Hemlock Woolly Adelgid
reported by David Barnes -- August 5, 2005

Talk By Hortoculturalist Beth Hawke at Grey Towers
USFS Center in Milford, PA. on July 21, 2005


I attended this workshop on the woolly adelgid, a tiny insect about the size of the head of a pin which has caused widespread decline and death of hemlock trees, from southern New England to the Smoky Mountains. Hemlock mortality rates of 70% to over 80% in this region are common, with only western and northern areas of the Appalachians, Catskills, Great Lakes and Adirondacks still free from the pest. The hard winters in these areas in recent years are the main reason that infestation has not spread further -- the adelgid cannot survive sustained temperatures of below 5 degrees Fahrenheit.

Grey Towers Horticulturist Beth Hawke led a discussion on how to recognize a woolly adelgid infestation and what landowners can do to protect and prevent further decline of hemlock stands, which are still present in our region, some still in a healthy state depending on the specific location.

Hemlocks are an important component of the forest ecosystem, comprising about one-fourth of our forests. This tree prevents erosion along rivers and provides winter shelter and food for wildlife.

The woolly adelgid sucks sap from the young twigs, causing the needles to discolor and drop prematurely. The loss of new shoots and needles seriously impairs tree health, with defoliation and tree death occurring within several years.

The attached web page was distributed, describing the history of the problem and showing with words and pictures how to recognize an infestation from the white cottony sacs on the underside of hemlock twigs and needles. Also, a map was passed around at Beth’s talk – I have a copy – showing the extent of the infestation up and down the Eastern Seaboard as of 2004, with the NY State infested area clearly including both Delaware and Sullivan Counties.

Even though many of us in the Beaverkill area so far have not seen evidence of a woolly adelgid infestation, Beth informs me that the map is accurate. Once the pest is found in one location in the county, it is on the infested list. No county has ever been removed once it is listed as infested because there are many hemlocks in those counties and Beth cautions that viewing from the ground does not mean that the tree is free of the adelgid. So once it is there it is usually never completely eradicated. Beth told me that our county may not be heavily infested yet, but there is a big possibility that there is still some adelgid nearby. I have heard other reports that the pest has been detected at Frost Valley. So while it may not be widespread, it should probably be considered as in the area and a viable threat.

So as the July 21 workshop made clear, careful monitoring is the key, together with treatment once the pest has been located and identified. Treatment includes use of horticultural oil or insecticidal soap, applied by spray from truck or backpack tanks, or the pesticide Merit. Unfortunately, there is no one-time preventative treatment prior to infestation since no treatment effect lasts more than a year or so and must be re-applied annually. So frequent monitoring, especially in the spring and fall, is the only answer with treatment recommended only when the pest is discovered.

The safest for both environment, applicator and wild life is the horticultural oil or soap. These treatments only "smother" the soft body insects (the adelgid) leaving the other beneficial insects. These are also safe around water systems.

Merit, near streams and water sources should be used only as an injection into the trunk of the tree and done by certified tree arborists. For those hemlocks away from a direct water source, the "over the counter" Merit applied as soil drenching around the tree could work. Merit, in tests, does not appear not to travel far in the soil. So it is a safe treatment, but remember that it is a pesticide.

The most expensive treatment is the Merit trunk injection, which costs from $200 to $300 per tree.

Beth Hawke has kindly offered to answer further questions, so please let me know if any of you would like to know more.

Above, in addition to a link to a printable text, you will find two links to the US Forest Service with more info about the Woolly Adlegid, and photos.

David Barnes
August 5, 2005



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