Insect & Disease Glossary

Our Insect & Disease Glossary features information, tips, and tactics, for managing pests in New England. Pest management can be a challenging subject, especially considering the effect our diverse weather has on the phenology in the area. This results in dynamic insect and disease outbreaks and requires expert pest management knowledge in order to control, manage, and prevent pests. This glossary is a great source of educational information regarding insects and diseases on our trees, plants, and shrubs.


Hemlock Woolly Adelgid

Hemlock Woolly Adelgid (HWA) is threatening one of our most valuable native trees – the Eastern Hemlock. HWA is a tiny, aphid-like insect introduced to the United States from Asia. Since it was first discovered in Massachusetts in 1988, Hemlock Woolly Adelgid has slowly spread throughout the region, usually carried by birds or wind. In addition to being tiny, HWA is different than other insects as it lays dormant much of the growing season and is active throughout the winter, producing new egg masses as early as mid-Ferbruary. Treatments for HWA; however, need to be done in the Spring.

HWA is easily recognized by the presence of white cottony egg masses on young Hemlock twigs. Damage is caused when these eggs hatch and begin to feed by sucking the sap from the twigs, effectively killing them. Healthy trees infested with HWA may live for 5 to 10 years untreated, while trees stressed by poor growing environments and droughts may only last 3 years.

Evidence of the destruction caused by HWA can be seen at Arnold Arboretum’s Hemlock Hill in Boston. The insect was first discovered in the area in 1997, and since then, the entire population of roughly 1,900 Hemlocks has become infested. To date, over 500 Hemlocks at Arnold Arboretum have been lost due to Hemlock Woolly Adelgid.

Once HWA has been identified on your trees, it should be treated quickly, as this is an extremely dangerous pest. An effective, yet non-toxic form of treatment for HWA is the application of Horticultural Oil. It is recommended that you use preventative treatment programs to ensure HWA does not infest your trees, and an application of Horticultural Oil in the Spring and Fall can help prevent the spread of Hemlock Woolly Adelgid, and ensure the preservation of your beautiful Hemlocks.

Asian Longhorned Beetle

Asian Longhorned Beetle (ALB) is an invasive insect from Asia that is a serious threat to hardwood trees in the U.S., including maple, elm, willow, birch, horsechestnut, and poplar. The ALB is approximately 1” to 1.5” long, with antennae that can be as long as the body itself.

During its infant stage, the ALB bores into a tree’s heartwood and feeds on the tree’s nutrients. This tunneling causes severe damage and can easily kill a tree. Once the insects have tunneled into the tree, they will continue to feed throughout the winter and develop a hard casing before they chew their way back out during the summer. This will leave noticeable round holes in the tree, which are a sure sign that the tree is infested. Once they have exited the tree, the ALB will feed on the leaves and twigs before re-entering the tree for the winter.

Once the ALB is detected, quick action is necessary as they can multiply rapidly. Upon detection, you are urged to contact the U.S. Department of Agricultures’ (USDA) local Animal and Plant Health Inspection Service (APHIS) Director, who can be located at the following website:

Extensive multi-year insect management programs are available to prevent this invasive pest from nesting in your trees.

Cottony Scale

Cottony Scale insects are closely related to aphids and affect Holly, Euonymus, Yews, and a variety of other trees and shrubs. Cottony scale occurs when scale insects feed by tapping into the plant stem or leaf and withdrawing plant sap. Plants infested with scale will show signs of thinning, yellowing foliage, and even branch dieback. In severe cases, cottony scale can kill a plant or tree.

Plants that are exposed to severe drought or weather damage are at a high risk of scale insect infection, and Certified Arborists recommend treating plants with an intensive insect management program to prevent cottony scale infestation.

Lace Bugs

Lace Bugs are small, winged-insects that are common on New England’s most popular trees and shrubs, such as the rhododendron, azalea, Hawthorne, and many other broad leaf and deciduous trees. The Lace Bug gets its name because its entire body is covered in veins, thus resembling the appearance of lace. The adult Lace Bug only grows to about 3 to 6 mm, and has wings with a net-like pattern and scattered brown or black dots.

Damage caused by Lace Bugs begins to appear in yellow spots on the upper leaf surfaces of infected plants. This is caused by the Lace Bug feeding on the underside of the leaf, using its piercing and sucking mouths to damage the leaves. The yellow spots occur because the Lace Bugs kill the cells within the leaves. When the feeding damage becomes severe, the leaves will take on a gray blotched appearance or can turn completely brown.

Due to the breadth of trees and shrubs that Lace Bugs affect, it is common to categorize the varieties into two groups – those that attack deciduous trees and those that attack evergreens. The deciduous group includes the Hawthorn Lace Bug, Oak Lace Bug, Hackberry Lace Bug, and Sycamore Lace Bugs; while the evergreen group features the Rhododendron Lace Bug, Azalea Lace Bug, and the Andromeda Lace Bug. What is unusual about these Lace Bug species is that the life cycle varies greatly across varieties, some having only one generation per year, while others have three or more.

Treating Lace Bugs requires pest control applications to the foliage of infested trees. It is also recommended that you use preventative applications to protect against Lace Bugs on your trees.

Gypsy Moth

The Gypsy Moth was introduced to Massachusetts from Europe by Professor Leopold Trouvelot in 1869, who was hoping to start a silk production with the moths; however, a few caterpillars escaped and quickly spread throughout the North East. Gypsy Moths are most commonly found on oaks, but have been known to devastate a wide variety of trees, including, hemlock, pine, spruce, willow, birch, and poplar. Once the Gypsy Moth caterpillars infest a tree they can quickly defoliate it by consuming all the leaves. Though a tree may survive one year of defoliation, multiple years of repetitive defoliation will kill a tree.

Since Gypsy Moths have become so abundant throughout the North East, treating them has become difficult. Arborists recommend comprehensive insect management programs in order to reduce the pests and prevent spreading of Gypsy Moths.

Fall Web Worm

The Fall Web Worm (hyphantria cunea) is a pest that is found throughout New England, and is common on a variety of shade trees and shrubs.  The Fall Web Worm appears on our deciduous trees in the late summer and is very similar to the Eastern Tent Caterpillar, with the only difference being how the insect builds its nests. Fall Web Worm nests can be found at the end of branches, and consists of a white hair-like mass that houses up-to a thousand eggs.

Fall Web Worms can cause damage to your deciduous trees in both the larval and mature stages. When in larval form, Fall Web Worms consume the leaves within their nests. Once they mature, the web worms begin to consume leaves outside of the nests, and spread throughout your trees. Though the risk of defoliation is low, it is possible. Managing these pests early is necessary to ensure they do not damage your trees. Non-chemical and chemical pest management programs can prevent or reduce the Fall Web Worm from infesting your trees and shrubs.

Winter Moths

Winter moths are invasive pests, originating from Europe and Western Asia. These insects were first found in North America in the 1930s; however, their population in Massachusetts has recently exploded, causing home owners, property managers, and arborists tremendous stress, as Winter moths shredded and stripped the leaves off of all their trees. Winter moths will infest many different types of deciduous trees, including cherries, crabapples, dogwoods, maples, and oaks. Winter moth, and their larvae are most common in eastern New England, primarily Boston’s North and South Shores; however, they continue to spread throughout the entire North East and Canada. Areas in the pacific North West have seen substantial Winter moth infestation as well.

The larvae (caterpillars or worms) of the Winter moth hatch and feed ravenously on leaves beginning around mid-May. Winter moth larvae will feed on leaf clusters and inside buds during the day and inch their way to the outside of leaves at night. In June, the larvae will drop to the ground and bury themselves in the ground until the Fall. Between October and November, male adult Winter moths emerge from the soil as moths. The females, who have no wings, slowly climb up a tree’s trunk in order to lay their eggs in the bark crevices.

Treating Winter moths should be done in the Spring when foliar applications and microinjection can be used to prevent Winter moth infestation. There are various applications that can control the Winter moth population on your trees, including B.t. Kurstaki, Spinosad, and insecticidal soap; however, consulting with a Certified Arborist is recommended to ensure safety and effectiveness.

Eastern Tent Caterpillar

The Eastern Tent Caterpillar is a common pest found throughout the United States. These insects are often confused with the Fall Web Worm; however, Eastern Tent Caterpillars nest around the joints and groins of trees, rather than at the tips. Look for signs of Eastern Tent Caterpillars in the spring and early summer as they will begin to show up on your plants and trees, and build their white hair like nests around the joints of your trees.

Like many other caterpillars, the Eastern Tent variety is social, meaning that they can join together to develop huge colonies and cause severe defoliation to your trees. Managing these insects can be difficult. As soon as you see signs of Eastern Tent Caterpillars, or if you have had previous infestationyou should consider a comprehensive insect management program to help manage these pests.


Diplodia Tip Blight

Diplodia Tip Blight is most commonly found in Austrian and Red pines but can be present on White pines, evergreens, and spruce trees. This disease is usually found in mature trees that encounter stress, such as drought, damage, winter drying, or root restriction. Repeated seasons of stress from Diplodia Tip Blight can lead to the tree turning brown, entire branches dying, and the tree becoming deformed.

Curled needles, brown needles, or dead needles, on the tips of pine trees are indicators of Diplodia Tip Blight, and year-after-year infection without treatment will kill the tree. Look for brown-tipped needles early in the growing season to catch the disease early. Comprehensive disease management programs are the most effective means of treating Tip Blight.


Anthracnose is a general name for a disease caused by fungi on various types of trees and plants. Anthracnose can occur in many shade trees, including oak, maple, elm, and sycamore, and can be detected by a cup-like fruiting called acervuli. This disease is species-specific, which means that the fungi in one host tree cannot cause damage to a tree of another variety. Common symptoms of anthracnose include branch dieback, leaf blighting, and small lesions on leaves and fruit.

In our region, Anthracnose is most commonly found on Eastern hardwoods. Leaves on hardwoods with Anthracnose will appear as though they have a burnt area, usually brown or black in color, which is why the disease is often referred to as Leaf Blight. Anthracnose is spread by rain, wind, or animals and insects, and can make the tree more susceptible to additional diseases. It is best to utilize a disease prevention program in order to prevent Anthracnose.

Leaf Spot

Leaf Spot is a disease that affects trees and shrubs and is extremely common across New England. Leaf Spot can be caused by insects, pollutants, and bacteria, but is most commonly a pathogenic fungus that can be identified by brown or black spots, or blotches, that are left on leaves.  This fungus can continue to grow to a point where it kills the leaves and causes defoliation.

Deciduous trees, such as oak, ash, maple, and hickory, are common hosts of leaf spot, while coniferous trees are less impacted. Though the leaf spot doesn’t usually infect coniferous trees, if it does happen, these trees can be severely damaged. Watch for the tell-tale brown and black spots, or defoliation, in order to identify leaf spot. In order to prevent or control Leaf Spot, comprehensive disease management programs can be applied.

Powdery Mildew

Powdery Mildew is a general name for numerous fungus diseases on ornamental trees and shrubs. Most commonly infected plants include lilacs, rose varieties, and fruit trees, but Powdery Mildew can be apparent on many tree and shrub varieties. Like other fungal diseases, Powdery Mildew causes damage to leaf form and color and fruit quality. Nutrients are stripped from the plants, often causing severe damage to the vigor of the plant or tree.

True to its name, Powdery Mildew looks like a powdery white or gray coating found on the surfaces of leaves. Though it often starts out in small, discrete blotches, Powdery Mildew can expand quickly, covering entire leaves at times. In New England, this fungus normally becomes an issue later in the growing season, as temperature and humidity increase. Plants in extremely tight quarters will often become infected with Powdery Mildew as humidity in such spots can be abnormally high. Although it strives in hot and humid conditions, Powdery Mildew is capable of surviving harsh winters on infected plant parts and fallen leaves.

Treating and preventing Powdery Mildew requires applications of treatment to leaves and infected areas. Any fallen leaves that are infected should be gathered and destroyed as to not spread the disease further.

winter moth

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