When an invasive species is detected we must respond rapidly before it becomes established or spreads to other areas. If we are going to slow an invasive species down or stop it all together, our success depends on quick action to control and eradicate it. Control of invasive forest pests can be undertaken through several methods, including chemical control, biological control, or physical (mechanical) control. Control efforts could have different goals, such as complete eradication of the pest, reduction of the density of the pest in an infested area, or reduction of a pest’s spread (NRCan, 2013).

Photo: Taylor Scarr, OMNRF
After detection of Asian longhorned beetle in Mississauga, Ontario, forestry professionals responded quickly to control the outbreak. All potential host trees were removed from the area of infestation and the wood was destroyed by chipping.

Chemical Control

Chemical control involves the application of pesticides, herbicides, fungicides, or insecticides. These chemicals should always be applied using proper equipment and personal protective gear. Further, it may be prohibited to apply chemical controls in certain areas, such as in sites where rare or endangered species are present, so it is essential to determine the proper protocol for all areas and chemicals (Wisconsin DNR, 2012).

Biological Control

Biological control is when a living organism is used to reduce or eliminate the population of an invasive species. The organism used as the biological control may either consume the invasive pest or cause it to become diseased (OMNRF, 2014). In most cases, a biological control is brought from the original habitat of the invasive pest, where it acted as a natural enemy of the species. However, the use of foreign organisms as a biological control must be carefully assessed, researched, tested, and monitored to ensure that the control does not become invasive itself. If a biological control is also a non-native organism, there is a risk that it will also become invasive causing additional damage to that of the invasive species it was brought in to control (OMNRF, 2014). There are several types of biological controls that could be used


Insect parasitoids have an immature life stage that develops within or on another insect host and ultimately kills the host. Parasitoids slowly kill their hosts by paralyzing them, feeding on their tissues, or laying eggs inside them. Insect parasitoids are specialized in their choice of hosts and only the female will search for a host. Parasitoids also vary in which life stage of the host that they attack and in what part of the host they may lay their eggs. Wasps and flies can act as effective parasitoids (Cornell University, n.d.; Hoffman and Frodsham, 1993).


Disease-causing organisms, such as bacteria, viruses, or fungi, can be used to control or eliminate an insect population. Some pathogens have been mass-produced and developed into commercial microbial insecticides to help control insect infestations. Most microbial insecticides must be applied during the correct life stage of the pest (Cornell University, n.d.; Hoffman and Frodsham, 1993). 


Predators of insect pests include arthropods, such as beetles, true bugs, lacewings, flies, midges, spiders, wasps, and predatory mites, which eat or kill the pest. Predators can be specialized in the prey they eat, or be generalists. The risk with using predators as a biological control is that the predator may also prey on other native and beneficial insects as well (Cornell University, n.d.; Hoffman and Frodsham, 1993).

Mechanical Control

  • Physical control involves putting up barriers to prevent an established invasive species from moving into a new area (OMNRF, 2014).
  • Manual control of forest pests includes actions such as hand-pulling, digging, flooding, mulching, or manual removal of nests, eggs, or other lifestages of the pest. As this type of control involves a lot of physical labour, it is most effective for small pest infestations and where other control efforts cannot be used (Wisconsin DNR, 2012).
  • Silvicultural control can include hoeing, cutting, girdling, tilling, or mowing (Wisconsin DNR, 2012).  Trees infested with forest pests can be cut down and their wood can be burned and buried in hopes to slow the spread of an invasive forest pest. Whole logs from trees that have been cut down should not be removed from the area and residues should be destroyed (NRCan, 2013).
  • Prescribed fire as a control for forest pests could be used in rare occasions. Fire could be used in a controlled and closely monitored manner to reduce invasive woody plants. Such fires need to be set under very specific weather conditions to ensure the fire remains contained. Burn permits are required in order to use this method (Wisconsin DNR, 2012). Further, because of the risk involved with using fire, this method is now rarely used.

More Information

Some best management practices for treating invasive pests include the following:

Seek out appropriate treatment strategy

  • When determining how to treat an invasive forest pest, seek out different treatment strategies and methods and determine the one best suited to the situation at hand.
  • Develop a treatment strategy outlining the appropriate steps and methods to control the invasive pest and for monitoring the treatment and its effectiveness. This helps to clarify the control protocol for those administering the treatment and ensures it is efficiently applied and monitored.

Apply treatment during the appropriate time frame

  • To maximize efficiency and cost-effectiveness, the treatment should be applied at the time window indicated to be the most effective. This can minimize the need to reapply or redo the treatment at a different time, helping to save time and money.
  • Treatment of invasive pests should also be carried out before timber harvesting and before using roads and skid trails (Vermont Invasives, n.d.).  Failing to do so can allow for the spread of the invasive to other areas through the movement of infested wood.

Monitor the treatment

  • Monitor the treatment during application to ensure it is applied properly.
  • Properly dispose of any soil, seeds, plant parts, or invertebrates that are found during treatment (Forest*A*Syst, n.d.). Clean off all equipment used during treatment.
  • Reassess the pest and its impacts after the application of the treatment to determine next steps and need for any further treatment.
  • The infested area and its surroundings should also be periodically monitored during and after the treatment to determine treatment effectiveness and to ensure that new infestations do not arise. Monitoring the area around the initial sighting and treatment area can also help to reduce the spread of the pest to another area through early detection.


  • Because forest pests and other invasive species do not respect boundaries, it should be a joint effort between all stakeholders and the public to most effectively prevent and treat outbreaks of invasive forest pests in all areas affected, or in those with potential to become affected.
  • It is imperative that land managers work together so that invasive forest pests can be dealt with in a quick, effective, and collaborative manner. Land owners should work with those adjacent to them to treat and prevent forest pest from entering new areas, establishing, and spreading to other areas.
  • Neighbouring municipalities should also work together to share resources and to effectively prevent and control the entry and spread of invasive pests.
  • As spread of forest pests is facilitated by global trade, travel, and movement of goods from one region to another, provincial, federal, and international cooperation is important in the prevention and treatment of invasive forest pests.
  • Individuals should cooperate with any policies, laws, or regulations pertaining to invasive species management. It is also helpful for individuals to report sightings, to take steps to prevent spread of invasive pests, and to learn about forest pests and their impacts.