Hemlock Woolly Adelgid
What is Hemlock Woolly Adelgid?
Hemlock Woolly Adelgid, abbreviated as HWA, is an invasive insect from Japan that feeds on Eastern Hemlock trees. HWA is a death sentence to hemlocks, taking between 4 and 10 years to fully defoliate and kill the tree entirely. HWA can be identified by the white, woolly ovisacs that they produce on the underside of branches at the base of needles. These ovisacs will be most prevalent in winter months when adult adelgids are reproducing. HWA reproduces asexually, with one adelgid having the capacity to produce up to 175 eggs, meaning that one adelgid can cause reinfestation. Hemlock infestation can change the landscape of a forest entirely in as few as 20 years. The most important option in your toolkit as a landowner is chemical treatment.
Chemical Treatment Options
Chemical treatment for Hemlock Woolly Adelgid is done with neonicotinoids, a class of pesticide formatted for insect biology.
Imidacloprid; Example(s): Imicide HP, Lesco Bandit 2F
Imidacloprid products are the long term option for chemical treatment, providing between 5 and 7 years of control over HWA. These products take 12 to 18 months to fully translocate into the tree. These products are able to be applied via either basal bark spraying or trunk injection. These are also the cheaper of the two chemical treatment options available.
Dinotefuran; Example(s): Safari 2G
Dinotefuran products are a faster acting, shorter lasting chemical treatment option. These products take around 2-4 weeks to enter the trees canopy and establish control, where they will then last 12-18 months. If your trees are particularly unhealthy we may recommend a combination of dinotefuran and imidacloprid treatments to get HWA under control as fast as possible to give time for long term chemical treatment to establish control. Dinotefuran treatment is more expensive than imidacloprid treatment, so it is often reserved for severely declined trees.
Alternate Treatment Options
Non-pesticide options for treatment are often cheaper and seen as safer, however the frequency of treatment may be a concern for some landowners
Horticultural Oils; Example(s): Bonide, LESCO, Monterey Insecticidal Soaps; Example(s): Natria
One alternative option to pesticide usage is horticultural oils or insecticidal soaps, which is often a cheaper option than pesticide treatment. Treatment via horticultural oil/insecticidal soap involves spraying the full length of the tree to smother any adelgids on it. Due to the method of treatment, there is the chance for some adelgids to survive, leading to necessary and frequent reapplication (often multiple times a year).
Grant Based Programs:
Our grant based treatment program has been a large part of our crews work since our program began in 2018. Since then Ottawa Conservation District (OCD) has been able to treat 140,000+ hemlock trees with grant funding. The size of property covered by grant treatment ranges drastically, so over time the crew has gotten familiar with how to approach parcels ranging from less than an acre to over 200 acres.
Michigan Invasive Species Grant Program (MISGP)
This grant is what our crew has spent the most time working out of, covering the treatment of 65,000 hemlock trees from Ottawa to Mason County from 2022-2024.
Great Lakes Restoration Initiative (GLRI)
GLRI has been helping to fund the crew since it’s beginnings in 2018, with the first itteration helping to provide treatment to just over 28,000 hemlock trees in West Michigan from 2018-2021. Starting last year our crew has resumed treatment under a new itteration of this grant and is using it to help treat in Mason County.
Landscape Scale Restoration (LSR)
LSR is currently helping us provide treatment to select lakeside areas in Ottawa County, including our recent treatment of the Rosy Mound Natural Area’s new expansion.
For Hire Program:
Our for hire program is an at cost but not for profit program to provide interested landowners with treatment if they are located in grant covered areas. We provide quotes free of cost and are happy to work with you to find a treatment plan that fits your budget.
The first step in our process for at cost treatment is generating a quote for the projected cost of treatment. This involves the crew collecting some general information about the property such as average tree sizes, density of hemlock stands, and presence of small trees. If you have questions, concerns, or would like to be present for this process you may be, however you are not required to be present for it. After this visit a quote will be generated and shared with you, if you would like to modify which trees are being treated or with what chemical they are treated this is an option, you would just need to communicate as such and a new quote will be provided.
After a quote is agreed upon the crew will then come out to survey the property. FOR SMALLER PROPERTIES; If your property is small enough for us to think it’s manageable within a day, you will be notified that you are on our Survey&Treat List. All this means is that your property will not be surveyed in the winter, but rather it will be surveyed on the day of treatment. While out they will collect data for every hemlock tree on the property that will be recieving treatment. This includes tagging the trees for ease of identification during treatment, collecting size data, taking GPS points for each tree, and various tree health metrics. Our surveying season typically takes place from November through April each year. Once our treatment season begins in May we will not be conducting any more surveys for the year.
Our crew treats hemlocks with two chemicals, the most prominent is Imidacloprid which is a long lasting insecticide that can either be basal bark sprayed or injected into the trunk of the tree. Imidacloprid products offer 5 to 7 years of control over HWA when applied at the rates that our program uses. However, imidacloprid products take about 12 to 18 months to gain control in the tree, making them the best option for trees that are relatively healthy. If your trees are particularly declined we have the option to treat with a faster acting chemical, Dinotefuran.
Additional Resources:
For information regarding Hemlock or HWA identification, Michigan’s quarantine of Hemlocks, or maps detailing the spread of HWA: michigan.gov/HWA
Homepage for SaveMIHemlocks: savemihemlocks.org
Outside of Ottawa County? Find out what CISMA covers your county here: michigan.gov/invasives/take-action/local-resources/view-cisma-locations-as-a-list