Maryland’s trees face constant threats from pests that can damage their health, property value, and local ecosystems. Here’s a quick summary of the most common pests and their impact:

• Emerald Ash Borer: Kills ash trees within 3 years. Look for metallic green beetles, S-shaped tunnels under bark, and crown dieback.
• Spongy Moth (Gypsy Moth): Defoliates oaks and other trees. Watch for egg masses, caterpillars with blue and red dots, and severe leaf loss in June.
• Bagworms: Attack evergreens like arborvitae and junipers. Identify by cone-like silk bags hanging from branches.
• Eastern Tent Caterpillars: Build silk tents in branch crotches of cherry and crabapple trees. Defoliation is common in spring.
• Spotted Lanternfly: Feeds on over 70 plant species, including red maple and grapevines. Look for sap oozing from bark and sooty mold buildup.
• Aphids: Infest both deciduous and evergreen trees, causing yellowing leaves, sticky honeydew, and sooty mold.
• Scale Insects: Small pests that weaken trees by feeding on sap. Look for yellowing leaves, branch dieback, and sticky honeydew.
• Japanese Beetles: Skeletonize leaves of maples, crabapples, and cherries. Active during summer.
• Two-Lined Chestnut Borer: Targets stressed oaks, causing branch dieback and D-shaped exit holes.
• Spider Mites: Thrive in hot, dry conditions. Cause yellowing leaves, fine webbing, and leaf drop.

Key Takeaways:

• Early detection is critical to save trees and avoid costly damage.
• Healthy trees are more resistant to pests – regular watering, pruning, and soil care are essential.
• Professional monitoring and targeted treatments can effectively manage severe infestations.

By staying vigilant and addressing issues promptly, you can protect your trees and maintain Maryland’s natural beauty.

Maryland Forest Health Report: Pests and Diseases- Heather Harmon Disque- Episode 1

Maryland’s Tree Pest Problems

Maryland’s mix of diverse tree species and a changing climate creates a perfect storm for pest infestations. Rising temperatures and shifting weather patterns have reshaped how tree pests survive and thrive year-round.

The state’s average annual temperature is now nearly 4°F higher than it was between 1895 and 1915 ^[5]. From 1970 to 2016, Maryland saw an increase of 3.7 days per year with temperatures over 95°F. Nights above 75°F, which were rare in 1950, now occur about seven times annually ^[5]. Winters have also warmed significantly, with about 30 fewer freezing days compared to 1910 ^[5].

These milder winters allow more pests to survive. The University of Maryland Extension describes the situation:

"Many more insect pests are also surviving the winter in Maryland or nearby states, increasing their abundance in spring. This means that in general you can expect insect pests to appear earlier in the summer and be more abundant." ^[5]

Maryland’s tree species face specific pest threats. Ash trees, for example, are highly vulnerable to the Emerald Ash Borer, a pest capable of killing a tree within three years of infestation. Oak trees, which are widespread across the state, frequently fall victim to Spongy Moths (formerly known as Gypsy Moths), which can strip their leaves and weaken the trees significantly.

In urban and suburban areas, the variety of tree species makes pest control even more challenging. Eastern Tent Caterpillars often target Willows, Poplars, Maples, Cherry, and Crabapple trees – favorites in residential landscaping. Meanwhile, evergreens like Boxwoods, Cypress, and Junipers face attacks from Spider Mites. Other pests, such as Aphids, frequently infest Spruce, Crape Myrtles, Ash, Fir, and Cedar trees.

Adding to the problem, Maryland now receives about 4.5 inches more rainfall annually than it did during the early 20th century ^[5]. While trees need water, excessive rainfall combined with severe storms can weaken them. Stressed trees lose their natural defenses, making them prime targets for pests to invade and multiply.

Earlier springs also upset the balance between trees and their natural pest predators. This timing mismatch often leaves trees defenseless during critical growth periods, giving pests a head start. Unfortunately, most tree issues aren’t noticed until damage is severe, making treatment more complicated and costly ^[6].

Healthy trees are naturally better equipped to resist pests ^[7], but even the strongest trees face mounting challenges in Maryland’s changing environment. With pests thriving under favorable conditions, property owners must stay vigilant. Effective pest management has never been more important.

Next, we’ll take a closer look at some of Maryland’s most destructive pests, starting with the Emerald Ash Borer.

1. Emerald Ash Borer

The Emerald Ash Borer (EAB) is a highly destructive beetle that has wreaked havoc on Maryland’s ash trees. This invasive pest has already wiped out most ash trees west of the Chesapeake Bay and continues to spread through the state’s wetland forests.

Identification Features

Adult Emerald Ash Borers are small, metallic green beetles about the size of a grain of rice – roughly 1/2 inch long and 1/8 inch wide ^[8][9]. Their bright, shiny appearance makes them stand out, though they can sometimes be confused with other metallic green insects ^[9].

Their larvae, on the other hand, are white, flattened grubs that grow up to 1.5 inches long ^[10]. These larvae feed beneath the bark, creating distinct S-shaped tunnels known as larval galleries ^[14][15]. When adults emerge, they leave behind D-shaped exit holes about 1/8 inch wide, which are noticeably different from the round or oval holes left by native borers ^[9][15]. These features make it easier to identify and confirm an EAB infestation.

Host Trees

EAB primarily infests true ash species (Fraxinus spp.) but has also been found in white fringe trees (Chionanthus virginicus) ^[11]. Across U.S. cities, ash trees make up more than 20% of urban tree populations ^[13]. In Maryland, Pocomoke River State Park stands out as one of the last major refuges of ash wetland forests ^[12].

Damage Signs

The damage caused by EAB is severe and often fatal for infested trees. Larvae feeding beneath the bark disrupt the tree’s ability to transport water and nutrients, leaving behind S-shaped tunnels. Signs of infestation include crown dieback, epicormic sprouting (new shoots on the trunk or branches), bark splits, and increased woodpecker activity. Affected trees also show yellowing leaves and typically die within 8–10 years of infestation ^[8][14][15]. These devastating effects highlight the critical need for early detection to protect Maryland’s urban and wetland forests.

2. Gypsy Moth

The Gypsy Moth, now officially referred to as the Spongy Moth ^[20], underwent a name change to address concerns about its previous designation. This pest is infamous for being one of Maryland’s most destructive invaders. Since 1980, it has defoliated nearly one million forested acres annually across the U.S. ^[21]. In Maryland, the damage has averaged over 40,000 acres each year, with one particularly severe outbreak stripping 68,000 acres in a single season ^[19][23].

Identification Features

Spongy moths are easily recognized at different stages of their life cycle:

• Egg Masses: These clusters are oval-shaped, about 1.5 inches long and 0.75 inches wide, and covered with a yellowish or buff-colored, hair-like material. Each mass can hold up to 1,000 eggs and is often found on tree trunks, stones, outdoor furniture, walls, and logs ^[16].
• Caterpillars: Young larvae are black and hairy, but as they grow, they develop a mottled yellow-to-gray pattern with bristle-like hairs. Their most distinctive feature is the pattern of five pairs of blue dots followed by six pairs of red dots on their backs, which helps differentiate them from native species ^[16].
• Adult Moths: Male moths are brown with darker wing patterns, a 1.5-inch wingspan, and feathery antennae. They fly during the day in a zigzag pattern ^[16][17][18]. Females, on the other hand, are nearly white, slightly larger with a 2-inch wingspan, and flightless. Their wings have dark, saw-toothed patterns ^[16][17].

These features make it easier to identify the pest and understand its impact on a wide range of host plants.

Host Trees

Spongy moth caterpillars have a strong preference for oak trees but are far from selective. They also attack sweetgum, linden, willow, birch, apple, alder, boxelder, and blue spruce, among others. In fact, these caterpillars can defoliate more than 300 types of trees and shrubs ^[16][22].

Bob Tichenor from the Maryland Department of Agriculture highlighted the broader consequences for Maryland’s forests:

"Gypsy moths strip the leaves in June. The trees re-foliate in July, when it’s hot and dry. It’s a real disadvantage to the trees. This year, they re-foliate during one of the worst droughts in years. It sets them up for other tree diseases and boring insects, and they can’t fight them off as well." ^[23]

Damage Signs

The most obvious sign of a spongy moth infestation is severe defoliation. In heavily infested areas, forests can appear barren in the middle of summer, resembling a winter landscape. Unlike native caterpillars, which typically cause localized damage, spongy moths can strip entire forests of their foliage. Trees that lose more than 50% of their leaves for two consecutive years become significantly weakened. Prolonged defoliation can eventually kill mature trees by depleting their energy reserves ^{[1][16][18][19][22]}.

The USDA APHIS emphasizes the importance of early intervention:

"Early detection is critical to limit the spongy moth’s spread to new areas. If left unchecked, this pest can strip leaves and even kill trees, if severe defoliation persists for multiple seasons." ^[16]

Homeowners in Maryland are encouraged to check their properties for egg masses on tree trunks, fences, walls, outdoor furniture, and other surfaces. If egg masses or signs of defoliation are identified, they should be reported to Maryland’s spongy moth program at 410‑841‑5922. To destroy egg masses, scrape them into a zip-top plastic bag filled with water and detergent ^[1][16]. Recognizing these damage signs is crucial for managing the pest and understanding its seasonal cycle.

Seasonal Activity

Spongy moth egg masses overwinter on tree bark and other surfaces, hatching in the spring as temperatures rise. The caterpillars feed actively through late spring and early summer, with peak defoliation occurring in June ^[23]. After pupating, adult moths emerge in mid to late summer. Males fly during the day in a zigzag pattern, searching for flightless females to mate with. Females lay their egg masses in late summer and fall, completing the cycle for the next generation ^[17][18].

3. Bagworms

Bagworms are the larval stage of moths and are known for creating one of the most recognizable pest signs on Maryland trees. These caterpillars construct protective bags using silk and bits of plant material, giving them the appearance of pinecones hanging from branches ^[25][27]. Board Certified Master Arborist Wayne White once observed a single bagworm sack on a spruce tree in Plainfield, IL, containing between 300 and 1,000 eggs – a staggering potential for infestation ^[26].

Identification Features

The hallmark of bagworms is their unique bags, which can grow up to two inches long ^[26]. These bags, crafted from silk and plant debris, are designed to blend in with the tree or shrub they inhabit ^[28]. On evergreen trees, the bags often take on a cone-like shape, making them easy to mistake for part of the tree’s natural foliage ^[28].

Bagworms are mobile feeders, carrying their bags with them as they move from branch to branch ^[24]. As they feed, the bags grow larger throughout the summer. If you see casings that move when touched or notice areas of the plant showing dieback, these are signs of active bagworms ^[25].

Host Trees

Bagworms are a serious threat to a wide range of ornamental trees and shrubs in Maryland, with over 128 plant species at risk ^[29]. Conifers, including arborvitae, cedar, juniper, and pine, are especially vulnerable. These pests are notorious for targeting the needles of evergreens like arborvitaes, junipers, Leyland cypresses, and cedars ^[24][30].

While deciduous trees such as sycamore, maple, locust, boxelder, and linden can also be affected, they typically recover more easily from damage ^[24]. Regardless of the host, once bagworms establish themselves, the plants often show clear signs of distress.

Damage Signs

Catching bagworm infestations early is key to preventing widespread damage ^[31]. Early in the season, these pests and their small bags can be hard to spot ^[24]. However, as the infestation progresses, trees and shrubs may start to look sickly, with pale or browning foliage that eventually falls off – even with proper watering and fertilization ^[33].

Young bagworms create tiny holes in leaves as they feed. By the time they grow to about an inch long, they can strip entire leaves, leaving only the veins behind ^[31]. Severe infestations can kill plants within weeks ^[31].

Signs of damage include defoliation, brown patches, twig dieback, and a sudden decline in the appearance of evergreens. Branches and boughs may turn brown or die off, leaving the plant looking sparse and unhealthy ^{[24][28][33][34]}. Each female bagworm can lay up to 1,000 eggs, leading to rapid population growth if left unchecked ^[32].

Seasonal Activity

Bagworms follow a predictable seasonal cycle, which can help guide detection and treatment efforts. The larvae hatch in late spring and immediately begin building their protective bags. They feed actively during the summer months, with their bags growing larger as they mature ^[24]. The peak activity period typically falls between mid-June and August, making this the best time to inspect host plants for small bagworms on leaves or needles ^[28][32].

4. Eastern Tent Caterpillars

Eastern tent caterpillars are one of Maryland’s most familiar tree pests, known for their ability to defoliate ornamental and fruit trees.

Identification Features

The easiest way to spot eastern tent caterpillars is by their silk tents, which they weave in the crotches where branches meet the trunk^[35].

Fully grown caterpillars are 2–2½ inches long^[35][37]. They have a bold white stripe running down the center of their back, bordered by yellow stripes on either side^[35]. Their bodies are a mix of blue, yellow, and black, covered with fine hairs for protection^[35]. Younger caterpillars are darker, with two thin yellow lines on their backs, developing brighter colors as they grow and molt^[35].

Females lay eggs in distinctive black, shiny masses that wrap around small twigs. Each mass can contain 150–350 eggs^[35].

It’s important to differentiate eastern tent caterpillars from other similar pests. For instance, forest tent caterpillars have white dots instead of a solid white stripe and don’t build tents^[35]. Similarly, fall webworm nests are found at branch tips and enclose leaves, unlike the silk shelters of eastern tent caterpillars, which are built in branch crotches and don’t cover foliage^[36].

Once you recognize these traits, inspect common host trees for signs of infestation.

Host Trees

Eastern tent caterpillars are especially drawn to trees in the Rosaceae family, such as cherry, crabapple, and apple trees^[38]. In Maryland, black cherry trees are their primary target^[39].

They also attack a wide range of other trees, including fruit trees, hardwoods like ash, maple, and oak, and ornamentals such as wild cherries, ornamental cherries, plums, and crabapples. Other trees like pyracantha, willows, and poplars are also at risk^[40][3].

When caterpillars strip their host tree of leaves, they often move on to nearby woody plants, spreading the infestation^[38]. These outbreaks tend to occur in cycles, roughly every 10 years, making them a recurring issue for Maryland tree owners^[38].

Damage Signs

Eastern tent caterpillars damage trees by eating their leaves^[42]. Early signs of infestation include silky nests in branch crotches and thin webbing on affected trees. Once established, the damage can quickly spread to nearby shrubs and trees^[41][42].

These pests are particularly harmful because they feed just as leaf buds are opening in spring, a vulnerable time for trees^[41].

The University of Maryland Extension explains the primary impact:

Impacts from Eastern tent caterpillars are primarily aesthetic because some people consider the tents unsightly. They do not typically substantially damage or kill trees unless the trees are small and repeatedly defoliated^[38].

Healthy, mature trees can usually recover even after complete defoliation, as noted by Michael J. Skvarla of Penn State Extension:

Healthy deciduous trees can withstand total defoliation multiple years in a row without long-term detrimental effects, so it is not recommended to attempt to control caterpillars in natural forest settings^[35].

However, young or stressed trees are more vulnerable. Repeated defoliation can weaken them significantly, and in severe cases, small trees may die from the stress^[38][42]. The situation becomes more serious when trees face repeated defoliation over several years.

Seasonal Activity

Tracking their seasonal cycle helps in managing infestations. Eastern tent caterpillars follow a predictable pattern, making it easier to time interventions. Eggs hatch in early spring as temperatures rise and tree buds swell, providing the fresh leaves that young caterpillars prefer.

Spring is the active feeding period. After hatching, the caterpillars construct their silk tents and begin feeding on nearby leaves, growing rapidly as they molt several times.

By late spring or early summer, the feeding phase ends. Mature caterpillars leave their host trees to pupate, eventually emerging as moths in mid to late summer. These adults mate and lay egg masses on tree branches, where they remain dormant through winter, ready to hatch the following year.

Understanding this cycle allows homeowners to act at the right time to protect young fruit or ornamental trees that are more susceptible to lasting damage.

5. Spotted Lanternfly

The spotted lanternfly is a troublesome invasive pest that poses a serious threat to over 70 plant species, including Maryland’s trees, vineyards, and forests.

Identification Features

Spotted lanternflies are easy to recognize at different stages of their life cycle.

• Egg masses: These are most visible during fall, winter, and spring. Fresh egg masses look like wet gray putty but dry into a dull brown, cracked mud-like texture on tree bark. Older ones turn brown and scaly, measuring about 1 inch long. Each mass contains 30–50 eggs and often appears as yellowish-brown waxy deposits on smooth surfaces^{[43][45][46][48]}.
• Nymphs: In their early stage (April–July), nymphs are black with white spots. By mid-summer (July–September), they turn bright red with black and white markings^[44][45].
• Adults: Measuring about 1 inch by 0.5 inch, adults have a yellow abdomen with black bars, gray forewings with black spots, and striking scarlet hind wings with black and white patterns. Their unique appearance makes them hard to mistake for any other insect^[43][44][47].

The Canadian Food Inspection Agency highlights their unmistakable look:

Because of its distinctive appearance, this insect is not easily confused with any other insect known to occur in Canada^[47].

Host Trees

While the spotted lanternfly can feed on a wide variety of plants, it shows strong preferences for certain species. Its favorite is the Tree-of-Heaven, but it can survive without it^[49].

A 2020 study at a shopping center revealed how selective they can be. Even though red maples made up 31% of the trees, they hosted over 94% of the spotted lanternfly population^[49].

• Preferred hosts: Tree-of-Heaven, Red Maple, Black Walnut, River Birch, Willow, Sumac, and Grapevines are among the most favored trees and plants.
• Nymphs: Early-stage nymphs feed on a broader range of plants, including herbaceous species and young growth, before moving to other hosts^[49].
• Adults: Mature lanternflies focus on the woody stems of trees and vines, causing significant damage to established landscapes^[49].

Interestingly, conifers are less likely to suffer infestations, as spotted lanternflies rarely target them^[49].

Damage Signs

Spotted lanternflies harm trees by piercing the bark and sucking out sap, which weakens the plants and makes them vulnerable to disease^[45].

• Primary damage: Look for sap oozing from small wounds on tree trunks, often leaving wet, fermented-smelling areas. Dark streaks of sap may run down the bark where the insects have fed^[44][45].
• Secondary damage: The insects produce a sticky substance called honeydew, which builds up at the base of trees. This attracts bees, wasps, and other insects and encourages the growth of sooty mold – a black coating that covers leaves and bark, blocking sunlight and reducing photosynthesis^{[43][44][45][51]}.
• Advanced damage: Over time, trees may show signs of leaf wilting, branch dieback, and even death due to repeated feeding^[44].

The agricultural consequences can be severe. For example, in 2017, a Pennsylvania vineyard reported a 90% loss in grape yield, with the remaining grapes having poor sugar content due to lanternfly feeding. By 2018, the most affected vines couldn’t survive the winter. During this period, pesticide applications in some vineyards skyrocketed from an average of 4.2 treatments in 2016 to 14.0 in 2018, leading to a 408% increase in costs^[50].

Seasonal Activity

Understanding the seasonal behavior of spotted lanternflies can help in planning control measures. Eggs hatch in spring, and nymphs (black, then red) feed until September. Adults emerge after that and remain active until the first hard frost. They often gather in large groups on tree trunks and stems, especially at dusk and nighttime, when they mate and lay eggs for the next generation^[43].

During winter dormancy, egg masses stay attached to trees and other surfaces, waiting for warmer spring temperatures to hatch.

The New Jersey Department of Agriculture stresses the pest’s widespread impact:

Spotted lanternfly is a serious invasive pest with a healthy appetite for our plants and it can be a significant nuisance, affecting the quality of life and enjoyment of the outdoors^[52].

These seasonal patterns are crucial for developing effective management strategies, which will be detailed in the next section.

6. Aphids

Aphids are tiny but highly destructive pests that can infest both deciduous and evergreen trees across Maryland. Despite their small size, their ability to reproduce rapidly makes them a significant threat to trees.

Identification Features

Aphids are soft-bodied insects, measuring less than 1/8 inch (3 mm) in length ^[54]. Their bodies are pear-shaped or oval and come in a variety of colors, including green, yellow, brown, black, and even pink, depending on their species and life stage ^[54]. Here are some key features to help identify them:

• Long, slender antennae
• Distinct cornicles (tube-like structures) at the rear of their abdomen
• Soft, slightly translucent bodies
• Thin, elongated legs that allow them to move easily across plant surfaces
• Piercing-sucking mouthparts used to feed on plant sap ^[54]

Adult aphids typically range from 1 to 3 millimeters in size, while their nymphs are even smaller. Their reproduction is astonishingly fast – just one aphid can give birth to 40–85 offspring in a single month ^[53].

Host Trees

Certain tree species in Maryland are more prone to aphid infestations. Both evergreen and deciduous trees can be affected, with some species facing specialized aphid attacks.

Evergreens like spruce, fir, cedar, and crape myrtles are frequent targets. White pines, for instance, are often infested by the white pine aphid (Cinara strobi), while other aphid species, such as Cinara, Eulachnus, Essigella, and Schizolachnus, attack various types of pines ^[56]. Juniper and fir trees are also common hosts.

Deciduous trees are not spared either. Woolly apple aphids often infest crabapple trees but can also be found on alder, elm, hawthorn, mountain ash, serviceberry, and Pyracantha ^[57]. Beech blight aphids, on the other hand, are known to specifically target American Beech trees, feeding on their sap ^[58]. In Maryland’s apple orchards, spirea aphids have become more prevalent than apple aphids, though telling the two apart in the field is nearly impossible ^[55].

Damage Signs

Aphid infestations can cause several noticeable issues, including:

• Curling and yellowing of leaves
• Stunted growth in new shoots
• Sticky honeydew residue on leaves and nearby surfaces
• Black sooty mold forming on foliage
• Increased ant activity around affected areas ^{[56] [59] [60] [61]}

One of the most telltale signs of an aphid problem is the presence of honeydew, a sugary substance excreted by the pests. This sticky residue not only makes leaves tacky but also attracts ants and encourages the growth of sooty mold, which appears as black patches on the leaves ^{[56] [60] [61]}.

Seasonal Activity

Aphids tend to gather in dense groups, often on the undersides of leaves or around new growth ^[60]. Regularly inspecting new shoots, flower buds, stems, and leaf undersides is crucial for detecting infestations early ^[53]. Early intervention is essential to controlling their population and preventing extensive damage. Keep a close eye on early growth and address any signs of aphids promptly to limit their spread.

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7. Scale Insects

Scale insects are some of the sneakiest tree pests in Maryland, often staying under the radar until they’ve already caused serious harm. Like with other pests in the area, catching them early is the best way to manage their impact. These tiny pests are experts at blending in, making them tricky to spot and even harder to control.

How to Identify Scale Insects

Scale insects are small, soft-bodied creatures that shield themselves with waxy coverings, helping them hide on tree bark and branches ^[62]. These coverings can be brown, gray, or white, while the insects themselves often have rosy-red or purplish tones ^[62].

The shapes of their protective covers can give clues about the species. They might be round, rice-shaped, or oystershell-shaped, and they’re typically less than one-third of an inch long (8-9 millimeters) ^[62].

Scale insects fall into two main types:

• Soft scales: These develop a gum-like wax coating that sticks to their bodies.
• Armored scales: These produce a separate, shell-like cover. Mature females in this group become stationary, appearing as small bumps on tree surfaces ^[62].

Warren T. Johnson, a researcher from Cornell University, describes female scale insects as:

"integumental sacs that function as reproductive factories" ^[63]

This emphasizes their primary role in reproduction once they mature. Now, let’s look at which trees are most at risk.

Trees at Risk

Scale insects aren’t picky when it comes to their hosts. They target both hardwoods and conifers, making nearly any tree in Maryland a potential victim ^[4]. Stressed or weakened trees – especially those dealing with drought or poor soil conditions – are particularly vulnerable ^[66]. If left unchecked, heavy infestations can kill trees, underscoring the importance of early detection ^[65].

Signs of Damage

The damage caused by scale insects is often easy to spot if you know what to look for. Key warning signs include yellowing leaves, stunted growth, and branch dieback ^[62]. Different types of scale insects cause specific patterns of damage based on their feeding habits.

• Soft scales: These pests feed on sap in the phloem and leave behind a sticky substance called honeydew. This honeydew attracts ants and encourages sooty mold growth, a black, powdery mold that coats leaves and branches, further harming the tree ^[62].
• Armored scales: Unlike soft scales, these feed directly on individual plant cells and don’t produce honeydew ^[62].

Severe infestations can lead to premature leaf drop, poor foliage production, and weakened trees that are more susceptible to infections and winter damage ^[68]. For example, pine tortoise scale infestations can cause yellowing needles and branch dieback, and prolonged infestations can kill smaller plants, especially when combined with environmental stress ^[68].

When Are They Active?

Understanding the seasonal habits of scale insects is essential for managing them effectively. These pests are active for much of the growing season, with adult scales being the most noticeable stage. Depending on the species, adults may appear white, gray, or brown, and their shapes can range from round to pear-shaped or oystershell-like ^[67].

The crawler stage is the most vulnerable period for scale insects, making it the best time to apply treatments. During this phase, young scales move around the tree before settling in their feeding spots.

To catch infestations early, regularly inspect your trees – especially stressed or declining ones. Pay close attention to branches, twigs, and the undersides of leaves, as these are common spots where scale insects set up colonies. Mature scales, being stationary, are easy to miss until their numbers grow large enough to cause visible damage.

8. Japanese Beetles

Japanese beetles are one of the most recognizable pests in Maryland, known for their metallic appearance and aggressive feeding habits. These insects have become a major headache for homeowners and landscapers across the state, causing widespread damage to a variety of trees and plants during their active season. Let’s break down how to identify these beetles, their favorite targets, the damage they cause, and when they’re most active.

Identification Features

Adult Japanese beetles are small, measuring about 1/3 to 1/2 inch long, with a metallic green head and thorax, paired with coppery-brown wing covers ^[72][73]. A distinctive feature is the six pairs of white tufts of hair along their abdomen, which sets them apart from similar species ^[71][72]. Males are generally a bit smaller than females ^[69].

Their larvae, or grubs, are creamy white, C-shaped, and have tan-colored heads. Fully grown grubs can reach about 1 inch in length ^[70][71][75]. However, identifying Japanese beetle grubs can be tricky since they closely resemble other white grubs. Proper identification often requires examining the pattern of spines and hairs on the underside of their abdominal tip ^[75].

Host Trees

Japanese beetles are not picky eaters – they feed on over 275 plant species. However, they have a particular fondness for trees in the rose family ^[76]. In Maryland, some of their favorite targets include maple trees, ornamental apple and stone fruit trees, and elm trees ^[77]. Commonly attacked species also include crape myrtle, birch, littleleaf linden, crabapple, purple leaf plum, Japanese maple, Norway maple, weeping cherry, and ornamental cherry ^[78].

The good news? Some trees naturally resist Japanese beetle damage. Evergreen conifers like pine, fir, spruce, and arborvitae are typically avoided by these pests ^[78]. Other less-preferred trees include red maple, white oak, red oak, redbud, and rhododendron ^[78]. If you’re planning your landscaping, incorporating these less-attractive species can help reduce beetle-related problems ^[76].

Damage Signs

Japanese beetle damage is easy to spot once you know what to look for. The most obvious sign is skeletonized leaves, where beetles eat the soft tissue between the veins, leaving behind a lace-like pattern ^[74][79]. The USDA describes their feeding behavior as follows:

Adults leave behind skeletonized leaves and large, irregular holes in leaves. ^[81]

Beetles typically feed on the upper surfaces of leaves, avoiding the tougher vein structures as they chew through the softer parts ^[80]. In severe infestations, trees can take on a scorched, brown appearance due to extensive defoliation and browning ^[74][80]. This heavy feeding can weaken the tree, leading to premature leaf drop ^[80][82].

But it doesn’t stop there. Adult beetles also feed on flowers and fruits, further impacting the plant’s health and appearance. This comprehensive feeding can disrupt multiple aspects of a tree’s vitality and aesthetic appeal ^[77].

Seasonal Activity

Japanese beetles are most active during the summer months, when adults emerge and begin their feeding frenzy ^[73]. Understanding their seasonal patterns can help homeowners and landscapers plan effective interventions to protect their trees and plants.

9. Two-Lined Chestnut Borer

In Maryland, the Two-Lined Chestnut Borer (TLCB) plays a major role in the decline of oak trees. Oaks make up roughly 28% of the state’s total growing stock, so understanding this pest is crucial for property owners looking to protect their trees ^[85][87].

Identification Features

The adult Two-Lined Chestnut Borer is a small beetle, measuring between ¼ and ½ inch in length. It has a long, cylindrical body that’s black with two golden stripes running along its wing covers, or elytra ^[83]. The larvae are white, elongated, and flattened, with a noticeably wider thoracic segment just behind their head ^[83]. One telltale sign of their presence is the "D"-shaped exit holes they leave in the bark as they emerge as adults ^[83][84].

Host Trees

TLCB typically targets weakened oak trees, acting as a secondary pest by exploiting trees already stressed by environmental factors ^[85]. Red, black, and scarlet oaks are particularly at risk, but other species – such as white oak, chestnut oak, northern red oak, and live oak – can also be affected ^[85][86]. Conditions like defoliation from gypsy moths, drought, construction damage, forest fires, or pollution weaken these trees, making them vulnerable. Once infested, the larvae feed on the inner bark, creating winding galleries beneath the surface ^[85].

Damage Signs

The first signs of a TLCB infestation often appear by mid-July. Look for sparse, red-brown foliage and branch dieback that starts at the top of the tree and works its way downward ^[88][89][90]. A common visual pattern is "dead, red, and green", where some branches remain green while others turn red-brown ^[90]. D-shaped exit holes in the bark and larval galleries filled with pale frass beneath the bark are definitive indicators ^[88][89][90]. Other symptoms include wilting or yellowing leaves ^[92] and dead leaves clinging to branches for months ^[91]. Infested trees typically decline and die over several years ^[88].

Seasonal Activity

By mid-July, TLCB damage becomes most noticeable. To confirm an infestation, peel back bark from branches to check for feeding galleries and larvae ^[88]. For accurate identification, it’s best to consult a tree-care expert who can send samples to a diagnostic lab ^[88].

10. Spider Mites

Spider mites are a persistent problem for Maryland’s trees. These tiny arachnids thrive in hot, dry conditions and can quickly overrun trees already under stress ^[94].

Identification Features

Spider mites are incredibly small, measuring less than 1 mm (or about 1/20 of an inch). To spot them, you’ll need a magnifying glass; females are slightly larger than males ^[93][97]. As Tiffany Selvey explains:

Spider mites are so small that you need a magnifying glass to see them clearly ^[93].

Their color varies depending on the species and life stage, ranging from red, green, yellow, to brown. Unlike insects, spider mites have eight legs. To confirm their presence, try shaking a tree branch over a sheet of white paper. You’ll notice tiny moving specks, which can also be observed by closely inspecting leaves with a magnifying glass.

These traits make early identification possible, which is critical to preventing extensive damage.

Host Trees

Spider mites are highly versatile pests, attacking over 180 plant species and posing a major threat to Maryland’s tree diversity ^[93]. Specific species of spider mites tend to target particular types of trees:

• Spruce spider mites: Primarily affect conifers like spruce, hemlock, arborvitae, fir, juniper, and occasionally pine. Dwarf Alberta spruce is particularly vulnerable ^[98][99].
• Southern red mites: Infest broad-leaved evergreens such as hollies, boxwood, azalea, rhododendron, camellia, and laurel ^[98].
• Oak spider mites: Focus on oak species, especially pin and willow oaks, but can also damage birch, beech, elm, and hickory trees ^[98].
• Boxwood spider mites: Common boxwood is highly susceptible, while Japanese or littleleaf boxwood is rarely affected ^[64].

This wide range of host trees underscores the significant threat spider mites pose to the region’s greenery.

Damage Signs

Spider mite infestations leave telltale signs on their host plants. Leaves develop tiny white or yellow spots, lose their vibrant color, and may turn pale or bronze. Fine webbing often appears on new growth and the undersides of leaves ^[96][97]. Certified Arborist Sophia Huang stresses:

Detecting spider mites early is crucial for preventing severe damage to plants ^[97].

Infested leaves may also feel dusty or gritty due to a buildup of fecal matter, shed exoskeletons, and dead mites ^[96]. In severe cases, leaves and needles can scorch and drop prematurely, leaving trees with a gray or bronze appearance. Drought-stressed plants are especially prone to extensive damage from these pests ^[96].

Seasonal Activity

Spider mites are most active during Maryland’s hot, dry summers, thriving in temperatures around 80°F and humidity levels below 50% ^[96]. Under these conditions, a single female can lay dozens of eggs in just a few weeks, and species like the two-spotted spider mite can complete a generation in as little as five days ^[95][101].

To catch infestations early, monitor trees regularly during the summer. Inspect stems and the undersides of leaves for signs of mites or webbing. Shaking branches over a white card or tray can help dislodge mites, making them easier to spot ^[100][101]. Early detection and swift action are essential to minimize damage and protect Maryland’s trees.

Pest Management Methods

Managing pests effectively means taking a proactive stance by combining prevention, regular monitoring, and precise treatments.

Prevention Through Smart Tree Selection

One of the easiest ways to reduce pest problems is by choosing tree species that thrive in Maryland’s climate. Native trees like red oak, tulip poplar, and eastern redbud have natural defenses against local pests. When planting new trees, it’s smart to prioritize these species and steer clear of varieties that are highly vulnerable – like ash trees – especially in areas where pests such as the emerald ash borer are already present.

Regular Monitoring and Early Detection

Keeping a close eye on your landscape is key. Inspect trees every 6–8 weeks from late spring through summer for signs like yellowing leaves, cracked bark, or drooping branches. Professional monitoring programs in Southern Maryland often focus on spotting pests such as mites, bagworms, and lace bugs, along with diseases ^[102]. Pay extra attention to changes in tree structure, like bending or drooping branches, and check the undersides of leaves for hidden issues.

Cultural Practices for Tree Health

Healthy trees are less likely to fall victim to pests. Simple steps like pruning dead or infected branches with sterilized tools can prevent the spread of disease. Deep watering promotes strong root systems, making trees more resilient, while mulching helps retain soil moisture and keeps root temperatures stable.

Targeted Treatment Approaches

When pest problems arise, start with treatments that have minimal impact on beneficial insects. Horticultural oils and insecticidal soaps are good options for smaller infestations. For specific pests, here are some targeted actions you can take:

• Scrape spongy moth egg masses into a bag filled with water and detergent during the fall ^[1].
• Tear apart tent caterpillar nests to make the larvae accessible to birds ^[1].

If infestations become severe or keep recurring, it’s time to call in professional help.

Professional Tree Care Services

Preventive care and early detection are just the beginning. Pro Landscapes MD offers a range of tree health services across central Maryland, using an Integrated Pest Management (IPM) approach. This method focuses on overall tree health with practices like proper pruning, soil testing, and tailored fertilization programs. For example, deep root fertilization delivers nutrients directly to where they’re needed most. Regular assessments by professionals can identify problems early, ensuring treatments are timely and effective.

Soil Improvement and Environmental Management

Healthy soil is the foundation of strong, pest-resistant trees. Soil amendments can make a big difference – improving drainage in heavy clay soils or adding organic matter to sandy soils. Proper grading and drainage solutions also help prevent waterlogged conditions that can stress trees and make them more vulnerable to pests. Together, these practices bolster tree defenses and promote long-term health.

Conclusion

Protecting Maryland’s trees requires quick action and vigilant care. Tree pests don’t just threaten the health of individual trees – they can also harm property values and disrupt the delicate balance of the local ecosystem ^[2]. Alarmingly, up to 100 U.S. tree species could face extinction in the coming decades, with diseases like Beech Leaf Disease killing trees in as little as two to seven years ^[103].

Taking proactive steps is critical. Early detection of pests can prevent costly damage, defoliation, and hazards that negatively impact air quality and property values ^[2]. While healthy trees can often withstand 20–30% leaf defoliation without lasting harm ^[6], addressing issues before they escalate is key.

There’s also a financial incentive: properties with pest-resistant landscapes can see home values rise by 3% to 15% ^[106]. On a larger scale, efforts to combat invasive species could save billions in potential damage costs each year ^[107].

"Our society needs to do more about preventing the spread of invasive species. An ounce of prevention, as they say … . It is not sustainable to invest in control after a species invades. Humans are the No. 1 invasive species. It’s our responsibility, therefore, to steward the lands and prevent and correct the spread of invasive species across the landscape."
– John Hooven, University of Maryland Extension Agent Associate ^[103]

While homeowners can take some preventive measures, expert care often makes the difference. Professional arborists bring a deep understanding of tree health, pest control, and disease management ^[104][105]. They can spot early warning signs, diagnose nutrient deficiencies, and create customized care plans that homeowners might miss.

As discussed earlier, a combination of proper cultural practices and targeted treatments is essential for long-term tree health. Professional services, like Pro Landscapes MD’s Plant Health Care program, prioritize prevention through Integrated Pest Management (IPM). This approach not only identifies and addresses issues early but also ensures safety and efficiency, especially for treatments that may be too complex for homeowners to manage alone.

Regular monitoring, selecting the right tree species, and enlisting professional help form a strong defense against Maryland’s tree pests. By investing in proactive pest management, you’re not just safeguarding individual trees – you’re contributing to the health and beauty of Maryland’s entire landscape.

FAQs

What are the early signs of tree pest infestations in Maryland, and how can homeowners address them?

Homeowners in Maryland can identify the early signs of tree pest problems by watching for yellowing or browning leaves, holes in the bark or leaves, sticky sap, wood dust (also called frass), or webbing and silken tents in the branches. Regularly checking your trees is essential to catch these issues before they escalate.

To handle pests effectively, focus on maintaining healthy trees through proper watering, fertilization, and pruning. For smaller infestations, you can try removing affected branches or using natural remedies. However, if the problem becomes severe, professional treatments or carefully applied chemical solutions might be required. Be sure to follow local regulations to protect the environment and promote the long-term health of your trees.

How can I prevent tree pests from causing serious damage in Maryland?

Preventing Tree Pests in Maryland

Keeping trees in Maryland pest-free starts with consistent tree care practices. Ensuring proper watering, fertilization, and pruning not only promotes healthy growth but also makes trees more resilient against pest attacks. Another effective strategy is Integrated Pest Management (IPM), which blends different methods like planting pest-resistant tree varieties, maintaining nutrient-rich soil, and applying targeted organic or chemical treatments when needed.

Routine inspections are a must – spotting the first signs of infestation can help you act quickly, preventing pests from causing serious harm. In short, healthy trees combined with regular, proactive care are your strongest allies in protecting against common pests in Maryland.

How is climate change impacting tree pests in Maryland?

How Climate Change Fuels Tree Pest Problems in Maryland

Climate change is ramping up the presence and impact of tree pests across Maryland by disrupting their natural cycles and encouraging population growth. Warmer temperatures mean pests can emerge earlier in the spring and stay active well into the fall, giving them more time to inflict damage on trees. Take the emerald ash borer and southern pine beetle, for instance – these invasive species are thriving in Maryland’s milder winters and hotter summers, which help them survive and reproduce more effectively.

But that’s not all. Climate change also takes a toll on trees by subjecting them to drought and extreme heat, leaving them weaker and more susceptible to infestations. This creates a vicious cycle: stressed trees are easier targets for pests, which further endangers the health of Maryland’s forests and landscapes.

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