Hemlock Woolly Adelgid

Preventing an Infestation

The best way to manage an infestation in a larger forest property is to take steps to stop the arrival of Hemlock Woolly Adelgid in the first place, or at least to significantly limit its impact should it arrive.

There are only a few direct actions that can be taken prior to the arrival of HWA to fight against it before it enters your hemlock forest. In larger or denser forests, thinning of hemlocks can help to decrease the spread of an infestation if the pest does arrive. This allows you to prioritize trees that may be of higher value as either ornamental or historical landmarks. Active monitoring of your forest is also very important to catch possible infestations early. This should be done twice a year, preferably in late March and early November, although some variability on these dates is fine. Monitoring should cover at least ten percent of your forest, ideally in a random distribution, with more coverage yielding better results. Cleaning forestry equipment and other tools or items that have been transported from other locations before their use in your forest is an important step to prevent HWA from arriving at your property. You should also work to clear invasive species, as this is a significant source of stress for hemlocks and damages overall forest health.

In areas where there is a very high likelihood of you may choose to treat high value trees with insecticide prior to the arrival of HWA, but this is generally not recommended as it can result in tree or environmental damage unnecessarily. Beyond these steps, it is important to avoid making changes, significant or otherwise, to your hemlock forests, as this can create environmental stresses on the trees that makes them more vulnerable to HWA.

Report an infestation

IF YOU HAVE FOUND AN INFESTATION, PLEASE REPORT IT TO THE MAINE FOREST SERVICE HERE.

After reporting the infestation, you should work either with the Forest Service or a commercial arborist to discuss a management plan for your property. Approaches will vary depending on how much of your property is infested, as well as other considerations for environmental value and possible impact. Make sure you have a good understanding of the infestation and possible solutions so you can reach a successful conclusion.

Chemical-Free Management

Most chemical-free management options for Hemlock Woolly Adelgid on a forest scale are similar to those that exist for small scale management, with one notable exception: biological control.

Basic management for infestations generally begins with trimming infested branches and burning or treating them on site to limit the spread of HWA on your property as well as to other locations. If you have large trees with major infestations, you should also consider removing the tree entirely so that it does not serve as a reservoir to enable future spread of the pest. If not already completed, this could also be a time to conduct thinning in your forest to help decrease the spread of HWA to other hemlocks.

Finally, biological control is a possible solution for HWA management of a larger forest plot. This involves the release of predator beetles that will help to control local HWA populations. Since the beetles may take some time to have an impact, this approach is likely best paired with a combination of other management approaches like trimming, thinning, or insecticides since these will help until biological control can be established. A beetle release is expensive and will require coordination with the Maine Forest Service, so this step should only be undertaken with proper consultation. A beetle release on your property will also help provide a larger range of biological control for other locations where HWA may be spreading.

Chemical Management

Chemical management is possible for larger hemlock forests infested with Hemlock Woolly Adelgid, but it is not a large scale solution. However, depending on your management approach, you can also use insecticides in conjunction with trimming and thinning. Foliar sprays or insecticidal soaps are useful for hemlocks that can be fully coated, usually ones that are below 30 feet in height. This should be undertaken with the help of a professional to get best results and avoid negative environmental impacts. Soil or trunk injection of insecticides can also be used, though in this case it should be reserved for high value or ornamental trees as otherwise the expense and difficulty will outweigh the benefits. Injection may also be used for high value trees that have not been infested if you have a large infestation on your property already.

rehabilitation

If you have already lost part of your forest as a result of Hemlock Woolly Adelgid, you can take steps to restore and rehabilitate the forest to allow it to continue as a healthy ecosystem. The most important approach is restoration with native species such as Eastern White Pine, which is ecologically similar to the Eastern Hemlock. This allows some of the ecosystem services provided previously by hemlocks to continue, as well as prevents the spread of invasive species that may otherwise take over the cleared space. Restoration could be encouraged through forest thinning and prescribed burning or direct seeding and planting of nursery seedlings. Appropriate fencing and protection is important to allow these young trees to flourish. DO NOT replant with monocultures, as this will limit forest health and increase susceptibility to other pests or diseases. Instead, focus on a variety of native species that can help replace the environmental and esthetic value of lost hemlocks. Consultation with professionals and other forest managers can help inform on appropriate native species for this approach.

Invasive control is also key to maintain forest health as hemlocks are lost, since weakened forest ecosystems will be more susceptible. This includes direct invasive removal as well as continued monitoring to ensure that new growth is not occurring.

In areas with a large deer population, deer browse protection should be applied to young trees, otherwise any replanting efforts will be ineffective. This can be achieved through fencing or mesh protection of seedlings, as well as other approaches. Discussion with management professionals is important to determine a cost-effective and appropriate solution.

Of course, the ideal situation would be a reintroduction of hemlocks, but this should only be applied if the right amount of monitoring and protection can be applied to ensure success. This could be achieved through chemical controls or through the establishment of successful biological controls like predator beetles. Research is also being put towards possible hybridization of hemlocks with species that are more successful at surviving HWA, though this has not been successful as yet. Most likely, this is not a viable solution currently but hopefully in the future reintroduction will be an effective rehabilitation method for HWA-damaged forests.