By Don Grosman, Ph.D.
With the ever-increasing trade around the world, more and more insects, diseases and weeds are finding ways to come to America. Most travelers do not survive the trip, let alone become established in this new land. Unfortunately, several have found the right conditions (temperatures, moisture, hosts, etc.) to become established, and a few have been able thrive, multiply and have a significant impact on tree health. This article will present some information about five of the more notorious insect pests currently attacking and killing trees in the United States.
Photo courtesy of USDA Forest Service – Region 8 – Southern Archive, USDA Forest Service, Bugwood.orgHemlock Woolly Adelgid
The Hemlock Woolly Adelgid (HWA, Adelges tsugae) is a true bug native to East Asia that feeds by sucking sap from hemlock and spruce trees (Tsuga spp.; Picea spp.). In eastern North America, it is a destructive pest that poses a major threat to the Eastern Hemlock (Tsuga canadensis) and the Carolina Hemlock (Tsuga caroliniana). It was accidentally introduced into western North America from Asia in 1924. HWA was later found in the eastern United States, near Richmond, Va., in 1951. The pest has now been established in 11 eastern states from Georgia to Massachusetts, causing widespread mortality of hemlock trees.
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 anywhere on the tree. Feeding damage results in a 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 move upward. Left untreated, the death of the tree normally occurs within three to four years.
Photo by Dean Morewood, Health Canada, Bugwood.orgAsian Longhorned Beetle
The Asian Longhorned Beetle (ALB, Anoplophora glabripennis) is a destructive wood-boring pest of maple and other hardwoods. ALB was first discovered in the United States on several hardwood trees in Brooklyn, N.Y., in 1996. ALB is believed to have been introduced into the United States from wood pallets and other wood packing material accompanying cargo shipments from Asia. ALB was later detected in Chicago (1998), northern New Jersey (2002 and 2004), Worcester, Mass. (2008), Suffolk Co., Mass. (2010), and, most recently, Clermont Co., Ohio (2011).
Symptoms of ALB infestation are similar to symptoms of many pest infestations, including yellowing leaves, and dieback of branches. Specific signs include bleeding wounds in the trunk or large limb bark, indicating oviposition of eggs. There may also be large (3/8-inch), perfectly circular holes in the trunk or large limbs and frass (sawdust) on the ground near the holes. The beetles themselves may also be visible during mid to late summer months, feeding in the canopy.
Photo by Taylor Scarr, Ontario Ministry of Natural Resources, Bugwood.orgEmerald Ash Borer
Emerald Ash Borer (EAB, Agrilus planipennis) is another exotic beetle that was discovered in southeastern Michigan near Detroit in the summer of 2002. The adult beetles nibble on ash foliage but cause little damage. The larvae (the immature stage) feed on the inner bark of ash trees, particularly green, black and white ash, disrupting the tree’s ability to transport water and nutrients. EAB probably arrived in the United States on solid wood packing material carried in cargo ships or airplanes originating in its native Asia. Emerald Ash Borer is now present in 18 Midwest, Northeast and Mid-Atlantic states, as well as Ontario and Quebec, and has killed upward of 60 million trees in those areas.
EAB larvae live under the bark and feed on the vascular tissues. Larvae create meandering galleries through the phloem, vascular cambium and etch the xylem, effectively girdling the tree. The tree responds by sprouting new (epicormic) branches below the disrupted tissues. Dieback of the canopy is a symptom of EAB larval infestation as many as one half of the branches may die back as infestation progresses. The bark will split over dead vascular tissues, and trees may die within only two years of the onset of symptoms. Extensive woodpecker damage is also a symptom of EAB attack.
Photo provided by Arborjet Inc.Rugose Spiraling Whitefly
Rugose Spiraling Whitefly (RSWF, Aleurodicus rugioperculatus) is a nuisance pest discovered in southern Florida in 2009 on Gumbo Limbo trees. This whitefly appears to have a very broad host range from palms to woody ornamentals and fruits. It is now found along the Atlantic and Gulf coasts, primarily where coconut palms grow. Adult RSWF congregate on the undersides of the leaves to feed and reproduce.
The most noticeable symptoms of an infestation of this whitefly are the abundance of the white, waxy material covering the leaves, and also excessive sooty mold. Like other sucking insects, the RSWF will produce large amounts of “honeydew,” a sugary substance, which causes the growth of sooty mold. The actual effect of an infestation on the health of a plant is unknown; however, whiteflies in general can cause plant decline, defoliation and branch dieback.
Polyphagous Shot Hole Borer
Polyphagous Shot Hole Borer (PSHB, Euwallacea fornicatus) is a new pest in Southern California. This ambrosia beetle drills into trees and brings with it a poperii of fungi (Fusarium sp., Graphium sp. and Acremonium sp.). As of summer 2012, it has been found to attack more than 200 species of trees in the Los Angeles area, including the native Coast Live Oak (Quercus agrifolia) and the California Sycamore (Platanus racemosa), as well as 52 species (about 57 percent) of the most common street trees in the area.
The very small PSHB females (0.1 inches in length) bore through the tree’s bark, creating galleries in the sapwood tissue. They plant the fungus in these galleries, where it grows and spreads throughout a susceptible tree. The female then lays her eggs in these galleries and when the eggs hatch, the larvae feed on the fungus. Symptoms of PSHB attack and fungus infection differ among tree species. Although the PSHB attacks many tree species, it is capable of producing offspring in only 22 (8 percent) tree species. These species are considered true hosts of PSHB, and include Box Elder, Coast Live Oak, sycamore, avocado and invasive plants such as castor bean and tree of heaven (Ailanthus). Some trees seem to suffer mild symptoms like branch die-back, while others are killed outright.
Trunk injection of imidacloprid is recommended for HWA, EAB, ALB and RSWF. TREE-äge* insecticide (emamectin benzoate) is recommended for EAB control. No truly effective treatments are available for extended protection of trees against PSHB. Trials are underway to determine if TREE-äge and other products are effective treatment options.
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 moisture and relatively high humidity. Soil temperature should be 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.
Tree health will also affect treatment efficacy, so assess tree health prior to treating. For example, a declining tree (>50 percent canopy dieback) is a poor candidate for treatment.
Injection time varies depending on the environmental conditions, tree health and method of application.
Don Grosman, Ph.D., is technology advancement manager at Arborjet Inc.
Arborjet’s IMA-jet and TREE-äge are effective using the TREE I.V. system or QUIK-jet micro-injector. The TREE I.V. injects high volumes of product under low pressure, resulting in efficient uptake. The QUIK-jet works best with applications in palms and hardwoods such as ash, maples and oaks, and takes only minutes to apply. Uptake time is approximately 15 to 30 minutes for the high-volume dosages applied by TREE I.V. Applications made at lower doses with the QUIK-jet can be applied in as little as 3 to 5 minutes per tree. Systemic activity of IMA-jet or TREE-age occurs when the active ingredient moves upward into the foliage from the injection sites. Insect mortality occurs after ingestion, generally within 14 to 28 days, and continues for up to 2 years.
* TREE-äge insecticide is a Restricted Use Pesticide and must only be sold to and applied by a state-certified applicator. TREE-äge is not registered for use in all states. Check with your state or local extension service prior to buying or using this product. TREE-äge is registered trademark of Arborjet, Inc.