HWA Management For Landowners
The first step for landowners is to determine if an HWA infestation is present on your property. This involves scouting for HWA, making sure to look carefully at several twigs on all sides of a tree and surveying trees throughout each stand. For help identifying hemlock trees or HWA, you can use our Hemlock and HWA Identification Guide.
Management strategies are only necessary if you have HWA on your property. If you do not detect HWA, there is no need to treat your trees, but do continue to check on your hemlocks a few times a year to catch new infestations early. Early infestations are easier and less expensive to manage than well-established infestations.
Management using biocontrol: Please note that all of our biocontrol release sites are located on publically-owned lands (DEC lands, State Parks, National Forests, etc.) and that our biocontrol bugs are not available for use on private lands at this time.
If you find HWA:
If you have found HWA on your property, don’t panic! There are several options for management and treatment. Since it takes HWA several years to kill a tree, you have time to prepare and prioritize your management goals. In many cases trees with thinned canopies are able to be brought back to full health.
While we recommend consulting with a licensed arborist and pesticide applicator, there is an effective product that landowners may purchase for treating trees themselves. Selecting the right treatment plan can impact treatment efficacy and cost, so it is important to consider several options to find out what will work best for you and your trees.
Treatment Timing:
Spring is the best time of year to treat HWA-infested trees, however you can also treat trees in the fall season. Since the products used to treat HWA are systemic, they must be taken up by the tree. This process is most effective in the spring during the tree’s biggest growth push or during the smaller growth push in the fall. Additionally, treatments during these seasons should be made while soils are moist, not during drought conditions.
Visit our Treatment Options page for a list of available treatments for HWA.
HWA Treatments for Landowners
The only treatment method for HWA that is available to private landowners without a certified pesticide applicator license is a soil drench of Imidacloprid. Dinotefuran cannot be applied by private landowners. Soil drench involves applying a product with Imidacloprid as the active ingredient directly to the mineral soil surrounding an individual hemlock tree. The amount of product applied to each tree will be dependent on the tree size.
You can find instructions for soil drench applications of Imidacloprid from our partners at the University of Georgia Warnell School of Forestry and Natural Resources by clicking the button below:
Pesticide Treatment of HWA:
There are two systemic pesticides that are used to treat HWA in New York: Imidacloprid (active ingredient) and Dinotefuran (active ingredient, brand names Safari™ 20SG and TransTect™).
Imidacloprid:
Imidacloprid is a great tool for treating trees since it is effective for up to seven years following application and is relatively inexpensive. However, it is relatively slow-acting and can take up to a year to become fully effective in the canopy. While it is active in the tree, the tree’s HWA infestation will die, and HWA will be prevented from re-colonizing the treated tree, as individuals will die as they begin to feed.
The only treatment option available for use without a Certified Pesticide Applicator certification is soil drench of the imidacloprid, which can be purchased at your local garden supply store or online. You can visit our Imidacloprid Information page for more information on Imidacloprid, including its fate in the environment.
Dinotefuran (Safari™ 20SG and TransTect™):
Dinotefuran is another tool for ridding a tree of an HWA infestation. It is fast-acting in the tree, quickly reaching the canopy (within two to three weeks), but it is only effective in the tree for about a year following application. Application with Dinotefuran is most useful for older trees or trees with severe crown decline that may not survive another season of HWA infestation. Use of Dinotefuran is only allowed with a pesticide applicator certification and only as a basal bark application.
After Treating
Applications of Imidacloprid are typically effective for up to seven years, but it is important to continue to keep an eye on your trees to be certain infestations have not reestablished. The best way to check that trees are remaining healthy following treatment is to keep an eye on new growth each season in the late spring to early summer. Between May and June, hemlocks typically have bright, lime green buds at the tips of branches that is easy to discern from the darker green of previous years’ growth. Healthy trees should have ample new twig growth, indicating low impact from HWA infestations. If your trees have been treated be sure to check the upper crown for new growth; tree recovery after treatment starts at the top and lower branches may still show little to no signs of recovery.