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PEST OF THE MONTH Hemlock Woolly Adelgid By Joe Doccola Adelgids are very small piercing-sucking insects that feed on conifers. Some species, such the Spruce Gall Adelgid, produce galls (abnormal growths on tree tissues) while others, such as Hemlock Woolly Adelgid (HWA), produce wax that appears woolly. Adelgids pierce the twigs at the base of the needles and extract vital nutrients from the plant. Hemlock and Spruce tree species are especially susceptible to Adelgids, but many other species also play host to this devastating insect. HWA is unseen with the naked eye and feeds on hemlocks. HWA is an invasive species from Asia that has infested the U.S. East Coast hemlock forest from Maine to Georgia, inhibiting twig growth throughout. It has also recently been found in Michigan and as far west as Kentucky and Tennessee, and is believed to be expanding its range due to changes in climate. HWA has a complex life cycle: its winter generation and spring generation overlap in the spring. It feeds and reproduces during the colder months, going dormant in the summer. Symptoms The earliest visible sign of HWA is the presence of white, cottony masses, usually located on the twigs and at the bases of the needles. Populations tend to be denser in the lower limbs but can be any- where on the tree. Hemlock Woolly Adelgid damage then displays as gradual fading and browning of limbs, often starting at the tips and progressing down the limb, until the limb eventually dies. Symptoms will progress to increased fading, thinning and dying limbs, with die- off beginning at the base of the tree and moving upward. Left untreated, the death of the tree is certain. Treatment Arborjet recommends a trunk injection of imidacloprid. To give the tree a greater health benefit, a follow-up application of ROOT-jet Iron or MIN-jet Iron is recommended — the specific formulation dependent upon soil type. Each product is formulated to supply essential nutrients to support foliar development without added nitrogen, which could exacerbate HWA infestations. When to treat Generally, the best seasons for trunk injection treatments are fall and spring, as uptake occurs when trees are transpiring. The environmental conditions that favor uptake are adequate soil mois- ture and relatively high humidity. Soil temperature should be www.arborage.com Photo provided by Arborjet above 40 degrees Fahrenheit for trunk injection. Hot weather or dry soil conditions will result in a reduced rate of uptake, so trees should be watered if applications are made when soil is extremely dry. If treating trees in the summer, inject in the morning for the quickest uptake. In hemlock, fall treatments coincide with HWA resumption of feeding. Applications of imidacloprid may be applied in hemlock from September through December, as long as soil temperatures are above 40 degrees Fahrenheit. The second window for application is in the spring months, from March through June. Tree health will also affect treatment efficacy, so assess tree health prior to treating. For example, a declining tree (>50% canopy dieback) is a poor candidate for treatment. What to expect after treatment Injection time varies depending on the environmental conditions, tree health and method of application. Uptake time is approximately 15 to 30 minutes for high-volume dosages. Applications made at lower doses may be applied in as little as 3 to 5 minutes per tree. Systemic activity occurs when the imidacloprid moves upward into the foliage from the injection sites. Adelgid mortality occurs after ingestion, generally within 14 to 28 days, and continues for up to two years. Cottony masses remain for some time, but will turn a distinc- tive gray color. Hemlocks respond positively to treatment with a resumption of twig growth. Joe Doccola is director of research and development for Arborjet. He is an ISA Certified Arborist and Plant Health Care specialist with more than 30 years experience in the horticultural and arboricultural field. Arbor Age / October 2012 7 3