Other Insects and Diseases
There are many other insects and diseases that threaten Pennsylvania’s forests. Some species are native while others are non-native invasive species.
Forest tent caterpillar
The forest tent caterpillar (PDF) (Malacosoma disstria Hubner) is a native insect of North America, and can sometimes be a serious defoliator of deciduous hardwood trees, principally:
This insect is usually kept in check by a variety of native parasitoids and diseases, but does occasionally reach outbreak levels every seven to 10 years. During outbreaks, forest tent caterpillar populations will rise to high levels for one to three years and then crash, once parasitoid populations catch up.
The forest tent caterpillar does not make a silk tent in trees.
Eastern tent caterpillar
The eastern tent caterpillar (Malacosoma americanum Fabricus) is a native insect of North America and is often noticed in early spring by its construction of silk tents in cherry trees.
While it occasionally reaches outbreak levels and defoliates a variety of deciduous hardwood trees (especially black cherry and other cherry species), it is not normally thought of as a significant pest and control measures are not usually warranted in forest situations.
Homeowners can easily control the eastern tent caterpillar in ornamental cherry trees by removing the caterpillars in the silk tents or removing the egg masses from the twigs before they hatch in April.
Asian longhorned beetle
The Asian longhorned beetle (PDF) (Anoplophora glbripennis) is a potentially severe insect pest for a wide range of North American deciduous trees, especially maple species. Asian longhorned beetle has not been found in Pennsylvania. It’s introduction into the United States has been confined to a handful of locations, including Chicago IL, Worcester MA, New York NY, northern New Jersey, Bethel OH, and Toronto, ON. In each instance, eradication programs have managed to stop the spread of the insect outside of the initial infestations.
The DCNR Bureau of Forestry, Pennsylvania Department of Agriculture, and the USDA conduct surveys for this pest in Pennsylvania.
Exotic bark beetles
Some exotic bark beetles (PDF) (Family Scolytidae) are destructive non-native pests of conifer and some broadleaf trees in North America, and there is a persistent threat of new species to be introduced. Programs to monitor for the presence of these insects in Pennsylvania are ongoing.
Southern pine beetle
Southern pine beetle (PDF) (Dendroctonus frontalis Zimmermann) is an important native bark beetle pest in the United States. While it prefers the southern ellow pines such as loblolly (Pinus taeda L.) and shortleaf (Pinus echinate Mill), it can attack any pine species.
While this insect is typically thought of as a southern United States problem, it has been found in Pennsylvania in the past and has caused tree mortality in Delaware, New Jersey, New York, and Connecticut. The DCNR Bureau of Forestry is currently monitoring for this pest with a system of lure traps.
Fall cankerworm (PDF) (Alsophila pometaria Harris) feeds on a variety of broadleaf tree species but is not considered a significant forest pest. As with many native insects, it is kept in check by predators, parasitoids, and tree defenses, but does occasionally reach outbreak levels causing noticeable defoliation. Outbreaks of fall cankerworm do not last more than one to two seasons.
Elongate hemlock scale
Elongate hemlock scale (Fiorinia externa Ferris) is a serious non-native invasive pest of hemlock (Tsuga spp.) in Pennsylvania. It is not uncommon in eastern Pennsylvania to find hemlock trees infested with both elongate hemlock scale and hemlock woolly adelgid.
The DCNR Bureau of Forestry has a continuous monitoring program for elongate hemlock scale, and has taken control measures on state forests and parks when necessary.
Cherry scallop shell moth
Cherry scallop shell moth (Hydria prunivorata Ferguson) is a native insect that feeds on black cherry (Prunus serotina), an important commercial species in Pennsylvania. Periodically, populations reach outbreak levels, but crash after three or more seasons, mostly due to parasitism from a specific species of parasitoid wasp. The most recent cherry scallop shell moth outbreak started in 2015 and is continuing to its third season.
Beech bark disease
Beech bark disease (PDF) is a fungal pathogen spread from the invasive beech scale insect (Cryptococcus fagisuga Lindinger). Beech scale transmits two funguses when feeding on the trees, leading to cankers and eventually death. The disease has killed large numbers of beech (Fagus grandifolia Ehrh) in North America.
Oak wilt (Ceratocystis fagacearum) is a fungal pathogen primarily of oaks in the red oak group. From the moment that symptoms are observed trees can succumb and die rapidly. Leaves turn brown and fall, working from the top of the tree downward.
The pathogen can be spread by feeding insects, transmission from root to root, and mechanically from improperly cleaned pruning tools or chainsaws.
Thousand cankers disease
Thousand cankers disease (PDF) is a complex that is caused by a fungus (Geosmithia morbida), which is in turn spread from tree to tree by an insect vector, the walnut twig beetle (Pityophthorus juglandis). This disease is a threat to black walnut (Juglans nigra), which is highly susceptible.
The DCNR Bureau of Forestry has monitored for thousand cankers disease and the walnut twig beetle for several years. To date, thousand cankers disease is not established in Pennsylvania.
Armillaria root rot
Armillaria root rot is a fungal disease that affects hundreds of species of woody plants, including forest and shade trees. Armillaria is not one single species but refers to over 30 different species. The fungus primarily spreads through root-to-root transmission, and death of the tree being either sudden or gradual.
Sudden oak death
Sudden oak death is caused by the fungal pathogen Phytophthora ramorum, attacking oaks, Rhododendron, huckleberry, and other trees and shrubs. The DCNR Bureau of Forestry has been conducting surveys for sudden oak death since 2006, with no positive detections to date.
White pine decline
Serious decline is now occurring on white pine (Pinus strobus), with twig dieback and seedling/sapling mortality being observed. The pathogens Canavirgilla needle cast, Lecanosticta acicula, Diplodia tip blight, and other needle disease fungi are all associated with the decline.
Fabrella needle blight
Fabrella needle blight (PDF) (Fabrella tsugae) is a leaf disease of eastern hemlock. Damage from the disease is significant during prolonged cool wet periods in the spring into the summer. Some twig and branch dieback in the lower crown may be evident but usually is not lethal to the tree. However, when other stress factors such as hemlock woolly adelgid or drought come into play, significant dieback and mortality is likely.
Butternut canker is caused by a fungal pathogen (Sirococcus clavigignenti-juglandacearum) and is a severe threat to butternut (Juglans cinerea) in the United States. Infection from this pathogen leads to cankers on branches, twigs, stems, and buttress roots on butternut trees, which girdle the tree, leading to dieback and death.
Bacterial leaf scorch
Bacterial leaf scorch is associated with Xyella fastidiosa, and has been observed on oak, elm, sycamore, mulberry, red maple, and sweetgum, and others. Pin oak and other red oaks are especially susceptible.