News from Elsewhere

The following articles will present information on three pests that could find suitable and abundant habitat here if they breach their respective quarantines. The articles were excerpted from the reference(s) cited at the end of each article.

Sudden Oak Death

A phenomenon known as Sudden Oak Death was first reported in 1995 in central coastal California. Since then, tens of thousands of tanoaks, coast live oaks, and California black oaks have been killed by a newly identified fungus, Phytophthora ramorum. On these hosts, the fungus causes a bleeding canker on the stem. The pathogen also infects Rhododendron spp., huckleberry, bay laurel, madrone, bigleaf maple, manzanita, and California buckeye. On these hosts the fungus only causes leaf spot and twig dieback.

In January 2002, the disease was known to occur only in California and southwestern Oregon. As of April 30, 2004, twelve states, Washington, New Mexico, Florida, Louisiana, Georgia, Maryland, Tennessee, North Carolina, Texas, Colorado and Virginia, and British Columbia have positive SOD finds, primarily in garden centers that appear to have received infected plants. The pathogen has the potential to infect oaks and other trees and shrubs elsewhere in the United States and Canada. Limited tests show that many oaks are susceptible to the fungus, including northern red oak and pin oak, which are highly susceptible.

On oaks, cankers are formed on the stems. Cankered trees may survive for one to several years, but once crown dieback begins, leaves turn from green to pale yellow to brown within a few weeks. A black or reddish ooze often bleeds from the cankers, staining the surface of the bark and the lichens that grow on it. Bleeding ooze may be difficult to see if it has dried or has been washed off by rain, although remnant dark staining is usually present.

Necrotic bark tissues surrounded by black zone lines are usually present under affected bark. Because these symptoms can also be caused by other Phytophthora species, laboratory tests must be done to confirm pathogen identity.

In the Eastern United States, other disorders of oaks have similar symptoms. If unusual oak mortality occurs and symptoms do not match these regional disorders, evaluate affected trees for Phytophthora ramorum.

In the USA, sudden oak death is known to occur in forest stands only along the West Coast. However, the fact that widely traded rhododendron ornamentals can be infected with the pathogen and the demonstrated susceptibility of some important eastern oaks make introduction to eastern hardwood forests a significant risk. Early detection will be important for successful eradication. Oaks defoliated early in the growing season by insects or pathogens may appear dead, but leaves usually reflush later in the season. Canker rots, slime flux, leaf scorch, root diseases, freeze damage, herbicide injury, and other ailments may cause symptoms similar to those caused by P. ramorum. Oak wilt, oak decline, and red oak borer damage are potentially the most confusing.

Related publications online:
Sudden Oak Death Pest Alert - USDA Forest Service

Banded elm bark beetle

Scolytus schevyrewi, the banded elm bark beetle (proposed common name), was first collected in insect traps set in Aurora, CO (a suburb of Denver), and Ogden, UT, in April 2003. By the fall of 2003 this bark beetle had been collected in the following states: Arizona, California, Colorado, Idaho, Illinois, Kansas, Nebraska, New Mexico, Oklahoma, Oregon, South Dakota, Utah, and Wyoming. Recent examination of the state insect collection in New Mexico revealed that S. schevyrewi was present in Clovis, New Mexico, as far back as 1998. The beetle was observed attacking and killing drought stressed Siberian elms. The Animal and Plant Health Inspection Service (APHIS), state forestry organizations, and the U.S. Forest Service are currently working together to map out the range and impacts of this exotic bark beetle.

S. schevyrewi is native to Asia, including the countries of China, Kazakhstan, Korea, Kyrgyzstan, Mongolia, Russia, Tajikistan, Turkmenistan, and Uzbekistan. In Asia, hosts for S. schevyrewi include a variety of native elm species, willows, fruit trees such as apricot, cherry, and peach, and Russian olive. In the United States, the banded elm bark beetle has been found infesting and breeding in American, English, rock, and Siberian elms only. The beetle has been collected from broken elm branches, fallen elm trees, stacks of elm firewood, and elm trees stressed by drought. S. schevyrewi also has been reported to be present in trees dying from Dutch elm disease.

The biology of S. schevyrewi is similar to that of S. multistriatus, another exotic bark beetle native to Europe, which is the principle vector of Dutch elm disease in the United States. The banded elm bark beetle completes a generation in two months or less. S. schevyrewi probably completes a minimum of 2 - 3 generations per year in the Denver area. The egg galleries of these two species of bark beetles are very similar. The literature suggests that newly emerged brood beetles of S. schevyrewi have a period of feeding at branch junctions in the canopies of living elms, like that reported for S. multistriatus. This is important because feeding by S. multistriatus on branch junctions in the canopies of elm trees is one mode of transmission of the Dutch elm disease fungus to uninfected trees. BEBB hasn't been shown to spread DED, yet.

Studies of the banded elm bark beetle in 2003 indicate that some brood larvae may burrow into the outer bark of infested elms to pupate and transform into adults. This behavior may explain how this Asian bark beetle was introduced into the U.S. Wood pallets or shipping containers constructed with beetle-infested elm wood, with the bark attached, may have been the original mode of introduction for this bark beetle into the U.S. Insects and disease organisms introduced into the U.S. from other countries may have the potential to alter our natural forest ecosystems and damage ornamental vegetation.

At this time, the banded elm bark beetle appears to pose a moderate risk to elms planted as shade trees or as windbreaks throughout the inland West, particularly during periods of drought. This species appears to be more aggressive than the ubiquitous S. multistriatus. In areas where the banded elm bark beetle has become well established, like Denver, this beetle is much more abundant in dying elms than is S. multistriatus.

Related publications online:
Scolytus schevyrewi Semenov - An Asian Bark Beetle New to the United States - USDA Forest Service

Emerald ash borer

An exotic beetle from Asia, Agrilus planipennis, was discovered in July 2002 feeding on ash trees in southeastern Michigan, in and around Detroit. Larvae feed in the cambium between the bark and wood, producing galleries which soon girdle and kill branches, stems and entire trees. More than 3000 square miles in southeast Michigan are infested and more than five million ash trees are dead or dying from this pest. EAB can attack all species of ash, healthy or stressed, and, young or old.

This exotic insect is also established in Windsor, Ontario, just across the border from Detroit. In 2003, newly established populations were detected in other areas of southern Michigan and Ohio. Infested ash nursery trees have recently been found in Maryland and Virginia.

Related publications online:
Emerald ash borer Pest Alert - USDA Forest Service