Forest Pests - Insects and Diseases

Are you having trouble deciding if that insect or plant is friend or foe? Thankfully there are several resources available to help you identify the biota in your area.

Virginia Cooperative Extension has an online service, Ask an Expert. Questions submitted are answered by Cooperative Extension, University staff, and volunteers.

Fairfax County Master Gardeners hold Plant Clinics in various locations throughout the Fairfax County from May through September. They help the public with gardening questions, plant and insect identification, and soil tests.

Download the free iNaturalist app to your mobile device, available for both Android and iPhone. You will have to create a free profile to begin. You will be able to take photos of plants and insects and get suggestions on what species they may be.

Tree Identification tools will help you find the species of tree which will help you find information on how to properly care for it.

The exotic and invasive tree of heaven (Ailanthus alsima) is the preferred host of the invasive insect pest, spotted lanternfly (Lycorma delicatula). Fairfax County urban foresters want your help to locate and report observations of the invasive tree of heaven.

Become a first detector in the fight against spotted lanternfly! The Early Detection and Distribution Mapping System (EDDMapS) is used to report invasive species. Tree of heaven location reports can be made directly in the app. Download the brochure to learn in details.

Oak decline is a condition that affects oak trees and is characterized by a number of symptoms, including leaf yellowing, sprouts on the trunk and limbs, browning leaves, and thinning of the canopy. It can also cause the death of small twigs and larger branches, and over many years or decades, lead to tree death. The cause of the widespread decline of oak trees is believed to be the result of a combination of factors including tree age, environmental stress, pests and diseases, and improper care.

The easiest and most effective way of reducing the impact of insects and diseases that could harm your trees is by alleviating environmental stresses that impede your tree’s ability to defend itself against an attack. Trees that are properly maintained and growing under optimal conditions are also less likely to develop costly problems in the future as a result of environmental stresses. Tree owners can take simple steps that go a long way toward improving the vitality of their trees and ensure they get the most benefits from their trees in the long-term.

The asian longhorned beetle is one of the most serious and destructive tree pests to strike North America. Asian longhorned beetles to date have not been found in Fairfax County. Photo courtesy of USDA

Emerald ash borer (EAB) is a beetle that was accidentally introduced into North America from Asia. EAB infests all species of ash and is almost always fatal without treatment. Photo by: David Cappaert, Michigan State University

The fall cankerworm is a native defoliating insect found throughout much of North America. Severe infestations of cankerworms can cause widespread defoliation, tree stress and possible tree death. Major infestations and defoliation have occurred in Fairfax County. Photo by: Joseph Berger, Bugwood.org

In 1869, the spongy moth escaped from a Massachusetts lab and became established in North America. It continues to be a serious insect threat to trees and shrubs in the United States. There are several caterpillars common to Fairfax County which are often mistaken for spongy moth. Photo By: Joseph BergerUSDA Forest Service - Region 8 - Southern Archive, Bugwood.org

The hemlock woolly adelgid (Adelges tsugae), commonly referred to as HWA, is an aphid-like insect native to East Asia. It feeds on nutrient and water storage cells at the base of hemlock needles. This exotic, invasive insect was likely imported into the United States on Japanese hemlock nursery stock in the 1950s.

The spotted lanternfly is an invasive insect that is native to East Asia. Like many exotic insects, it has no known natural enemies in the United States to keep the population under control. This insect is a plant hopper and the nymphs and adults are excellent jumpers. Adults use their two pairs of colorful wings when they jump and glide.

Beech bark disease (BBD) is a devastating and fatal disease complex which affects American beech (Fagus grandifolia) as well as ornamental beech species (European beech, Fagus sylvestris and others). BBD was accidentally imported into Nova Scotia, Canada around 1890 on ornamental beech. Since then, it has been spreading slowly southward throughout the eastern United States. Humans also contribute to disease spread by transporting firewood.

Beech leaf disease (BLD) is a relatively new disease of native American beech (Fagus grandifolia) as well as the commonly planted European beech (Fagus sylvatica), and Asian beech (Engleriana subspecies). It is associated with a microscopic roundworm or nematode (Litylenchus crenatae mccannii) that feeds inside the leaves. Saplings can die in only a year or two while older trees may die over several years.

Sudden Oak Death (SOD) is caused by the mold pathogen Phytophthora ramorum. Fairfax County UFMD Forest Pest Branch is cooperating with the United States Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS) to watch for this disease in Fairfax County.

Thousand cankers disease (TCD) is caused by a fungal pathogen and bark beetle that is fatal to black walnut. Thousand cankers disease now threatens the health and survival of black walnut across its entire native range including here in Fairfax County. 

Invasive species can lead to the extinction of native plants and animals, reduce biodiversity, and permanently change habitats. Learn more and share with others what invasive species are, their damaging effects and the need to control them. Find out what we are doing in Fairfax County, what you can do to make a difference and how to recognize, prevent, control, and report them.