The Hemlock Woolly Adelgid.

There is an alien here in the southern Appalachians and it has the potential to do massive harm to our native forests. It is a small, fragile insect that doesn't really even look like an insect, but a large infestation of them can be devastating to even our most massive hemlocks. The insect is the Hemlock Woolly Adelgid (Adeleges tsugae) and in the eastern United States it has a very large food supply and no natural predators.

The Hemlock Woolly Adelgid, or HWA, is native to Japan and was first brought to the western U.S. in the 1920's on nursery stock. In the western states, HWA is not a major problem, as their hemlocks show some resistance and there are natural predators that feed on the adelgid. It was first seen in the eastern U.S. in the Washington DC. area in the 1950's. Eastern and Carolina hemlocks show little to no resistance and there are no natural predators in the east: the results in Virginia alone have been devastating. The HWA can only survive in the eastern U.S. in its wingless stage. The winged stage requires a particular spruce as a host and since none exist in the eastern U.S, its movement has been relatively slow. Adelgid needs to be carried by birds, the wind, of humans. It is likely that we humans have spread it much faster than birds or wind, probably on nursery stock. Currently, HWA has spread as far north as New England and as far south as Georgia. If left unchecked, the HWA could kill the vast majority of Eastern and Carolina Hemlocks in the years to come.

The Eastern Hemlock (Tsuga canadensis), and the Carolina Hemlock (Tsuga caroliniana), are very important components of the natural forest ecosystems of the eastern United States. Hemlocks can regenerate under a very dense forest canopy and can survive in the understory for decades waiting for a space to naturally open in the canopy by a fallen of dead tree. When given the opportunity, they will grow extremely quickly to claim their space alongside the dominant trees of the forest. This is a unique trait that most other species do not possess. Most other trees either need full sun to regenerate, of if they can start from seed under a thick canopy, they need an opening very soon or they will not survive.

The Hemlock Woolly Adelgid is here to stay. so either we find a way to manage it or we face the reality that our hemlock populations will be decimated by this invasive exotic insect. There are really only

three ways to manage this type of a pest. First, we could let natural selection work things out, and someday long after we're gone the hemlock might come back. Second, we can use biological control by releasing a predator either from Asia or from the western U.S. to help keep the populations of HWA from exploding. Or third, by chemical control, the HWA is relatively easy to control on a tree by tree basis with properly used chemical pesticides, easy to do in your hall acre yard, difficult in a large forest.

In Great Smoky Mountains National Park, there is an ongoing management plan to help control HWA. Park Officials have been releasing a specialized predator beetle (Sasajiscymnus tsugae) from Japan that prefers to feed only on Adelgid. Since 1995, there have been releases of this beetle in fifteen Eastern states including North and South Carolina. There are other predator beetles from China and British Columbia that also show promise as predators and they may be used in future releases. It will take several years before we know how effective these predators will be at controlling Adelgid, but in a large forest, these predators are our best hope for minimizing large outbreaks of this invasive pest.

On a smaller scale, such as with individual trees around houses, these insects are controlled fairly easily by pesticides. Small trees can be sprayed with insecticidal soap or horticultural oil. For larger trees it is best to hire an arborist to apply a systemic pesticide, typically the chemical imidacloprid, either into the soil or directly into the stem of the tree. This systemic application works well because the chemical is taken into the tissue of the tree and the chemical affects only insects that feed on the tree. Although this treatment does involve the use of chemical pesticides, if done properly, it can be a safe way to save trees from this fatal insect problem. The Great Smoky Mountains National Park is also treating a large number of its old growth hemlocks with systemic pesticides.

Whether you have a yard with one precious hemlock or you're lucky enough to have many acres of them, you can do your part in saving this majestic tree by treating it for HWA. There are many professional arborists that can help you to determine which method works best for your particular situation.

REFERENCES AND RESOURCES:

http://www.ivasive.org/hwa/sasajiscymnus.cfm

http://na.fs.fed.us/fhp/hwa/

http://www.caes.state.ct.us/FactSheetFiles/Entomology/fsen012f.htm

http://www.saveourhemlocks.org/index.shtml

http://www.ces.ncsu.edu/depts/ent/notes/O%26T/trees/note119/ note119.html

Ron Busch is a Certified Arborist with the International Society of Arboriculture, a NC certified pesticide applicator and holds a BS in Forestry with an Urban Forestry specialization from University of Wisconsin at Stephens Point. He is a self employed arborist living in Asheville, NC. He can be contacted via email [e-mail].