FAQ

There are three categories to take into account when trying to distinguish between eastern and Carolina hemlocks. (1) Habitat: eastern hemlocks will grow near water and on shady slopes, while Carolina hemlocks grow in drier conditions on high, rocky ridges; although in some places both species can be found growing together. (2) Morphology: eastern hemlock needles grow in a flat plane along the branches, and can grow to 175 feet tall, while Carolina hemlock needles are ‘whorled’ around the branch in a circle, and typically only reach heights of around 75 feet. (3) Cones: eastern hemlock cones are about half the size of Carolina hemlock cones. For more information, see our Identification Guide.

Hemlocks are the most shade tolerant tree in North Carolina. They are a major driver of ecosystem processes due to the micro-climate they create under the shade of their massive branches. Along streams, hemlocks physically shape the waterways by holding stream banks in place, they keep the water temperature cool and consistent under their shade, and they make more water available to watersheds due to their slow rate of transpiration. In forests, they create specific habitats for hundreds of species of birds, mammals, plants, insects, and salamanders, many of which are rare and at risk. For more information, see our page The Importance of Hemlocks.

Hemlocks are dying because of an invasive insect pest called the hemlock woolly adelgid (HWA). HWA was introduced to eastern North America from Japan in the early 20th century, and is now rapidly spreading throughout the native range of hemlock. It began to impact trees in North Carolina in the early 2000s. HWA attaches itself to the base of the hemlock needle and feeds on the tree’s stored nutrients and starches. Over time, the tree begins to lose its needles, decreasing its ability to photosynthesize. The tree declines and eventually dies in as little as four years after infestation. For more information, see our page Hemlock Woolly Adelgid.

Planting hemlocks is an excellent method of conserving them. In a residential or commercial setting, hemlocks are are still a great choice for many of the same reasons they have historically been so popular to plant, including for their aesthetics, privacy and the cooling effects of the shade they provide. However, please ensure that they are the native species, i.e., eastern hemlocks or Carolina hemlocks. Please also be vigilant and look for HWA, and treat with insecticides at the first sign. They will probably find their way to your tree. See our page Where to buy hemlocks for a list of local nurseries that sell native hemlocks.

HWA is a tiny insect (roughly the size of the period at the end of this sentence), and it can be difficult to see with the naked eye. It is most visible during the winter and briefly during the late spring, when it has its signature waxy wool coat, resembling white, woolly puff balls at the base of each hemlock needle. For more information, see our page titled Hemlock Woolly Adelgid.

HWA is immobile for most of its life. However, there is a small period of time right after it hatches from the egg when it can be transferred from tree to tree. This is called the “crawler” stage. When it’s in the crawlers stage, it can be passively distributed many ways such as by wind or by birds who have landed on an infested tree and carry crawlers to another hemlock. Transplanting of infested trees can speed up their spread.

Multiple agencies and organizations throughout the range of eastern hemlock are responding to the crisis with a multi-pronged, integrated approach. None are a stand-alone solution, and instead work together to form a comprehensive plan for hemlock conservation. These methods are:

• Chemical control: This is a short-term, but sure-fire way to protect an individual tree. Hemlocks can be treated with a systemic chemical insecticide that spreads through the whole tree and lasts for 5-7 years. For more information, see our page titled Chemical Treatment under the Solutions tab.
• Biological control: This is the effort to establish a natural predator/prey balance that will keep adelgid populations at a level that hemlocks can tolerate. The most widely used species is the Laricobius nigrinus beetle, which has been well established in some areas that HWA has spread, particularly in Western North Carolina. Other beetle and fly species have also been approved as biocontrols for HWA. However, it is still too early to rely on these predators to keep HWA populations in check. For more information, see our page titled Biological Controls under the Solutions tab.
• Silviculture: This consists of programs working to determine forest management practices that can positively impact the health of hemlocks in the face of HWA, for example, how to manipulate forest structure to provide the best growing conditions that support hemlocks to withstand HWA . For more information, see our page titled Silvicultural Strategies under the Solutions tab.
• Genetic: These efforts include breeding native hemlocks that are resistant to HWA, and work to preserve genetic diversity for reforestation. For more information, see our page titled Genetic Research under the Solutions tab. 

There are a number of ways to get involved. These include treating your trees, spreading the word about what is threatening hemlocks, participating in volunteer workdays to perform treatment, monitoring for biological controls, or taking part in research. 

Folks in North Carolina can contact HRI directly for advice and to learn about upcoming events. Folks in other states can contact their state agencies responsible for invasive species management such as the state forest service, division of forestry, department of natural resources, etc., or the Cooperative Extension service to see what type of opportunities for involvement are happening in their area and to seek advice or support for treating areas. For more information, see pages under our ‘Resources’ tab.

It is reasonable to assume that if a hemlock in North Carolina has not been chemically treated, it is infested with HWA. Tell-tale signs of HWA include:

• Round, white puff balls along the underside of a branch at the base of the needles
• Loss of needles and graying foliage, giving the trees a distinctive gray appearance
• Graying, dead or dying branches starting at the base of the tree and moving upwards
• The persistence of dead, fine, branching twigs, indicating needles were lost recently and quickly

In North Carolina, there are two options to get your trees treated: either hiring a professional or doing the treatment yourself. The cost for hiring a professional can vary depending on each business. You can find information about hiring a professional and a list of some providers in the Western NC region on our Hemlock Treatment Providers page.

Treating your hemlocks yourself can be quite simple and inexpensive. All you need is a little bit of simple equipment and the insecticide. Depending on the product you use and the size of the tree, the cost of the insecticide to treat hemlocks that are still fairly healthy can be less than $5. Hemlocks with worse health may be up to $25-50 or more per tree to treat. For more information, see our page titled Chemical Treatment for Landowners under the Resources tab.

Systemic insecticides work by entering the tree tissue and spreading through the whole tree. When the insect feeds on the tree tissue, it ingests the insecticide and dies. Hemlocks are commonly treated systemically for HWA with imidacloprid and dinotefuran. A systemic treatment with a product containing imidacloprid can last 5-7 years with one simple application to the roots or the trunk of the tree. The drift risk is minimal, and it is very effective. See our Chemical Product Comparison Chart under Step 5 of our Chemical Treatment for Landowners page for more information on different forms and brands of systemic insecticide for HWA.

Contact insecticides work by covering the insect and smothering it. Horticultural oils and insecticidal soaps are two common contact insecticides used for HWA. Contact insecticides only work to control HWA if you can cover every branch where HWA is present, particularly the underside of the branches, and must be done once or even twice a year to control HWA. HRI doesn’t use contact insecticides in our work, so we don’t have detailed guidance on using those, but some people prefer them as a less toxic alternative to systemics. There are some resources online, particularly on some state cooperative extension websites, about spraying hemlocks with oils or soaps.

Dinotefuran products, such as Safari 20SG, when applied properly and according to the label, may be able to get into the tree’s system in a matter of a few weeks. Imidacloprid products take longer, several months even up to a year, to build up in the tree tissue and begin killing hemlock woolly adelgid.

That being said, the time it takes for insecticide to start killing the adelgid will vary based on the individual tree and environmental conditions at the time of application, which influence how quickly the tree is transpiring and moving fluids (and the insecticide) through its vasculature. The insecticides will be transported through the vasculature and distributed to the tree’s “storage cells” where they will persist for a period of time. Dinotefuran typically protects the tree for 1-2 year. Imidacloprid can protect the tree for 5-7 years.

However, even after the insecticide gets into the tree, you should not expect to see change right away. Hemlock woolly adelgid is mostly dormant in the summer; they go through a summer dormancy period called aestivation where they are not actively feeding. Once the adelgid nymphs “wake up” and start feeding on the starches stored in the tree tissue, they should also take up the insecticide, and consequently die. They will not begin feeding until temperatures begin to cool off in October-November. Please also be aware that even after the adelgids die, they will remain attached to the branches for several more months. Even the white “wool” that protected the previous generations’ eggs may persist on the branch for a number of months.

After control has been achieved, it can take several years for the tree to begin to look visibly different. After all, hemlocks are slow-growers, but eventually the foliage on treated trees should become full and thick in areas where it had thinned out but the branches were still alive. Dead branches will not produce new needles.

We recommend you wait until winter or early spring (December through March) in the year following the treatment to inspect the branches for new, fresh, woolly “cotton balls” where the needles attach to the twig. If the adelgid nymphs begin feeding and there is no pesticide present, they will begin to fatten up into adults and will start putting on the white “wool” for which they are named. This is when they are easiest to observe. If you do not see the white wool by March, or only find a couple of “cotton balls”, then the treatment likely worked. You can also look for new foliage in the late spring, early summer. Healthy trees should have lots of new, bright green needles at the tips of the branches in the spring.

Most situations require only imidacloprid. However, if the tree has declined in health significantly or the HWA infestation is extremely heavy, an initial treatment with a dinotefuran-based product might yield a better outcome. Dinotefuran is a faster-acting, albeit shorter-lasting active ingredient. You should follow up in a year with an imidacloprid treatment to further protect your tree.

Soil application methods like soil drench and CoreTect tablets are simple and efficient for landowners to do themselves. Stem-based (trunk) application methods are recommended for trees within 10-20 feet of a water source, or when there are roots of flowering plants where the chemical is applied that might take up the chemical and translocate it to pollen or nectar. Using a soil application in these situations could pose a risk to non-target organisms like stream invertebrates and pollinators.

Basal bark spray is one stem-based method; another is stem injection. Basal bark spray can be done by a landowner or professional; however, this method requires care and vigilance not to increase the chance of drift or off-target exposure when doing a bark spray. We recommend contacting a professional to perform stem injection due to the expense of the equipment and the difficulty of ensuring a correct application. See our page titled Hemlock Treatment Providers to find tree care specialists in Western North Carolina that treat hemlocks.

Occasionally generic imidacloprid products and dinotefuran products can be found at a local hardware store. Most big box stores carry more expensive versions of imidacloprid. These “general consumer” products can be useful for treating one or two hemlock but become expensive for treating more trees than that. In the case where you have many hemlocks to treat, generic imidacloprid products are more economical. You can refer to our product comparison chart to see relative prices. Generic imidacloprid products and dinotefuran products are easily found at many online pesticide retailers and can be found in Western North Carolina at some specialty ag and farm stores.

In the Southern Appalachians, you can treat hemlocks almost any time of year, as long as the trees are actively transpiring. This occurs throughout the year unless the soil is too dry or, conversely, too saturated, the air too hot or humid, or the ground is frozen. That being said, we prefer to conduct hemlock treatments when the trees are most actively transpiring to facilitate efficient uptake of the chemical pesticides. Therefore, we do most of our treatments in the fall and spring when hemlocks are most active.

The two main chemicals we use, imidacloprid and dinotefuran, are made to be safer than some other insecticides for humans and consequently other vertebrates. This means it is a low-risk option for pets and other animals. Animals would have to be exposed to large, concentrated quantities of the chemical, relative to their size, to reach toxic levels and have adverse effects. Proper application methods can be used to minimize this risk even further, such as performing targeted applications utilizing optimized dosing strategies, in order to avoid using more chemical over a larger area than is necessary.

HWA do not have their classic “woolly coat” during certain months of the year and therefore can be very difficult to see without magnification. In our region, if you haven’t treated your hemlocks with insecticide, you will likely see the HWA “return” when they begin to put on wool as the year progresses. Cold winters and late freezes can contribute to natural mortality in HWA populations, but HWA populations in Western North Carolina have been pretty consistent over the past few years.  It is unlikely that they are completely gone without insecticide application.  

You must obtain permission from the landowner or management agency to perform any treatments. Public lands with hemlocks may have a management plan for their hemlocks, which could include chemical treatment, biological control, or both. You should not take it upon yourself to apply pesticide on public land, and if biological control is being pursued in the area you are concerned about, applying pesticide could interfere with those objectives.

The extent of these management activities depends on the resources and capacity of the managing agency, and HRI works on many state and some federal lands to implement their HWA management.  If you see hemlocks that you are concerned about on public lands, you can reach out to the managing agency and express your concern and desire that the hemlocks be protected. They may be able to tell you what HWA management work they have been doing in the area you are concerned about. If the land you are hiking on is owned by a land trust or private landowner, we recommend you reach out to the landowner and find out if they are aware of the HWA on their hemlocks and the options available to protect the trees.

Additionally, you can advocate to state and federal policy makers on behalf of hemlocks and include information about the particular areas and trails that you are concerned about.  Elected officials often respond to the loudest voices and personal stories.

Once you have treated the hemlock trees on your property, fill out our Hemlock Treatment Follow-up Survey. If you have previously attended one of our treatment workshops, you will receive one of our signs for no cost. Otherwise you can purchase a sign for $8. You can pick up the sign at our office or we can mail it to you for an additional $10 to cover the shipping. We are only able to provide one sign per landowner. See our Events page for upcoming treatment workshops.

Unfortunately, HRI does not treat hemlocks for private landowners. However, we are here for support every step along the way. Our Information for Landowners page will guide you step-by-step if you wish to treat yourself, or our Hemlock Treatment Providers page offers a great first step if you wish to hire someone else to treat. We are always available by phone call or email if you have any questions at any point in the process.

Laricobius nigrinus beetles are established and spreading on their own in Western NC, so it’s not really necessary for individuals to release that species. Additionally, there is not really an accessible commercial source to buy the beetles. You may already have Laricobius beetles on your hemlocks or the beetles should eventually come to your property naturally. However, at this point we can’t rely on them to protect and restore the health of the hemlocks alone. While biocontrol is a hopeful long-term solution along with other IPM approaches, right now the most reliable way to protect your hemlocks from HWA is with chemical treatment.

If you would like to monitor your own infested trees for Laricobius beetles, please see our page on beetle monitoring at home.

Although there have been some biological control failures, there are dozens of other successes. The Laricobius beetles are one of these. These beetles were subjected to approximately 10 years of studying before release, and it was determined that they are obligate feeders of HWA. This means that we see the Laricobius populations disappearing once the HWA is gone–while they may be able to feed on other adelgid species, they are dependent on HWA in order to reproduce, and thus cannot survive without them.

Since the beetles do not ingest any part of the hemlock, they will rarely directly be killed by the insecticide, but they will lose their food source as the HWA die. This is a very delicate balance we work to keep in our treatment areas. For private landowners, in most circumstances, we suggest chemically treating any tree you do not want to risk losing or see decline in health.