Backyard Gardener: Hemlock wooly adelgid an invasive pest
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Hello Mid-Ohio Valley farmers and gardeners! The remnants of tropical storm Fred have brought a lot of rain to the valley. We were pretty dry so the moisture will be used for crop growth both in the farm fields and our gardens. We are also celebrating agriculture at the West Virginia State Fair this week.
I want to invite the public to join our weekly agriculture podcast "Mountaineer Farm Talk" every Friday at 10 a.m. We discuss a variety of topics related to farming, gardening, horticulture and forestry. This week we have Leslie Boggess from the WV Department of Ag discussing the WV Farmers Market Senior Vouchers Program. Join us at https://wvu.zoom.us/j/98991307779.
This week I will discuss a tiny insect is which is posing an imminent danger to hemlock trees in West Virginia, the hemlock woolly adelgid (Adelges tsugae). We have just experienced the devastating loss of thousands of ash trees due to the invasive Emerald Ash Boer, and now this pest threatens our forests here in the Mountain State.
I have had a few calls at the Extension office from land owners wanting to know how to identify this pest and how to save their hemlocks and control this invasive insect.
The hemlock woolly adelgid is a small, aphid-like insect native to Asia, which threatens the health and sustainability of Eastern and Carolina hemlock trees and has the potential to upset entire wildlife habitats.
The Eastern Hemlock (Tsuga canadensis) is one of the most shade tolerant (many have adapted to survive in as little as 5 percent sunlight) and long lived trees in our forests here in West Virginia.
Hemlocks grow on nearly 19 million acres in the Northeastern United States, many reaching well over 100 feet tall and living for hundreds of years. Several wildlife species depend on the environment that exists in hemlock stands.
Hemlocks are considered a foundation species. Foundation species are tree species that define the forest structure and control ecosystem dynamics. Hemlocks commonly grow along headwater streams, greatly influencing stream characteristics like temperature and nutrient cycling.
The hemlock woolly adelgid was first reported in the eastern United States in 1951. Areas along the Appalachian Mountains have experienced significant mortality of eastern hemlock due to this devastating insect. The insect was first reported in West Virginia in the early 1990s and can now be found in 42 counties in the state.
Adelgids appear on hemlock branches and look like tiny cotton balls, averaging approximately 1/16 inch in length because of the white, wool-like substance they produce over their bodies. They feed at the base of hemlock needles and drain the sap causing the needles to fall off, which eventually leads to premature death of the tree.
Adults have a covering of wooly like wax filaments it produces to protest itself and eggs from natural enemies. The best time to see these wooly egg clusters (called ovisacs) is from late fall to early summer.
An unusual life cycle, an abundantly available susceptible host and a lack of natural enemies has resulted in an explosion of woolly adelgid populations in the eastern United States.
The woolly adelgid life cycle is unusual because it feeds during cooler parts of the year and is inactive in the hot summer months. It feeds on the nutrients in the hemlock twigs and also avoids many predators.
The woolly adelgid injures the hemlock by depleting its energy reserves, significantly reducing the tree's ability to grow and produce new shoots. The tree goes into decline, first with a reduced production of shoots in the crown, then needle drop, branch tip dieback and thinning of the foliage.
The eventual decline and death of the hemlock tree is a slow process, ranging from two to 12 years. West Virginia's state parks and forests will be at risk for severe damage if they are not controlled. The insects can be spread by birds and other animals.
USDA scientists have researched and released a biological control in the fight against the hemlock woolly adelgid. Since 2003 Laricobius nigrinus, a small beetle which eats this pest, has been used to help with control. Over 400,000 Laricobius nigrinus beetles have been released across the eastern U.S., from Georgia to Maine.
Every fall and winter, the Laricobius beetles feed on adelgid egg clusters and adults. These beetles can destroy or disturb 80 percent of egg clusters, drastically diminishing the size of the winter generation. This predator is native to western North America.
However, Laricobius is only active during the fall and winter. Unfortunately, the adelgid produces another generation in the spring. The nymphs which hatch from this generation begin feeding on hemlock sap with no predators in sight.
Frequently checking hemlocks for infestations is essential to prevent adelgid populations from building to damaging levels. Chemical control is the most common management technique. Insecticidal soap or horticultural oil sprays are used to treat small trees.
Larger trees can be treated with a systemic product that is absorbed by the plant and moved throughout its tissues. Bayer 12 Month Tree and Shrub Insect Protection Landscape Formulaç and Bonide Annual Tree and Shrub Insect Controlç are products home owners can use to treat hemlock infested with the woolly adelgid. They both contain the active ingredient imidacloprid. This systemic insecticide dissolved in water moves down through the soil, where it is absorbed by the roots. Once absorbed, it moves up through the tree to control this pest for about one year.
Contact me at the Wood County WVU Extension Office 304-424-1960 or e-mail me at jj.barrett@mail.wvu.edu with questions. Good Luck and Happy Gardening!