PROTECTING HEMLOCKS ON YOUR LAND
DO i HAVE HEMLOCK TREES?
If you own forest land there is a very good chance there are hemlocks on your property. Hemlocks are most often found in moist, shady areas of the forest along streams and creeks, but they also grow on ridgetops and hillsides. Near water they may form groves where they are the most common tree, while they often grow alone or in small clumps in dryer parts of the forest. Hemlocks are also common yard and landscaping trees, so you might not have to go farther than your back yard to find one.
Range of Eastern hemlock in Kentucky
Are my trees at risk?
Whether you own forest land or have hemlocks in your landscaping, your trees are vulnerable to infestation by hemlock woolly adelgid. With the exception of an isolated population in and around Mammoth Cave National Park in west central Kentucky, virtually all of the counties within the hemlock's native range have already been classified as infested. Even if your trees have not yet been affected, they are very unlikely to avoid eventual infestation. Infested trees can die in as few as four years.
What can I do?
Until biological control methods (introduced predator beetles) are better proven and more widely available, chemical insecticides are the most effective way to save trees. The most commonly used chemical treatment is an insecticide called imidacloprid. You can purchase imidacloprid yourself under a number of brand names in tablets, powders, and liquid solutions.
With proper precaution and attention, you can treat your trees yourself. Both infested and healthy hemlocks can be treated with imidacloprid at relatively low cost. Using the retailer, products, and application rate we recommend below, a small tree (4" diameter) can be treated for as little as 8 cents, medium trees (20" diameter) can be treated for as little as 98 cents, and very large trees (35" diameter) for $2.16, offering protection that can last for four years or more*.
*A note about application rates, duration of protective effect, and uncertainty: the insecticide imidacloprid is most commonly used in row crop agriculture. Its use against invasive forest pests like the hemlock woolly adelgid is relatively new. As a result, we do not have perfect knowledge about the best way to use imidacloprid to treat hemlocks. There are guidelines, but recommended best practices may change as we continue the work to save hemlocks. The manufacturer of the product we recommend, Prime Source Imidacloprid 2F, recommends that between .1 fl oz and .2 fl oz of insecticide be applied per inch of tree diameter. However, research has suggested that there may be a different optimum application rate connected to tree size. Below, you will find recommendations based on research from the University of Georgia that recommends specific application rates tied to specific tree diameters. There is also uncertainty about how long a single treatment will protect any given tree. Ideally, trees should be monitored regularly after treatment. A further complication is that no more than 25.6 fl oz of Prime Source Imidacloprid 2F (or .4 pounds of imidacloprid in any formulation) can be applied to a given acre in a single year, according to federal regulations. This may be an obstacle if you have dense stands of many hemlock trees. In this case we recommend treating your largest and/or most infested trees in the first year, and treating remaining trees in the out years.
As of June 2018, the most cost effective treatment option for landowners with modest numbers of hemlocks is soil drench with Prime Source Imidacloprid 2F. The 2.15 gallon size of this product can be purchased from Seed World and shipped to most locations in Kentucky for roughly $120. But other formulations and vendors can be found. The soil drench application method is fairly straightforward (see the video above from the Lexington Herald-Leader); the procedure is as follows:
With proper precaution and attention, you can treat your trees yourself. Both infested and healthy hemlocks can be treated with imidacloprid at relatively low cost. Using the retailer, products, and application rate we recommend below, a small tree (4" diameter) can be treated for as little as 8 cents, medium trees (20" diameter) can be treated for as little as 98 cents, and very large trees (35" diameter) for $2.16, offering protection that can last for four years or more*.
*A note about application rates, duration of protective effect, and uncertainty: the insecticide imidacloprid is most commonly used in row crop agriculture. Its use against invasive forest pests like the hemlock woolly adelgid is relatively new. As a result, we do not have perfect knowledge about the best way to use imidacloprid to treat hemlocks. There are guidelines, but recommended best practices may change as we continue the work to save hemlocks. The manufacturer of the product we recommend, Prime Source Imidacloprid 2F, recommends that between .1 fl oz and .2 fl oz of insecticide be applied per inch of tree diameter. However, research has suggested that there may be a different optimum application rate connected to tree size. Below, you will find recommendations based on research from the University of Georgia that recommends specific application rates tied to specific tree diameters. There is also uncertainty about how long a single treatment will protect any given tree. Ideally, trees should be monitored regularly after treatment. A further complication is that no more than 25.6 fl oz of Prime Source Imidacloprid 2F (or .4 pounds of imidacloprid in any formulation) can be applied to a given acre in a single year, according to federal regulations. This may be an obstacle if you have dense stands of many hemlock trees. In this case we recommend treating your largest and/or most infested trees in the first year, and treating remaining trees in the out years.
As of June 2018, the most cost effective treatment option for landowners with modest numbers of hemlocks is soil drench with Prime Source Imidacloprid 2F. The 2.15 gallon size of this product can be purchased from Seed World and shipped to most locations in Kentucky for roughly $120. But other formulations and vendors can be found. The soil drench application method is fairly straightforward (see the video above from the Lexington Herald-Leader); the procedure is as follows:
- Mix Imidacloprid 2F with water in a container according to the ratios in Table 1 below. Always wear gloves when handling imidacloprid, and avoid spilling to minimize non-target exposure. Mix the chemical at least 100 feet away from any streams and do not treat any trees that right next to streams or that have close root contact with streams. Imidicloprid is really bad for aquatic invertebrates (insects), and a spill would be extremely damaging. Almost any hand carried container (like a large plastic jug) will do, but you will want a something that makes it easy to measure water and chemical when mixing, and that is an adequate size for the number of trees you wish to treat at one time. A measuring cup or bottle is also useful to accurately measure the volume of imidacloprid. The Kentucky Division of Forestry mixes chemical in a large jug, and then pours some of that mix into 48 oz. Nalgene water bottles which make it easy to measure and apply the correct amount to each tree (described below).
- Measure the diameter of your tree. There are specialized tools such DBH tapes, biltmore sticks, and calipers available for this purpose, but any flexible measuring tape will do. If you don't have a diameter tape, meaure the circumference of the tree with your tape at ~4.5 feet above the ground and divide by 3.14. This number is your tree's diameter.
- Kick or rake back the "duff" within 18 inches of the trunk all the way around the tree. The goal is to expose an area of mineral soil through which the tree's roots will take up the insecticide. Organic matter such as recognizable needles, leaves, and twigs, as well as decayed or partially decayed plant and animal material will prevent optimal uptake.
- Apply the chemical to the mineral soil exposed in step two with the volume of Imidacloprid 2F/water mixture listed for the diameter of your tree in Table 2. Record the tree size and/or volume of imidacloprid applied so that you stay below the .4lbs (25.6 fl oz) per acre threshold.
- Replace the duff layer.
- If you are treating in an area with lots of hemlock trees you may want to mark treated trees with a spot of tree marking paint so that you can keep track of your work and monitor recovery, decline, and/or new infestations.
Table 1. Mixing table for Imidacloprid 2f
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Table 2. Application volume per tree
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Commercial hemlock specialists in Kentucky
If you have many acres of forest land it may not be feasible to treat all of your trees yourself. The following are firms who are available to treat hemlock trees on private land for a fee. The list is not complete, nor is it an endorsement of any listed business. If you or someone you know represent a business that offers this service, please contact us to be included in this directory.
Barnwell Forestry treats hemlocks on private land on a per acre basis. Contact forester Mike Silliman at (828) 506-1519 or [email protected].
