Department of Environmental Protection

New Jersey Forest Service

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Forest Health Program in New Jersey

The New Jersey Forest Service surveys and monitors New Jersey's forests both from the ground and the air for various forest health threats. While most insects and diseases are part of the natural ecosystem, the NJFS is mainly concerned with forest health threats that are invasive, spread quickly, or have the ability to affect otherwise healthy trees. Often the pests and diseases of concern are non-native and introduced to our forests accidentally. Without native predators, these pests have the potential to cause indiscriminate, accelerated, and widespread tree mortality.

Details
The spotted lanternfly (SLF) was detected in NJ in the summer of 2018 in Warren, Mercer, and Hunterdon Counties. Currently, SLF is detected in 19 counties.

SLF is native to China, Bangladesh, and Vietnam. The first North American detection was in Pennsylvania in 2014, and has since been detected in Virginia, Delaware, Maryland, Connecticut, West Virginia, Ohio, and New Jersey. The SLF is a leaf hopper insect that feeds on the phloem of trees and plants. The SLF excretes honeydew (a sticky, sugary waste product) onto anything that is below the insect, including plants, young trees, shrubs, sidewalks, outdoor furniture, etc. In large quantities, honeydew facilitates the growth of black sooty mold that blocks photosynthesis on trees and plants. Copious amounts of honeydew can cause dieback or tree/plant mortality. In agriculture, extensive SLF feeding also causes reduced yield in crops and black sooty mold on produce reduces their marketability.

SLF has a wide host range that includes over 70 different trees, shrubs, vines, and plants. However, it has a strong preference for the tree of heaven, also called ailanthus. Immature SLF are often found feeding on young growth, or new branches because the tissue is softer. However, as they mature into adults, they can be found at the base of the tree or feeding on the trunk. SLF can also be found feeding on maple, black walnut, grape vines, and multiflora rose.

SLF, contrary to its name, is not a fly but in fact a type of planthopper. Although SLF are able to fly, they more often jump or glide as modes of transport. SLF most effectively spread to new areas by hitchhiking rides from infested areas. Therefore it is imperative for anyone traveling in and out of known SLF areas to check their vehicles, goods, etc., for any life stages of SLF to prevent the further spread to new areas.

Susceptible Species
Prefers the invasive “Tree of Heaven,” but makes use of over 70 different plant species including fruit trees, ornamental trees, woody trees, vegetables, herbs, vines, and agricultural crops

Signs of Infestation
Any life stage of the insect is visible feeding on plants, sooty mold, heightened activity from wasps, hornets, ants, and bees

Affected Areas
Atlantic, Bergen, Burlington*, Camden*, Cumberland, Essex, Gloucester*, Hudson, Hunterdon*, Mercer*, Middlesex, Monmouth, Morris, Passaic, Salem*, Somerset*, Sussex, Union, and Warren* Counties

*Counties under State Quarantine

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Details
Beech leaf disease (BLD) was confirmed in New Jersey in the summer of 2020 in Bergen and Essex Counties.

BLD was first detected in North America in Northeast Ohio in 2012. This was a mysterious disease that could not be identified. However, in July 2020, researchers discovered a nematode associated with BLD. The nematode, Litylenchus crenatae mccannii, damages leaf tissue, which causes leaf discoloration and eventual leaf and bud necrosis. After several years of infection, defoliation, dieback, and eventual tree mortality occurs. Smaller, understory beech trees appear to be the most susceptible, succumbing to BLD within 1-5 years, and larger, overstory beech trees succumbing within 6-10 years. BLD has been spreading rapidly since its initial detection in 2012, has since been detected in Pennsylvania, New York, New Jersey, Connecticut, Rhode Island, West Virginia, Massachusetts, and Ontario, Canada.

Researchers and scientists are still learning about BLD, and so there is currently no cure or treatment for BLD. However, reporting new detections can help better understand its most current distribution and track the BLD progression and movement. If you suspect BLD, please contact the NJFS Forest Health Program at foresthealth@dep.nj.gov or 609-292-2532.

Susceptible Species
American, European, and Oriental Beech

Signs of Infestation
Dark banding on the leaves visible on green and brown leaves, leaf edges can start to curl and become leathery in texture, leaf necrosis, thinning crown from the bottom up.

Affected Areas
Bergen and Essex Counties.

More information

Details
Southern pine beetle (SPB) is considered a native insect in New Jersey and was reported as causing damage in southern New Jersey in December 2001. SPB is often present in endemic (low) levels, successfully attacking weakened and stressed pine trees. However, there are also times when SPB populations reach epidemic (high) levels and they are able to successfully attack healthy pine trees. When SPB populations reach epidemic levels, they have the ability to cause significant damage across its range. It is one of the only native bark beetles that can attack healthy trees, where the adult beetles cut off water and nutrient supplies to trees by boring through the bark and creating S-shaped galleries in which they lay their eggs.

The historic native range of SPB includes the southeastern US and parts of Central America, but over the last decade, SPB populations have started to move north. In 2014, SPB populations were found in Long Island, NY causing extensive pine mortality. Through insect trapping, SPB have been detected in Connecticut, Rhode Island, and Massachusetts, the furthest north of its range in history.

Preventing SPB populations from reaching epidemic levels is the most effective method at preventing widespread SPB induced tree mortality. Some prevention actions include:

  • Continual monitoring and surveying of SPB activity and suppressing SPB spots while small to prevent larger SPB outbreaks.
  • Removing weakened and stressed trees that serve as the initial breeding sites for SPB can also prevent SPB populations from establishing.
  • Maintaining healthy pine stands that are better able to defend themselves from SPB attack
  • Encouraging or planting appropriate pine species for the site, so growing the “right tree in the right spot”

Susceptible Species
SPB attacks all species of pine including pitch, shortleaf, Virginia, white, loblolly, and red. To a lesser extent, SPB can attack Norway Spruce, red spruce, and Eastern hemlock.

Signs of Infestation
Pitch tubes, exit holes, yellow and browning crowns, S-shaped galleries under bark

Affected Areas
The southern half of the state has been affected by SPB, however SPB have been detected in traps statewide

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Details
Gypsy moth was first discovered in New Jersey in 1920 and continues to be present in the environment. Fortunately, annual monitoring, suppression programs, and several established biological controls help keep gypsy moth populations in check.

The gypsy moth is native to Europe and was introduced to North America in 1869 in Massachusetts by a scientist, E. Leopold Trouvelot, who was hoping to use gypsy moth caterpillars for silk production. The caterpillars accidentally escaped his property and soon began spreading and infesting surrounding areas. Gypsy moth is currently established from Maine to Virginia and as far west as Wisconsin and Minnesota.

The gypsy moth larva causes the most destruction, feeding on leaves from over 500 different species of trees and plants. The larvae feed on leaves from May to June, and although healthy trees can survive a single year of defoliation, several successive years of heavy defoliation can result in tree decline and mortality. The gypsy moth population in New Jersey is influenced by the presence of the biological controls, Entomophaga maimaiga and Nucleopolyhedrosis virus (NPV). E. maimaiga is a fungus that infects and kills gypsy moth caterpillars, thriving during wet years. NPV is a naturally occurring virus that is most effectively transmitted between caterpillars when gypsy moth populations are high. Although there are additional natural controls that feed on gypsy moth, E. maimaiga and NPV are specific to gypsy moth and are the most effective at impacting gypsy moth populations.

Gypsy moth populations are generally cyclic, peaking every 5-10 years, and are able to increase more rapidly during dry years when E. maimaiga is scarce. In 1981, New Jersey suffered the worst gypsy moth defoliation, impacting over 800,000 acres. Although gypsy moth populations eventually started to decline, populations began to increase again in 2005 – 2007, increasing from 42,000 acres to 324,000 acres respectively. Suppression programs are in place to supplement natural controls during peak gypsy moth years in order to prevent another devastating gypsy moth defoliation event, like the one that took place in 1981. Currently gypsy moth populations are low, but are monitored annually to track their population trends.

Susceptible Species
Prefers oaks and but also attacks many deciduous trees and shrubs

Signs of Infestation
Presence of any life stage of the gypsy moth (adult moth, caterpillar, or egg mass), defoliation, oval egg masses, caterpillars

Affected Areas
Statewide

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Details
Hemlock woolly adelgid (HWA) was detected in NJ in 1978 in Burlington County and is currently found statewide. The heaviest of HWA infestation occurred in the mid to late 1990’s, causing widespread hemlock mortality, and destroying the majestic hemlock forests that once existed along streambanks and hillsides. The impacts of this outbreak are still evident today, where hardwood species have filled in where hemlock forests once existed. Today, individual surviving hemlock trees, or small groups, can still be found scattered across the landscape, and it is hopeful that these will serve as the seed source for future hemlock forests. Nearly all hemlock in New Jersey, approximately 25,000 acres, have been infested with HWA to some extent.

HWA is native to east Asia, and was first discovered in the eastern United States in 1951 near Richmond, Virginia. HWA is a small, soft-bodied insect that feeds on the sap of young branches. In the Northeast, all HWA are females that reproduce parthenogenically. HWA has a complex life cycle, involving three generations per year. One is a winged generation that does not survive in the Northeast, presumably because the spruce host required is not available here. The two other generations are wingless and are so small they are difficult to see with the naked eye. It is the third generation that develops a white, cottony covering, that makes them more visible on the underside of hemlock branches during the late fall and winter.

Biological controls have been released to help control HWA populations, starting in 1998. These predacious insects include Sasajiscymnus tsugae, Scymnus sinuanodulus, and the most recent Laricobius nigrinus in 2005. Cold winter temperatures, pesticide treatments, and host tolerance, also contribute to help protect hemlock trees from HWA infestation.

Susceptible Species
Eastern hemlock

Signs of Infestation
Small white woolly cotton-like balls on the underside of hemlock branches, branch dieback, crown thinning

Affected Areas
Statewide

More information

Details
After overwintering in the soil beneath the host tree, moths emerge in May and June to lay eggs on the tree's needles. By mid-summer, the larvae hatch and eat notches out of the needles.

Susceptible Species
Pine species

Signs of Infestation
Brown needles, defoliation

Affected Areas
Ocean and Eastern Burlington Counties

Details
The emerald ash borer (EAB) was detected in NJ in 2014 in Somerset County, and has since been confirmed in 17 counties in the state.

The EAB is native to Asia, and was first detected in North America in 2002 in Michigan and has since been detected in 35 US states and 5 Canadian provinces. EAB is an invasive and destructive pest, responsible for killing hundreds of millions of ash trees in the US. Adult beetles lay eggs in bark crevices, and larvae then burrow under the bark and feed on the cambium, cutting off water and nutrient transport within the tree.

Systemic pesticide treatments are effective at protecting individual trees, and should be applied by a licensed pesticide applicator. Systemic treatments are most effective when applied to healthy trees, prior to or soon after EAB infestation, so that the pesticide can be effectively circulated throughout the tree.

Biological controls that specifically feed on EAB, have also been released in the US in areas impacted by EAB. NJ started its biocontrol release program in 2016 and continues to release EAB biocontrols annually. The biocontrol insects include tiny wasps that parasitize either the EAB egg or EAB larva. Biocontrol efforts are a long-term management strategy and unfortunately will not protect the current ash populations that exist today. Biocontrols first need to build their populations, which can take several years, and the hope is that the next generation of ash trees will be better protected from EAB infestation.

Susceptible Species
White ash, green ash, black ash, pumpkin ash

Signs of Infestation
D-shaped exit holes, woodpecker flecking on bark, larval galleries under the bark, branch and crown dieback, epicormic sprouts on trunk or base of tree

Affected Areas
Statewide

More information

Details
The Asian longhorned beetle (ALB) was detected in New Jersey in 2002 in Hudson County. In 2004, additional ALB populations were detected in Middlesex and Union Counties. However, as a result of an aggressive and successful ALB eradication program, in 2013, NJ deregulated the ALB quarantine zone, and no ALB have been detected in the state since.

The ALB is native to eastern China and Korea, and was first discovered in North America in 1996 in Brooklyn, NY. ALB has since been detected in additional locations in New York, Illinois, Ohio, Massachusetts, New Jersey, and most recently in South Carolina in 2020.

ALB feed on over a dozen different trees, their most preferred being maples, willows, ash, and poplars. The female beetles chew holes in the bark where they lay their eggs. After hatching, the young larvae feed on the cambium layer of the tree, the living tissue under the bark responsible for transporting nutrients and water throughout the tree. The larvae then bore deep into the tree where they eat and create tunnels through the tree’s heartwood. The effects of ALB feeding on trees can be seen 3-4 years after infestation with branch dieback and leaf discoloration. Infested trees will eventually die approximately 7-12 years later.

Susceptible Species
maple, willow, poplar, ash, horsechestnut/buckeye, elm, birch, golden raintree, London planetree/sycamore, katsura, mimosa, and mountain ash (Sorbus sp.)

Signs of Infestation
Adult ALB, 3/8" exit holes, oozing sap, sawdust, branch dieback

Affected Areas
Eradicated from Hudson, Union, and Middlesex Counties

More information

Details
Although the origin of sudden oak death (SOD) is still unknown, its detrimental impacts on North American oak species suggest the pathogen is non-native. SOD is a fungal pathogen that was first discovered in California in the mid-1990s and then in Oregon in 2001. SOD is responsible for the mortality of millions of coast live oak and tanoaks in California and Oregon.

SOD not only infects oak trees, it can also infect shrubs such as rhododendron and camellia. In addition, there are numerous plants that are asymptomatic carries of the SOD pathogen, which also contributes to the unknown spread to susceptible hosts, such as oak trees.

Susceptible Species
75 Species including many oaks

Signs of Infestation
Brown leaves, large bleeding cankers

Affected Areas
Not yet found in NJ

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Details
Although bacterial leaf scorch (BLS) is considered native to NJ, it was first observed causing tree damage and mortality around 1985 in the southern half of the state, mainly affecting trees in the Red Oak family, such as Northern red oak, pin oak, and scarlet oak. Today, BLS can be found statewide, affecting landscape and street trees as well as those growing in forests.

BLS is a bacterium that is transmitted to healthy trees by leafhoppers and spittlebugs moving from asymptomatic herbaceous plants, such as goldenrod, blackberries, and clover that harbor the bacteria. BLS clogs the trees vascular system responsible for transporting water and nutrients throughout a tree. BLS infected trees will have leaves that have a scorched appearance along the leaf margin. The junction of scorched tissue and green tissue is often yellow or halo-like, one of the identifying features of BLS. In NJ, BLS leaf scorch symptoms become visible in early to mid-August, and is predominately found on red oaks, although it can be detected in other species including sweetgum, elm, and maple.

There is no cure for BLS, however, BLS is a slow tree killer, often taking 10 or more years for an infected tree to succumb but causing gradual canopy decline and dieback over that time. Although antibiotic trunk injection treatments are available to treat BLS symptoms, these treatments must be done on an annual basis and treatments are most effective when done either prior to or soon after infection.

A look-a-like is oak wilt, which has not yet been detected in NJ. See oak wilt for more information.

Susceptible Species
Red oak family (Northern red, pin, scarlet, willow, black, and Southern red), maple, sycamore, elm.

Signs of Infestation
Brown discoloration along leaf margins in August/September.

Affected Areas
Statewide

Details
BBD was detected in New Jersey in 1935, and has impacted American beech trees and forests in the northern half of the state. Although low populations of beech scale have been found in the southern part of the state, the Neonectria fungi have not yet been detected in South Jersey.

Beech bark disease (BBD) is a disease-insect complex between the fungi (Neonectria faginata and N. ditissima) and the beech scale insect (Cryptococcus fagisuga), native to Europe. When the beech scale feeds on the beech trees, it creates a tiny wound that allows the Neonectria fungi to enter and infest the tree. BBD was accidentally introduced to Nova Scotia in the 1890s on an ornamental beech imported from Europe, and by the 1960’s, BBD was well established in the New England states.

The Neonectria fungi develop small, red perithecia, or fruiting structures, that often grow in a circular pattern. The fungi also cause the infected areas to callous, causing a raised or sunken circular callouses that are visible on the trunks of infected trees. The beech scale insect is almost microscopic in size, but it forms a woolly, white coating on the outside of its body, which makes them more visible, especially when there are numerous scale insects infesting a tree. The beech scale insects tend to congregate in bark cracks or areas where the bark is rough, but they can also establish on smooth parts of the bark as well.

Although there are no effective treatments for BBD, researchers have found American beech trees that exhibit resistance to BBD. These trees are tested for resistance then grown in orchards to serve as future sources of seeds for American beech restoration efforts.

Susceptible Species
American Beech Signs of Infestation Sparse foliage, woolly beech scale insects, small red fungal fruiting bodies, round sunken or raised callouses

Affected Areas
Northern New Jersey

More information

Details
Oak wilt is a fungus that causes rapid mortality in oak trees around July - September. Oak trees in the red oak family are more susceptible than those in the white oak family, but both can be infected with the fungus. Red oak trees can die within weeks or months after infection, whereas white oak trees die after a year or more. Oak wilt has not yet been detected in NJ, but has been detected in neighboring states including New York and Pennsylvania.

The oak wilt fungus is spread in two ways, 1) by sap-feeding insects or 2) by underground root grafts. The fungus is able to stick to the bodies of insects that feed on infected trees and then feed on healthy trees. In areas with known oak wilt infection, pruning of oak trees is discouraged during the summer and early fall months when sap-feeding insects are active and can transmit oak wilt when feeding on the wound created at the pruning site. The fungus is also able to move from tree to tree via underground root grafts. For this reason, trees infected with oak wilt often follow a concentric patter of spread.

Oak wilt is very difficult to identify based on trees symptoms alone, because there are other insects, pathogens, and factors that can cause oak leaf discoloration and rapid tree death. The most effective method to confirm oak wilt is through laboratory testing.

Although there is no treatment for oak wilt, it has successfully been eradicated from areas when identified and addressed early. Eradication efforts include the removal and proper disposal of known infected trees in addition to a buffer of asymptomatic trees. In addition, the root systems of the buffer trees removed must be severed or killed to prevent further spread to adjacent oak trees.

In NJ, a common look-a-like is bacterial leaf scorch (BLS). See BLS for more information.

Susceptible Species
Oak Wilt affects both Red and White oak species

Signs of Infestation
Leaf discoloration in July - September, rapid tree mortality, Fungal mats, bark cracking

Affected Areas
Not yet found in NJ

More information

Details
Larvae feed on the bottom of oak leaves, leaving only a leaf skeleton of veins behind. Repeated defoliations may affect vigor or kill the tree.

Susceptible Species
Red and white oaks

Signs of Infestation
Skeletonized or transparent leaves, defoliation starting in upper crown, larvae feeding on leaves

Affected Areas
Northern New Jersey

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Details
Thousand cankers disease (TCD) is a disease-insect complex between a fungus (Geosmithia morbida) and the walnut twig beetle (WTB) (Pityophthorus juglandis), believed to be native to the western states. Although WTB and Geosmithia are found in western walnut species, it mainly affects trees that are already under stress or declining. However, in black walnut, an eastern species, TCD successfully infects healthy trees, causing cankers, dieback, and eventual tree death.

Black walnut trees planted in western states are susceptible to TCD, and it was in Oregon and Utah where walnut decline was first observed in the 1990s. However, it was not until 2007 when Geosmithia was identified as the causal agent of the walnut decline. TCD has not yet been detected in NJ, however, the closest known detections are in Pennsylvania and Maryland.

The disease-causing fungus (Geosmithia morbida) is transmitted into the phloem of the tree by the walnut twig beetle (Pityophthorus juglandis) as it constructs its galleries. Cankers develop around the galleries as a result of the fungus and coalesce to girdle the branch or stem. The cankers are usually small in size, no larger than the size of a quarter. It takes thousands of cankers to cause tree mortality, which is where the name comes from.

Susceptible Species
Black walnut

Signs of Infestation
Branch dieback, epicormic sprouts on trunk or base of tree, many small cankers on branches and bole, tiny bark beetles, circular or oblong cankers under bark, tiny entrance and exit holes

Affected Areas
Not yet found in NJ

For an annual update on the projects the New Jersey Forest Health Program is working on, visit https://www.fs.fed.us/foresthealth/protecting-forest/forest-health-monitoring/monitoring-forest-highlights.shtml and click on NJ.