Pests and Problems

<p>Pests and Problems</p>

Boxwood Blight

The University of Illinois Extension Program has created a fact sheet for identification of boxwood blight. Download the fact sheet here.

Boxwood blight was first discovered in the United States in 2011. Currently, it has been identified in 18 states, primarily in the east. It is being managed at a state level, with various states having different regulations. Some states require nurseries to practice boxwood blight cleanliness programs to ensure the plants they sell are disease free. Here at the Chicago Botanic Garden, we are developing protocol to monitor incoming plants and to monitor our existing collection.

Boxwood blight (Calonectria pseudonaviculata)

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University,

Now that boxwood blight has been found in Illinois, and because boxwood is such a common landscape planting, we should all have a good understanding of this new pathogen. There is no need to panic, but if you have boxwoods, you should monitor them this growing season. You can find many great fact sheets online by searching for “boxwood blight” including, Best Management Practices for Boxwood Blight, from the Virginia Cooperative Extension. The Garden’s Plant Information Service can also help you with questions about boxwood blight, but we ask that you do not bring in samples. Call (847) 835-0972, or Click here to show mail address.

Boxwood blight (Calonectria pseudonaviculata) is a serious fungal disease that primarily affects boxwood (Buxus spp.), but can also hit Japanese pachysandra (Pachysandra terminalis), and sweetbox (Sarcococca spp.).

Boxwood blight causes leaf spots, stem cankers, and defoliation. The pathogen itself does not kill the plant, but weakens it to a poor state of health, allowing secondary pathogens to kill the plant. The primary means of spread is by movement of contaminated plants, but it can also be spread via pruning tools, clothing, equipment, and contaminated soil/organic matter. The pathogen can survive in soil and organic matter for years and is easily disseminated by water movement.

  • Monitor your boxwood at least one a month. Look for the following:
    • Leaf spots—light or dark brown circular lesions, often with a yellow halo
    • Stem cankers—dark brown to black cankers on the stem that can be diamond shaped or in vertical streaks
    • Defoliation—sections of the plant dropping leaves
    • If you feel you have found boxwood blight, you should contact the Illinois Department of Agriculture or send a sample to the University of Illinois Plant Clinic for diagnosis. Please do not bring suspect samples to the Garden.
  • Inspect purchased plants carefully before bringing them home.
  • Home care:
    • Plant in locations with good air circulation.
    • Prune to increase air circulation.
    • Sanitize pruning equipment before going from one plant to another. Lysol disinfectant works well.
    • Water at a time of day that allows the plants to dry quickly.
    • Avoid overhead watering if possible.
    • If using a boxwood as a hedge or mass planting, it is best to plant loosely and allow them to grow into each other; do not plant tightly.

Boxwood blight (Calonectria pseudonaviculata)

Boxwood blight photo by David L. Clement, University of Maryland,

Boxwood blight (Calonectria pseudonaviculata)

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University,

Boxwood blight (Calonectria pseudonaviculata)

Boxwood blight photo by Mary Ann Hansen, Virginia Polytechnic Institute and State University,

Giant Hogweed

Questions regarding ID of giant hogweed (Heracleum mantegazzianum) are not common in our region. This plant is not found at the Garden, and homeowners looking to identify the species and the threat of several related plants can find information and side-by-side photo comparisons on this newsletter from the University of Illinois Extension program:

Wild Parsnip

This poisonous weed is most commonly found in roadside ditches and prairie areas—not in cultivated yards and gardens. Looking similar to Golden Alexander (Zizia aurea) or a yellow version of Queen Anne's lace (Daucus carota), wild parsnip blooms later in the season, has deeply forked leaves, and has more leaflets in each compound leaf. Chemicals in the sap of the parsnip react with sunlight and cause phytophotodermatitis—a breakdown of cells and tissues when the sap on the skin is exposed to sunlight. The resulting rash is a severe chemical burn which takes many weeks to heal and may leave long-lasting scarring. It is not recommended that homeowners attempt to remove the plant themselves.

A small number of wild parsnips have been seen in the Dixon Prairie and along the Skokie River, and the Garden is taking steps to eradicate the plants.

This is certainly a plant of concern, but it should not be a reason to panic. Learn how to identify wild parsnip with this brochure from the Minnesota Department of Transportation:

According to Chicago Botanic Garden ecologist Joan O'Shaughnessy, the wild parsnip can be found at the Garden in the Dixon Prairie and along the Skokie River. "The total number of plants we managed this year was not more than 50," O'Shaughnessy explains. "We’ve used two techniques for dealing with it—pulling, and cutting. The preferred [and considerably safer] technique is pulling it after it has bloomed. The long tap root comes out with a bit of effort at this time." When visiting the Dixon Prairie, we recommend remaining on the cultivated paths.

Please contact Plant Information Service at (847) 835-0972 or via e-mail at Click here to show mail address for information about identification and removal of wild parsnip, as well as current herbicide recommendations.

Gypsy Moths

gypsy moth egg massSusceptible Plants
More than 300 species of trees and shrubs, particularly oak (Quercus), apple (Malus), linden (Tilia), birch (Betula), hawthorn (Crataegus), aspen (Populus) and alder (Alnus)

Description & Symptoms
Gypsy moths are a serious pest of forest and urban trees. Newly hatched larvae chew tiny holes in leaves in spring. Later in the season, mature larvae skeletonize leaves, and in severe cases, entirely defoliate trees. Larvae generally feed at night, hiding during the day in bark crevices or leaf litter on the ground.
Gypsy moths can be observed in all four developmental stages: egg mass, larva (caterpillar), pupa and adult moth. The egg mass is about 1½ inches long and ¾ inch wide with a buff or tan fuzzy surface. Mature larvae are about 2½ inches long, hairy, with five pairs of raised blue spots and six pairs of raised red spots. The immobile pupa is reddish-brown, leathery, and about 1½ inches long. Female moths are white or cream-colored with black markings on the wings and a wingspan of about 2½ inches. Despite their large wingspan, females cannot fly. Male moths are brown, also with black markings, and a smaller wingspan of about 1½ inches.

Timing & Life Cycle
By far the longest period in the gypsy moth life cycle is the egg mass stage. Female moths lay eggs from late July to early August on almost any sheltered surface — bark crevices, rocks, picnic tables, vehicles. Egg masses, each containing 100 to 1,000 eggs, overwinter and hatch into tiny larvae the following spring, usually in early May in the Chicago region. These larvae crawl or are blown on silk strands to the leaves of trees, where they begin to feed. The larvae go through several growth stages, eating increasingly voraciously as they get larger. By late June or early July, the fully grown larvae pupate and enter a two-week inactive stage before emerging as adult moths in late July. The moths mate, lay their eggs, and then die.

When present in high numbers, gypsy moths are a serious leaf-eating pest of hardwood trees. Severe infestations can defoliate trees, leaving them vulnerable to other insect pests, diseases, and cultural stresses. Repeated attacks over several years may kill a tree. However, healthy deciduous trees generally survive and grow a new set of leaves after being defoliated. Where moth populations are low, damage to trees often is minor and not harmful.

Treatment & Solutions
Control of gypsy moths is handled by local, state, and federal agencies, which are monitoring the spread of the moth into the Midwest from the Northeast. Homeowners can assist by searching their property for egg masses or any other signs of gypsy moths. If you live outside a quarantined area and find any evidence of the moth, call the Illinois Department of Agriculture’s toll-free Gypsy Moth Hotline at 
(866) 296-6684 for specific instructions.

In Lake County, currently the only county in Illinois under quarantine, egg masses should be scraped directly into a plastic bag, sealed, and thrown away. Tree wraps can be used to capture migrating larvae on tree trunks. Applications of biological and chemical treatments should be made only by pest control professionals.

Some tree species are less likely to be attacked by gypsy moths. These include ash (Fraxinus), dogwood (Cornus), holly (Ilex), sycamore (Platanus), tuliptree (Liriodendron) and catalpa (Catalpa). Maintaining the health and vigor of existing trees with good cultural practices helps trees withstand an infestation of gypsy moths.

For more information about gypsy moths, call the Plant Information hotline at (847) 835-0972.

Emerald Ash Borer

Recommended alternatives to replace damaged ash trees can be found in Ash Tree Alternatives.

Emerald Ash Borer


The emerald ash borer (EAB) was first discovered in the United States near Detroit, Michigan, in summer 2002. Horticulturalists were puzzled by the sudden decline and loss of hundreds of ash trees, which they attributed to a nonnative, highly destructive beetle, Agrilus planipennis, commonly called the emerald ash borer.

The EAB originated in Asia, and most likely entered the United States in packing materials such as wooden crates made out of ash. It is now believed that the emerald ash borer has been in the United States since 1990 or 1991. The EAB was discovered in Illinois in June 2006, and as of October 2012, was found in 18 states across the country and Canada. Tens of millions of ash trees have been lost due to this invasive beetle. 

PHOTO: hand holding an adult emerald ash borer (for scale)Biology and Life Cycle

Adult beetles are elongated, approximately 1/8 to ½ inch in length, with metallic green wings and bronze bodies. The EAB adults begin to emerge from ash trees as the weather warms in the spring, and can continue emerging through August. Higher numbers are normally seen in June and early July. Adult beetles live for approximately three weeks. Beetles will hide in bark crevices and will occasionally feed on ash foliage, leaving small holes along leaf margins.

PHOTO: emerald ash borer larvae.Shortly after emergence, adult beetles mate and lay eggs on the bark of ash trees (Fraxinus spp.) that are at least 1½ to 2 inches in diameter. Females will mate multiple times and can lay 60 to 90 eggs during their lifetime. Eggs hatch in approximately seven to ten days. After hatching, larvae chew their way through the tree's bark and tunnel into the cambium layer where they continue their development. The larvae create serpentine galleries that affect the tree's nutrient and water transportation system, causing it to decline and eventually die. The larvae overwinter in the tree and pupate in the spring as the weather warms. Research is currently being conducted to determine if larvae produced by late-emerging adults remain in trees for an additional year.

Adult beetles are capable of flying approximately ½ mile from infestation sites. However, they can travel much longer distances through the transportation of infested firewood and nursery stock. 


The emerald ash borer is difficult, if not impossible, to detect in low-level infestations. The only certain way to confirm the EAB is the presence of larva. The observation of one or more of the following warrants further investigation:

PHOTO: Fraxinus pennsylvanicus leaf (ash tree specimen)

Positive ash tree identification

All Fraxinus species are susceptible.

If in doubt, contact Plant Information Service for positive tree identification.

PHOTO: D-shaped exit hole left by adult ash borer.

D-shaped holes

As adults emerge in the spring, they leave distinctive D-shaped holes in tree branches and trunks that are approximately 1/8 inch in diameter. The holes may not be visible on the lower trunk or branches of the tree in less severe or recent infestations. Also, they can be difficult to detect in deeply furrowed, thick bark. The tree may require climbing in the upper canopy where bark isn't as thick for detection of the D-shaped holes. The absence of D-shaped holes does not mean that the tree is not infested.

PHOTO: Tree canopy dieback caused by emerald ash borer.

Tree canopy dieback

The EAB usually attacks the tops of trees first and proceeds downward. Most often, the tops of trees experience the worst dieback, but this is not always the case. Infested trees have been known to have sporadic dieback throughout the tree.


PHOTO: woodpecker damage from eab

Woodpecker damage

Woodpeckers often feed on the outer bark of EAB-infested trees, resulting in a "scraped" look.

Trees infested with the EAB are generally stressed due to damage and may produce epicormic shoots either at the base of the trunk or in small amounts on the main trunk.

PHOTO: Splitting bark from emerald ash borer damage.

Splitting bark

Tree bark may split vertically on trees infested with the EAB as a result of larval feeding galleries, often revealing tunnels beneath.

PHOTO: larval tunneling left by emerald ash borer.

Larval tunneling

The EAB-infested trees will exhibit larval tunneling beneath the bark.



Since 2002, when the EAB was first detected, many municipalities have removed most ash trees to reduce monetary impacts, financial restrictions, and labor intensities. Other municipalities limit ash tree removal to infested trees only.

Government quarantines play an integral role in preventing the EAB from spreading. The USDA Animal and Plant Inspection Service (APHIS) has federally restricted the movement of all ash products outside of the state of Illinois. Refer to up-to-date federal news releases. The Illinois Department of Agriculture has established quarantine zones throughout the state that regulate restricted articles, consisting of all ash tree species, the EAB adults and larvae, branches, lumber, firewood, nursery stock, roots, and green lumber, as well as composted and uncomposted wood chips. The restricted articles also include all hardwood firewood such as hickory, maple, and oak. Refer to up-to-date Illinois Department of Agriculture news releases.

In addition, the Illinois Department of Natural Resources (IDNR) prohibits transporting firewood that originated in a quarantined area to any state park, fish and wildlife area, natural area, campground, recreation area, or other property owned or managed by the IDNR.

As ash trees across the United States continue to be removed as a result of infestations, homeowners are turning to sawmills in order to reuse the lumber. A list of arborists, sawyers, and woodworkers can be found on the Illinois Emerald Ash Borer Wood Utilization Team website.

The Garden's Response

The Garden is taking several measures to protect ashes, which include about 450 in the collection. In addition, ashes make up about 20 percent of the McDonald Woods. Pesticides will be used to protect 43 key trees — two specimens each of all the primary varieties on site and in those key locations.

How to Protect Your Ash Trees

Many property managers and homeowners who own, or are charged with, the care of ash trees want to know how they can protect their trees. The first step should be to inventory and evaluate existing tree canopies with a professional arborist to gain an accurate picture of both the number of ash trees on a property and their condition. Once this inventory is complete, it will be easier to determine which trees are candidates for treatment and which are not.
Regardless of what the inventory and evaluation reveals, people with ash trees on their property in our region will need to budget for protective treatments or removal.
Currently, the most effective EAB treatment consists of systemic insecticide applications injected into the trunk of the tree or the surrounding soil. These injections spread through the vascular system of the ash tree and are ingested by the borers as they feed. While these treatments have proven successful in many cases, trees that have endured intense pressure from the EAB may not be candidates, as their vascular systems have been too badly damaged to deliver the injections to the feeding ash borers.
If this is the case, the only remedy is to remove the tree. Removal in a timely manner is important to protect property and people from falling dead branches.

Chemical Treatment

For more information and for approved insecticidal control options for dealing with the EAB, contact Plant information Service.

Periodical Cicada (17-year)

17-year cicadaPeriodical Cicada
The periodical cicada (Magicicada), is a native North American insect species inhabiting the eastern United States and, according to Penn State University, is found nowhere else in the world.

Cicadas are often mistakenly referred to as locusts. Locusts are members of the grasshopper family, which have chewing mouthparts; cicadas have sucking mouthparts and do not chew. Periodical cicadas will not bite. They have been known to land on people, but they cause no harm. Even though adult cicadas suck on plants for nutrition, they feed very little as adults.

Periodical cicadas are not the same species as annual cicadas. Even though annual cicada nymph development cycles are also very long and variable, they are not synchronized like the periodical cicadas. Annual cicadas mature at different times, which is why we see them each year. Annual cicadas are green with black and are also larger than periodical cicadas, approximately 1½ to 2½ inches in length, and appear from July to September. Periodical cicadas are black with orange wing veins and red eyes, approximately ¾ to 1½ inches in length, and appear from May to July.

The life cycle of cicadas is a mystery to entomologists. Periodical cicadas require either 13 or 17 years in the nymph stage, developing underground, and mature very slowly. They are synchronized to emerge en masse, every 13 or 17 years. Their 17-year life span makes them the longest-lived insect known. There are two races of periodical cicadas, which are distinguished by the time required to develop into adulthood: the 17-year cicadas, which appear in the north, and the 13-year cicadas, which appear in the south.

Life Cycle
The 17-year periodical cicadas last emerged in the Chicago region in 2007. Nymphs emerge from the ground when soil temperatures warm to approximately 64º F, usually sometime in May. They usually emerge from the ground after sunset, leaving behind very visible exit holes, and quickly crawl to any nearby vertical structure, preferably a tree or shrub. They shed their skins as they molt into adults, leaving behind their empty shells. Shortly after molting, their wings unfurl and their yellow-white skin darkens as their exoskeleton completely hardens.

Adults begin mating after they have completely matured, usually within a few days, and remain alive for approximately three to four weeks. Shortly after mating, females climb to living trunks, branches, and twigs, where they split the bark and deposit between 24 and 48 eggs. Adult females mate many times and are capable of laying up to 600 eggs during their lifetimes. Approximately six to ten weeks after eggs are laid, ant-like juveniles hatch and drop to the ground, where they burrow from a few inches to more than a foot into the soil. They remain underground as nymphs, feeding on tree and shrub roots for years.

Male cicadas will call females to mate by vibrating their tymbals, which are two rigid, drum-like membranes on the undersides of their abdomens. Different species of cicada produce different songs. Males respond to the calls of other males, creating a chorus of ‘singing’ cicadas that can be deafening. Females do not have tymbals and are incapable of producing the same sounds.

Susceptible Plants
Damage to woody plants occurs primarily when females split the bark on small-diameter limbs and branches for egg laying. Healthy and larger-diameter trees and shrubs can easily heal the ½- to 1-inch slits; smaller ones often wilt and die.

Developing nymphs feed on plant roots underground, which can damage trees and shrubs by reducing plant growth.

Treatment & Solutions
Newly planted and small-diameter trees and shrubs can be protected with fine netting, cheesecloth, or row-cover fabric tied securely at the base, to keep nymphs from crawling up the trunks upon emergence, as well as preventing females from slitting bark to lay eggs.

Remove small, damaged branches to keep eggs from hatching and future populations low. Also, delay planting new trees and shrubs until adult periodical cicadas are gone, usually by mid-July.

The use of chemical sprays to kill adult periodical cicadas is not recommended. Using insecticides will also kill beneficial insects that feed on harmful insects and can injure natural predators such as birds, raccoons, skunks, and moles.

Cicadas are edible; they're even considered a delicacy in many countries, as well as in different parts of the United States. Some claim that cicadas are high in protein, but recent research conducted at the University of Cincinnati’s College of Engineering has determined that cicadas may contain high levels of mercury. Diners therefore are cautioned to limit their ingestion of these "delicacies" to just a few.

White-tailed Deer

white-tailed deerSusceptible Plants
Although some plants are more deer-resistant than others, deer will eat almost any plant if they are hungry enough, especially during winters with large amounts of snowfall and high populations of deer.

Plants favored by deer include arborvitae (Thuja), yew (Taxus), rhododendron and azalea (Rhododendron), crabapple (Malus), hosta (Hosta), tulip (Tulipa), and many perennials, annuals, and vegetables.

Timing & Life Cycle
Deer browse for food year-round. They more feed heavily in the fall as they prepare for winter and as females recover from the stress of raising fawns in the spring and summer. Deer seek out plants in their most nutritious stages, which is often when they are flowering, fruiting, or undergoing rapid growth. 

Deer eat the buds, leaves, flowers, twigs, and even the bark of plants. Deer pull and tear at plant tissue as they browse for food, leaving a ragged edge rather than a clean cut. They cause further damage by trampling and sleeping in garden beds. During late summer and early fall, male deer, or bucks, remove the "velvet" from their antlers by rubbing them against tree trunks, which shreds bark and breaks branches. Velvet is the hairy skin that nourishes antlers while they are soft and growing. Bucks shed their antlers every winter. Damage can occur from ground level up to 6 feet. 

Treatment & Solutions
Choose plants that deer do not prefer. Generally, deer avoid plants with sticky, aromatic, or hairy leaves. They rarely eat ornamental grasses. However, no plant is truly deer-proof because deer will eat any plant if they are hungry.

Single fences must be at least 8 feet tall to keep deer out of a given area. A double fence system — two fences approximately 4 to 5 feet tall and 5 feet apart — is often successful because they are too wide to clear in a single jump and too close together to be jumped separately.

A number of remedies have been known to repel deer, such as hanging fragrant bar soaps or bar soaps in netted or nylon bags near favored plants. Care should be taken to assure that there are no plants located beneath the soap bags. Highly fragrant plants may also act as a deterrent. Deer located in rural areas may be repelled by hanging human hair near favored plants. Predator urines, such as bobcat or coyote, work well but must be reapplied after large amounts of rain or watering. During the summer months, sprinkler systems that are activated by motion which project a sudden hard blast of water are also very effective.
Commercial repellents may provide protection but need to be reapplied after a substantial amount of rain or watering. It is best to rotate different repellents so that deer do not become accustomed to any one product.

Please contact Plant Information Service at (847) 835-0972 or Click here to show mail address for more information about coping with deer and list of resistant plants.


Susceptible Plants
Broadleaved evergreens (boxwood, rhododendron, azalea, holly, etc.) and needled evergreens (yew, arborvitae, spruce, pine, etc.)

Description & Symptoms
Winterburn is a cultural condition that affects plants that do not lose their leaves over the winter. Leaves turn yellow and then brown in response to specific weather conditions. Leaves do not actually burn but rather dry up.

Timing & Life Cycle
Symptoms of winterburn typically appear first in late winter and accelerate in early spring. Various conditions combine to cause leaves to dry out. Mild winter temperatures and warm winter sun prompt leaves to process water, which cannot be replaced if the ground is either frozen or very dry. Winter winds also contribute to the problem. Winterburn is common after extremely cold and extremely mild winters, and in both cases it is exacerbated by lack of snow or rain in combination with strong winds and abundant sun.

Yellowing and browning leaves eventually die and will not green up, even under improved conditions. In severe cases, whole branches or sections of shrubs may defoliate.

Treatment & Solutions
Broadleaved evergreens should be planted where they will be protected from winter sun. Generally, an eastern exposure is best. In the fall, thoroughly water evergreens during dry weather until the ground freezes. Where practical, burlap screens can be constructed in the winter to provide some protection from wind and sun. In spring, wait until new growth appears before pruning out damaged areas. New growth may camouflage dead areas, making pruning unnecessary. In severe cases, plants may have to be replaced.

For more information about winterburn, call the Plant Information hotline at (847) 835-0972.

Black Vine Weevil

Susceptible Plants
Conifers, especially yew (Taxus); broad-leaved evergreens, especially rhododendron, azalea (Rhododendron), euonymus, and English ivy (Hedera); deciduous plants, including climbing hydrangea; and greenhouse plants including impatiens, cyclamen and gloxinia (Sinningia).

Description & Symptoms
Weevils are beetlelike insects that feed on plant roots in their larval stage and plant leaves in their adult stage. Adult weevils are rarely seen because they feed at night and hide during the day in dense foliage, plant litter, or mulch. The black vine weevil makes a characteristic C-shaped cut when it eats the margin of plant leaves. When insect populations are high, every leaf or needle on a plant can become notched.

Timing & Life Cycle
Adult weevils usually feed on leaves during June and early July. The larvae are most damaging in late May and early June as they feed extensively on roots before pupating into adults. Root damage occurs again in August and September when a new generation of larvae hatches underground and begins feeding on roots. There is only one adult generation per year.

The visible notching of leaves is rarely harmful to plants, although it is unsightly. Root feeding by the larvae causes more serious damage and in severe cases can kill plants.

Treatment & Solutions
It is difficult to control black vine weevil without using chemical insecticides. Insecticides are applied at the first sign of notched leaves, usually in early June.

For more information about black vine weevils, call the Plant Information hotline at (847) 835-0972.

Fall Webworm

webwormSusceptible Plants
Most deciduous trees

Description & Symptoms
Fall webworms form large, prominent whitish-gray webs at the ends of branches of deciduous trees. The location of the webs on the outer canopy distinguishes the fall webworm from the eastern tent caterpillar, which nests in webs in the crotches of trees.

Timing & Life Cycle
Webworms spend the winter as pupae in leaf litter and loose bark. In late May and June, the adult moths lay their eggs, usually on the underside of leaves. These eggs hatch into larvae, which eat leaves and form webs as they grow. By late summer, the webs are large and visible. The larvae, which never leave the webs, consume entire leaves.

Damage is minimal because the most extensive feeding occurs in late summer when trees will soon drop their leaves anyway. Although the webs can be unsightly, healthy trees are not seriously harmed by fall webworms.

Treatment & Solutions
Fall webworms have many natural predators, including birds, social and parasitic wasps, and other insects. Insecticide treatment is rarely warranted. Webs may be pruned out of trees and destroyed.

For more information about fall webworms, call the Plant Information hotline at (847) 835-0972.

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