (formerly Elm Phloem Necrosis)  
Verticillium Wilt  

Root Diseases

Armillaria Root Rot (formerly Shoestring Root Rot)
Phytophthora Root Rot

Physiological Disorders, Nonparasitic and Miscellaneous Biotic Injuries
Animal, Bird injuries
Air pollutants  
De-icing salts  
Frost injury  
Girdling roots  
Herbicide damage  
Ice, snow, wind injury  
Lightning injury  
Misapplication of chemicals Moisture extremes  
Natural gas, soil pollutants  
Nutrient deficiencies & toxicities   
Soil compaction, grade changes 
Temperature extremes  
New Exotic Pests Recently Introduced in the United States of America  
Asian Longhhorned Beetle
Emerald Ash Borer
Sudden Oak Death
Note:  Although not found in Connecticut yet, the applicant should  have a general awareness of these serious pests  


The applicant should be able to determine and perform the correct and proper treatment to improve the conditions of any tree.  The applicant should know the currently accepted standard practices of arboriculture. This requires knowledge of: 

  1. Tree surgery. The applicant should know the currently accepted standard practices for pruning, bracing, cabling, treating cavities, treatment of girdling roots and other disorders. The applicant should know the tools used for treatment, as well as the strength of such materials as synthetic fiber ropes, steel cable, eyebolts and lag hooks.

  2. Tree nutrition.   The applicant should know the essential chemical elements for tree growth and survival, whether they are obtained from the air or soil, how the tree takes them up, those that are likely to be deficient and the factors affecting deficiencies.  Knowledge of tree fertilization is also required, including how to determine deficiencies of essential elements and how, when, and in what amounts to apply treatments if needed. The applicant should know the significance of soil pH; how it affects nutrient availability and tree growth and how to modify pH in the soil if necessary. The applicant should have a basic understanding of the association of mycorrhizae fungi with tree roots.

  3. Control of insects, diseases and disorders.   The applicant should know precisely when and how to control and treat the insects, diseases and disorders listed in the above tables.  When pesticides are to be applied, an applicant should know the proper use and type of material to use consistent with state and federal pesticide laws. An applicant must know the basic safety and handling rules for pesticide use contained in the Pesticide Applicator Training Manual, as well as restrictions on pesticide use imposed by the Department of Energy and Environmental Protection (DEEP).  The applicant should know the basic principles of Integrated Pest Management (IPM) and how to apply these principles to plant health care in arboriculture. 

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 require 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 October 24, 2019

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