Category Archives: Insect

Blueberry Maggot

Blueberry maggot was first detected in Wisconsin in the summer of 2016 in Adams and Sauk Counties.  This pest feeds inside blueberry fruit and caused damage in commercial blueberry production in the eastern and southern United States, as well as in eastern Canada.  This insect is expected to eventually have a significant impact on blueberry production in Wisconsin.

Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)
Blueberry maggot adult with characteristic wing patterns (left) and larva (right). (Photos courtesy of Rufus Isaacs, Michigan State University)

Appearance:  The adult blueberry maggot is a fly that is approximately 3/16 inch long and resembles a small housefly, but with dark bands on its wings.  Larvae (or maggots) are legless and can grow up to 5/16 inch in length.  Each larva has a single hook-like tooth at its mouth end.  Blueberry maggots are very similar in appearance to the closely related apple maggot, with adults of both being virtually identical in size and appearance (including wing patterns).  However, apple maggot does not feed on blueberries.

Host Range:  Blueberry (Vaccinium corymbosum) is the only commercially-grown fruit crop affected by blueberry maggot.  Wild hosts include plant species in the genera Vaccinium and Gaylussacia including wild blueberries, lingonberry, dangleberry, deerberry and huckleberry.

Symptoms and Effects:  A single larva feeds inside each fruit causing the berry to become soft as it develops.  Damage may go unnoticed until after harvest, when maggots crawl out of fruit and become visible among fresh fruit or in processed blueberry products (e.g., jams, preserves, pie fillings).

Life Cycle:  Adult blueberry maggots begin to fly in June or July, and continue to fly through August.  Females feed and mate for at least one week before they move to blueberry plants to begin laying eggs.  Females lay a single egg under the skin of a nearly ripe blueberry fruit and can lay up to 100 eggs during their approximately one month-long life span.  Eggs hatch within one week and damage from larvae generally first appears in mid-July, continuing until blueberries have been harvested.  Each maggot feeds in a single blueberry during its two- to three-week development.  After completing their development, larvae drop to the ground and overwinter as pupae in the upper few inches of soil.  A distinctive characteristic of the blueberry maggot is that, although most pupae develop to form adults by the following spring (completing one generation of the insect in a year), some pupae remain underground and do not mature for two or three years.

Monitoring:  Monitor for blueberry maggot adults several weeks before blueberries begin to ripen (usually in early June) using yellow sticky cards impregnated with a feeding attractant (ammonium acetate or ammonium carbonate).  You can buy cards that are pretreated with the attractant, or buy the cards and attractant separately and apply the attractant yourself.  Fold the sticky cards in a V-shape with the yellow side facing down and put up two traps for every five acres.  Because blueberry maggot is currently not widespread in Wisconsin, you can check cards weekly until you find the first adult.  After this initial find, check cards every few days.  Once you find an average of greater than one adult per trap for several days in a row, begin chemical treatments (see below).  Note that the feeding attractant is not specific for blueberry maggot, so you may find other types of flies on the cards – use a hand-lens or magnifying glass to positively identify any blueberry maggot adults.  Remember that blueberry maggot and apple maggot look very similar, but that apple maggot does not feed on blueberries, so flies trapped in blueberry fields/patches are most likely to be blueberry maggot.

Once you have detected adults, you can also test fruit for the presence of larvae.  Collect 100 berries from throughout your planting.  Then break the skins of the berries and mix the berries with a salt-water solution (1 part salt to 4 parts water).  Larvae will float to the surface.  The number of larvae you find represents the percentage of fruit infested.

Control:  Cultural control methods can be useful in preventing blueberry maggot infestations.  Remove weeds to eliminate habitat for blueberry maggot.  Remove wild blueberry and huckleberry plants as these can serve as alternate hosts for the insect.  Harvest fruits thoroughly and heat (to at least 120°F) or freeze any damaged or unusable fruits to kill blueberry maggot larvae.  This is particularly important if you compost fruit, because blueberry maggot pupae can readily survive in compost and serve as a source of an infestation in future years.  Clean soil thoroughly from equipment or beehives that might be moved between blueberry patches.  Blueberry maggot pupae can easily be moved in soil.

A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)
A blueberry maggot trap. (Photos courtesy of Rufus Isaacs, Michigan State University)

As noted above, start chemical control once you find an average of greater than one adult blueberry maggot per trap for several days in a row.  Alternatively, if you have had a serious problem in the past, you may want to start sprays one week after you trap your first blueberry maggot fly.  Continue sprays every seven to 10 days through harvest.  Some reduced risk active ingredients, such as novaluron, spinetoram, and spinosad are most effective when used as soon as flies are found in traps.  In addition, consider choosing a product that also provides control of spotted wing drosophila, another serious blueberry pest (see University of Wisconsin Garden Facts XHT1237 for details).  Spinosyn, spinetoram, diamide, carbamate, pyrethroid, and organophosphate-containing insecticides are effective against both insects.  Be sure to rotate use of at least two active ingredients with different modes of action to help delay development of insecticide resistance (see for details), and be sure consider the effects of sprays on non-target (e.g., beneficial insects).  Finally, because you will be spraying ripe berries, pay particular attention to the pre-harvest interval when choosing insecticides.  Check the most recent Midwest Fruit Pest Management Guide (see for complete product recommendations.

For more information on or help diagnosing blueberry maggot:  Contact your county Extension agent.

Spotted Lanternfly

Spotted lanternfly (SLF) is an invasive planthopper native to China, India, and Vietnam.  It was first detected in the U.S. in Pennsylvania in 2014, most likely arriving up to two years earlier as egg masses on materials imported from China.  As of February 2016, SLF has been confirmed in five Pennsylvania counties, but due to its highly invasive nature, it appears to be spreading rapidly.  SLF has a large host range (in Korea, over 70 plant species have been reported as hosts) and potentially could greatly impact the grape, tree fruit, plant nursery and timber industries in the U.S.

Spotted lanternfly adult (left) and nymph (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)
Spotted lanternfly adult (left) and nymph (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)

Appearance:  Adult SLFs are approximately 1 inch long and ½ inch wide when resting.  The insects’ forewings are light brown to grey with black spots at the base and have a grey net-like pattern at the tips.  The hindwings are red with black spots at the base, have white bands near the center, and have a black net-like pattern at the tips.  The heads and legs of SLF adults are black, while their abdomens are yellow with broad black bands.  When resting, adults fold their wings over their bodies and appear light brown to grey with black spots.  Adult female SLFs have a red spot at the tip of their abdomens.  SLF egg masses are 1 to 1½ inches long and ½ to ¾ inches wide, greyish-brown, covered with a grey, waxy coating, and contain 30 to 50 eggs.  First stage immature SLFs (i.e., nymphs) are wingless and black with white spots.  As nymphs mature, they eventually develop red patches, but retain their white spots.

Host Range:  SLF has a wide host range and nymphs appear to feed on leaves and branches of virtually any plant they encounter, often gathering in large numbers.  In the fall, adult SLFs gather in large numbers on tree of heaven/paradise tree, willow, maple, birch, poplar, tulip poplar, ash, oak, grape, apple and stone fruit trees (e.g., cherries and plums).  Tree of heaven/paradise tree (Ailanthus altissima) is a preferred fall feeding host for SLF adults, as well as a preferred mating and egg laying site.  This plant is an invasive species native to China that grows in disturbed sites and along roadsides.  SLF damage on grape, apple and stone fruit trees is of particular concern because these plants are important agricultural crops.

Symptoms and Effects:  SLF adults and nymphs feed on a plant’s phloem (i.e., food conducting tissue), sucking the sap from young stems and leaves, and reducing the plant’s ability to photosynthesize.  Affected plants often have weeping/oozing wounds on their trunks that eventually result in greyish-black discolorations.  Damage can lead to weakened, withered plants, and potentially even plant death.  In addition, SLFs excrete large amounts of honeydew (i.e., sugar-rich feces) which can cover stems and leaves and build up on the ground at the base of plants.  Honeydew can become colonized by sooty mold fungi (see University of Wisconsin-Extension bulletin A2637, “Sooty Mold”, available at giving leaves and branches a blackish coating that can further reduce photosynthesis and contribute to plant decline and death.  Oozing sap and honeydew also attract other insects such as wasps, hornets, bees, and ants.

Life Cycle:  SLF has only one generation per year and overwinters as eggs in egg masses.  In the spring and early summer, eggs hatch and SLFs go through four nymphal stages (called instars).  Adults begin to appear in July and August.  Males and females mate multiple times and females can produce one or two egg masses between September through November (or until they die from the onset of winter).  Female SLFs lay egg masses on smooth-barked trunks, branches, and limb bases of medium to large-sized trees, as well as on smooth stone and other natural surfaces, and on man-made items such as yard furniture, cars, trucks, and farm equipment.

A cluster of adult spotted lanternflies on tree of heaven (left), and egg masses of spotted lanternfly covered by waxy deposits (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)
A cluster of adult spotted lanternflies on tree of heaven (left), and egg masses of spotted lanternfly covered by waxy deposits (right). (Photos courtesy of Lawrence Barringer, Pennsylvania Department of Agriculture)

Scouting Suggestions:  SLF adults are poor fliers, but strong jumpers, and prefer to walk.  Nymphs and adults gather in large numbers on host plants and are easy to find at dusk or at night when they migrate up and down tree trunks.  SLFs are harder to find during the day as they tend to stay near the base of the host plants.  Beginning in late April to mid-May, watch for nymphs on smaller plants and vines, and on any new growth on trees and shrubs.  Watch for adult SLFs in late August through September, when they can be found in large numbers.  Sticky tree bands can be helpful for monitoring for young SLFs, but less useful in detecting later stage immature and adult SLFs.  From October through spring, watch for SLF egg masses (which can be very inconspicuous), particularly on tree of heaven.

Control:  To date, SLF has not been found in Wisconsin, and has been found in only five counties in eastern Pennsylvania.  These counties are under quarantine and there is an active monitoring and eradication program underway to prevent the spread of SLF.  Because SLF has great potential to adversely affect the grape, tree fruit, plant nursery, and timber industries, preventing introduction of SLF into Wisconsin is very important.  Accidental movement of egg masses poses the greatest risk for introduction.  Therefore, be sure to watch for egg masses (as well as adults and nymphs) on any item that has come from areas where SLF is established.  If you suspect that you have found SLF, please contact the University of Wisconsin-Madison/Extension Insect Diagnostic Lab at (608) 262-6510, or

For more information on spotted lanternfly:  Contact your county Extension agent or see

Viburnum Leaf Beetle

The viburnum leaf beetle (VLB), Pyrrhalta viburni, is an invasive insect that feeds exclusively on and can significantly damage Viburnum species. VLB is native to Europe and was detected in Canada in 1947. The first report of VLB in the United States was in New York State in 1996. VLB is now found scattered across much of the northeastern US. In Wisconsin, an isolated infestation of VLB was discovered in Dane County in 2009, but was successfully eradicated. In 2014, VLB was detected on a mature viburnum bush in northern Milwaukee County and other nearby infestations were detected in June 2015. At present, all active infestations of VLB in Wisconsin are in northern Milwaukee County and southern Ozaukee County.

Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University,
Viburnum leaf beetles adults (left) and larvae (right). (Photos courtesy of Paul Weston, Cornell University,
Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine;
Adult viburnum leaf beetle feeding damage (left) and egg-laying sites (right). (Photos courtesy of Paul Weston, Cornell University, and Bruce Watt, University of Maine;

Appearance: Adult VLB’s are approximately ¼ inch long and yellowish-brown in color. VLB larvae can be up to ⅓ inch long and range in color from yellowish-green to light brown with a series of black spots and dashes on their bodies.

Symptoms and Effects: VLB larvae chew holes in viburnum leaves in the spring creating a lace-like (i.e., skeletonized) pattern. VLB larvae feed individually or in small groups and can cause significant damage to viburnum shrubs. This damage can resemble the feeding damage of Japanese beetles (see University of Wisconsin Garden Facts XHT1062 “Japanese Beetle”). In late June and early July, VLB adults begin to feed, chewing oblong holes in leaves. Severe VLB infestations can cause complete defoliation of a viburnum shrub, which weakens the plant over time and can eventually lead to death.

Life Cycle: There is only one generation of VLB per year. VLB’s overwinter as eggs and development from eggs to adults takes approximately eight weeks. Larvae typically appear in early to mid-May and feed for several weeks, passing through three stages (instars) as they grow. In early to mid-June, larvae pupate in the soil and adults emerge by late June or early July. VLB females lay eggs during the summer and into October. They chew small pits in twigs, deposit five to eight eggs into each pit, and then cover the pits with tiny pieces of chewed wood to protect the eggs. Each female can deposit up to 500 eggs. Eggs remain in place through the winter until they hatch the following spring.


Cultural: When selecting viburnum plants for the landscape, DO NOT use arrowwood viburnum (Viburnum dentatum), European cranberrybush viburnum (Viburnum opulus), or American cranberrybush viburnum (Viburnum opulus var. americanum) as these types of viburnums are strongly preferred by VLB. Instead use resistant viburnums such as doublefile viburnum (Viburnum plicatum f. tomentosum), Judd viburnum (Viburnum x juddii), or Koreanspice viburnum (Viburnum carlesii). In addition, between October and the following spring, examine viburnums for twigs where VLB’s have laid their eggs. Prune and destroy these twigs to reduce VLB numbers. During the growing season encourage natural VLB predators in your area (e.g., lady beetles, spined soldier bugs, assassin bugs, green lacewings) that can reduce VLB numbers.

Chemical: Prior to bud break, apply horticultural oil to twigs where VLB eggs have been laid. This will significantly reduce the number of eggs that will hatch. Control any surviving larvae with contact insecticides such as acephate, bifenthrin, carbaryl, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin. Horticultural oil, insecticidal soap, pyrethrins and spinosad can also be effective. To achieve the best results, apply insecticides when larvae are small and before they have caused significant damage. VLB adults can be managed with contact insecticides, if needed, but are mobile and more challenging to control. Systemic products (e.g., clothianidin and imidacloprid) applied as soil drenches can also be effective, but apply these products after flowering (to minimize any risks to pollinators), but before VLB damage occurs to achieve the best protection.

For more information on viburnum leaf beetle: Contact your county Extension agent.

Zimmerman Pine Moth

Zimmerman pine moth (Dioryctria zimmermani) was first detected in the US in 1879, and has subsequently been found and is established throughout the northern US east of the Rocky Mountains. Austrian and Scots pines are preferred hosts of Zimmerman pine moth. However Eastern white and mugo pines are also attacked.

Symptoms of Zimmerman pine moth.  Tunneling by larvae in branch whorls leads to formation of masses of pitch (left).  Sap from feeding sites often runs down branches and trunks (right).  Left photo courtesy of the Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources,
Symptoms of Zimmerman pine moth. Tunneling by larvae in branch whorls leads to formation of masses of pitch (left). Sap from feeding sites often runs down branches and trunks (right). Left photo courtesy of the Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources,

Appearance: Adult Zimmerman pine moths are midsized with gray and red-brown wings, marked with zigzag lines. Larvae are generally dirty white to light grey and up to one inch long. They can only be found in pitch masses, under bark or in new shoots.

Symptoms and Effects: Zimmerman pine moth larvae tunnel into new growth causing shoot dieback, or into whorl areas causing masses of pitch to form at the wound site. Repeated attacks by the larvae cause a weakening at the area of the infestation and make the branches and trunk susceptible to breakage.

Life Cycle: Zimmerman pine moth has a one-year life cycle and spends the winter as a young caterpillar underneath bark scales of infested trees. In mid to late April, larvae become active and they migrate to the base of branches or shoots and burrow inside. Larvae continue to feed into July and then pupate within a chamber in a mass of pitch. Adult moths emerge from infested trees in late July and August, and lay eggs near wounds or preexisting masses of pitch. Eggs hatch in approximately one week and larvae feed for only a brief time before preparing to overwinter under bark scales.

Zimmerman pine moth pupa (left) and larva (right) embedded in masses of pine pitch.
Zimmerman pine moth pupa (left) and larva (right) embedded in masses of pine pitch.

Control: Avoid plant injury (e.g., construction injury) and environmental stresses (e.g., drought stress) that can make trees attractive to Zimmerman pine moth adults. Also, consider removing heavily infested trees before July to reduce the number of adults that will emerge in the vicinity of, and potentially infest, healthy trees. If opting to use insecticides to control Zimmerman pine moth, applications must be made in the spring, before larvae migrate into tree trunks. Preventive insecticide sprays should be applied as a drenching spray to trunks in mid to late April. Spraying branches and foliage is not necessary. Permethrin or bifenthrin are preventative sprays that are available for use by homeowners. Chlorpyrifos (sold as Dursban) can be used in nurseries and Christmas tree plantations. Sprays applied in early September to kill small larvae are not recommended as they tend to have only spotty success.

For more information on Zimmerman pine moth: Contact your county Extension agent.


Wireworms are the larvae of several species of click beetles that feed primarily on grasses, including grass crops such as corn and small grains. Row crops that are attacked include beans, beets, cabbage, carrots, lettuce, onions, peas, potatoes, and radishes. Asters, phlox, gladioli, and dahlias are some of the more commonly infested herbaceous ornamentals.

A wireworm larva.
A wireworm larva.

Appearance: Wireworms are thin, shiny, jointed, yellow to reddish-brown, worm-like larvae. They range in length from 14 to 112 inches and are approximately 18 wide. The different species of wireworms are distinguished by the ornamentation on the last body segment. Adults are hard-shelled, brown or black “streamlined” beetles that flip into the air with an audible click when turned upside down.

Symptoms and Effects: Wire-worms feed on seeds, hypocotyls, or developing cotyledons. This feeding activity results in reduced germination, snakehead seedlings, and wilted or stunted plants. Dead spots scattered in a planting may be an indication of wireworm activity. If the seedlings in affected areas are dug, they will be riddled with holes and larvae may be found feeding on the roots of wilted plants. Wireworms tend to be most damaging one to four years after plowing up sod, or in poorly drained lowlands, but they are not exclusive to these areas.

Life Cycle: Wireworms have an extended life cycle, taking from one to six years to complete one generation. They overwinter as either adults or larvae. Larvae inhabit the upper six inches of soil where they migrate only short distances and feed on seeds and plant roots. They are sensitive to moisture and may burrow deeply into the soil in dry conditions. Adults become active in spring and begin laying eggs. Adult females may live 10 to 12 months, spending most of this time in the soil where they may lay up to 100 eggs in sod, and grassy weedy areas in row crops. Egg hatch occurs over several days to weeks. The tiny larvae immediately begin to feed on the roots of grasses, weeds, and other crops. Because of their extended life cycles, larvae of some wireworm species will feed for two to three years before pupating. Adult wireworms that emerge from these pupae remain in the pupal chambers until the following spring.

Scouting Suggestions: Scheduled scouting is not recommended and no thresholds for wireworms have been developed. If wireworm damage is suspected, dig up several ungerminated seeds or damaged plants along with a four to six inch core of surrounding soil and check for wireworms in and around roots, or in the underground portion of stems. Larvae may be extracted from soil by washing. Bait stations may be buried in fall or spring and recovered to check for wireworm larvae.


Non-Chemical: Crop rotations that avoid susceptible crops and clean cultivation may reduce wireworm numbers. Some species of wireworms thrive in poorly drained soil and can be reduced by improving drainage. Clean summer fallowing of infested fields has been effective in some areas. Certain soil types (e.g., silt loams) are particularly susceptible.

Several natural enemies of wireworms have been described, but they are not effective in reducing populations.

Chemical: Insecticides registered for wireworm control are rarely recommended since outbreaks are infrequent. If treatment is necessary, applications should be made at the time of planting and incorporated into the soil prior to planting. Refer to University of Wisconsin-Extension publication A3422 “Commercial Vegetable Production in Wisconsin” for a list of recommended products.

For more information on wireworms: See UW-Extension Bulletin A3422, or contact your county Extension agent.



Whiteflies are not true flies although they look fly-like. They actually belong to the same order of insects as scales, aphids, and mealybugs: the order Homoptera. There are several species of whiteflies that can infest greenhouses including the greenhouse (Trialeurodes vaporariorum), sweet potato (Bemisia tabaci), silverleaf (Bemisia argentifolia), and bandwing (Trialeurodes abutilonea) whiteflies. Of these, the greenhouse whitefly is the most common in northern areas. The silverleaf whitefly is responsible for causing phytotoxemia in poinsettia as this species extracts more sap than the other species. Bandwing whiteflies can enter the greenhouse in late summer or early fall but are not as much of a problem as previously mentioned species. Host plants include fuchsia, geranium, hibiscus, gerbera daisy, and poinsettia. Vegetable hosts include cucumbers, tomatoes and eggplant.

An adult whitefly.
An adult whitefly.

Appearance: Whitefly adults resemble tiny moths and are covered with a whitish powder. Species identification can be made by examining the wing markings. The first instar nymphs resemble scales, but they become a transparent yellow-green and settle once they reach the second and third instar stages.

Symptoms and Effects: Like all other Homopteran insects, whiteflies have piercing-sucking mouthparts and feed on plant juices. Damage consists of yellowing and wilting of the foliage. In severe cases, plant death may occur. Whitefly infestations in vegetable crops will produce a noticeable yield reduction. Honeydew and sooty mold may also be present if populations are large enough. Whiteflies are capable of transmitting viruses to some hosts, but at the present time, this is not a major concern.

Life Cycle: Female whiteflies lay six to 20 eggs per day on the lower leaf surface of host plants. The eggs are white initially, but become dark brown as they mature. Eggs hatch in seven to 10 days and the mobile, first instar crawlers resemble scales. Within several hours of hatching, these crawlers will seek out a suitable place to settle, where they will pass the next two instars. The final instar is often referred to as a pupa although the whiteflies go through simple metamorphosis in which a true pupal stage is absent. There can be several generations of whiteflies per year, with each generation taking one to three months to develop depending on the temperature of their environment. At 82°F, whiteflies develop from egg to adult in 18 days.

Scouting Suggestions: Check hanging baskets frequently and monitor any weeds that may be growing beneath greenhouse benches. Begin monitoring susceptible crops such as fuchsia and poinsettia at planting. Yellow sticky traps placed just above the crop canopy will help you monitor adult whiteflies, as will a gentle shaking of the foliage. A more thorough visual inspection of the foliage is necessary to detect whether immature nymphs are present. Placing trap crops such as fuchsia near doors and air-intake vents can signal when whiteflies are moving into the greenhouse.


Non-Chemical: There are no established treatment thresholds, but plants can handle more whiteflies than greenhouse managers can tolerate. Typically a mature poinsettia plant can tolerate up to 50 whiteflies per leaf before damage occurs.

Good sanitation and exclusion are critical for whitefly management. Eliminate all plants including weeds and “pet” plants for at least one week before starting a new crop. Inspect all new plant shipments. Screen vents to keep bandwing whiteflies from entering the greenhouse in the fall. Avoid excessive fertilization and irrigation.

There are several parasitic wasps that control whiteflies. The most common is Encarsia formosa which is commercially available. Other available natural enemies are Encarsia luteola, Eretmocerus eremicus, Chrysoperla comanche, Chrysoperla rufilabris, Delphastus pusillus, and several minute pirate bugs (Orius spp.).

For additional information on biological control, refer to NCR publication 581, “Biological Control of Insects and Other Pests of Greenhouse Crops”.

Chemical: There are several insecticides available for control of whiteflies. Refer to UW-Extension publication A3744, “Insect Pest Management for Greenhouses”, for a complete listing of available products. Whitefly management is difficult without pesticide use. It is critical that you rotate chemical classes to prevent an outbreak of insecticide-resistant populations. Start any chemical control program early and treat every five to seven days for a total of three treatments to control all stages of overlapping generations. Watch closely and evaluate for the development of resistant whitefly populations. If you find you aren’t getting suitable control with one class of insecticide, switch to another.

For more information on whiteflies: See UW-Extension Bulletin A3744, or contact your county Extension agent.

White Grubs on Christmas Trees

White grubs (i.e., larvae) of the common May/June beetle or “Junebug” (Phyllophaga spp.) are an important pest of Christmas trees in Wisconsin. This soil-dwelling pest feeds on the roots of pines, firs, and spruces, and can cause damage severe enough to kill small trees in Christmas tree production fields.

A typical white grub (left) and an adult May/June beetle (right).  (Adult photo courtesy of Phil Pellitteri)
A typical white grub (left) and an adult May/June beetle (right). (Adult photo courtesy of Phil Pellitteri)

Appearance: Adult May/June beetles are typically ½ to one inch long and vary in color from reddish-brown to almost black. Adults are active in late May and early June, often flying near house lights at night. May/June beetle white grubs have a distinctly C-shaped, cream-colored body with a reddish brown head and three pairs of legs. Grubs vary in size (depending on their stage of development), and can be up to 1¼ inches long when fully mature. Larvae have strong mandibles (i.e., mouth parts) that they use to chew on the roots of small trees.

Symptoms and Effects: Adult May/June beetles occasionally cause damage to trees by feeding on leaves and needles. In contrast, May/June beetle larvae can be extremely damaging to young conifers. White grubs damage young trees by feeding on their roots and interfering with the uptake and transport of water and nutrients within the trees. The initial symptoms of grub damage appear similar to those of drought stress: mild yellowing and wilting of trees. When feeding damage to roots is severe, trees turn brown, often shed needles and typically can be pulled easily from the ground. Small conifers (e.g., 2-2 or 3-0 trees) in Christmas tree production fields are often most susceptible to white grub damage due to their small root systems. In contrast, larger trees with more developed root systems can tolerate some white grub activity without major consequences.

Life Cycle: May/June beetles typically have either a two- or three-year life cycle in Wisconsin depending on species. Adults emerge in late May to early June and are active in the evening hours. Adults mate, and females lay eggs in the soil. After emerging from eggs, white grubs begin to feed below-ground on plant roots. Larvae pass through three stages (called instars) and become progressively larger and more damaging. Depending on the species of May/June beetle, larvae begin pupating in the soil in the late summer and fall of the either the second or third year of their life cycle. The next generation of adults emerges the following year.

Heavy feeding activity by white grubs can destroy the root system of small conifers.
Heavy feeding activity by white grubs can destroy the root system of small conifers.

Control: An integrated approach to control that includes cultural, physical and chemical practices can help prevent or at least minimize the effects of white grubs. Control practices should include the following:

Scout fields prior to planting to identify potential white grub problems. Not all fields have problems with white grubs. If you sample with a hand trowel and find average grub densities of ½ to one or more grubs per square foot, grub control measures are warranted. Similarly, if you sample with a tree planter and find grub densities of approximately 1½ to three or more grubs per ten linear feet, grub control measures are warranted.

Apply insecticides when white grub densities are high to help prevent root damage to small trees. Grub control products for Christmas tree farms include products containing bifenthrin, imidacloprid, and thiamethoxam. You can directly apply these insecticides into the root zone of trees via soil incorporation or root dipping, or apply them as banded sprays. If you opt for a spray treatment, be sure to use a relatively high spray volume (i.e., 44 to 220 gallons/acre), and apply the insecticide prior to a forecasted rain to ensure proper movement of the product into the soil profile.

Manage weeds in production fields using a chemical herbicide. This will deter May/June beetles from laying eggs in the treated area. Female May/June beetles prefer to lay eggs in weedy or mowed grassy areas.

For more information on white grub control on Christmas trees: Contact your county Extension agent.

Western Conifer Seed Bug

Western conifer seed bugs belong to the leaf-footed bug family Coreiidae. Adults are 34 of an inch long, elongate, reddish to dull brown with a faint, white zigzag straight line across the center of the wings. They have long, thin antennae and hind legs that are flattened (leaf-like). Western conifer seed bugs can fly readily and may make a buzzing noise if disturbed. Western conifer seed bugs also have well developed scent glands that emit strong pine-like odors. For that reason they are sometimes incorrectly called stink bugs. Western conifer seed bugs are also often mistakenly identified as assassin bugs.

A Western conifer seed bug.
A Western conifer seed bug.

Western conifer seed bugs have become more numerous in Wisconsin during the last five years. They can become a nuisance when they crawl up the sides of buildings during September and October. Sometimes they cluster in small groups and enter buildings at the onset of cold weather as they seek a protected site to spend the winter. If they can crawl under siding or through other openings into the home, these insects will overwinter in the house and re-emerge on warm, sunny days during the winter and spring months. Western conifer seed bugs do not bite or cause damage in the home.

Life cycle: Usually a single generation of Western conifer seed bugs occurs each year. Western conifer seed bugs have a piercing, sucking moth part, and nymphs (immature insects) feed by sucking nutrients from the seed cones of white, red, Scots, Austrian, and mugo pine, white spruce, Douglas fir and hemlock. This feeding damage does not hurt the tree, but reduced seed production may result from heavy infestations.

Control: The first line of defense against Western conifer seed bugs is to prevent their entry into the home. Screen attic, overhang, and wall vents to mechanically block points of entry for the insect. Eliminate or caulk gaps around door and window frames and soffits, and tighten loose-fitting screens, windows or doors. Insecticidal soap sprays or general insecticides can be used to kill insects clustered on the outside during the fall. When adults find their way indoors, simply vacuum or hand-remove them.

For more information on Western conifer seed bugs: Contact your county Extension agent.


The term webworm is used to describe several insects whose caterpillars use silk to join plant parts together to form protective nests. Two common insects that create nests in fruit and woody ornamental trees are the eastern tent caterpillar and the fall webworm. These insects should not to be confused with the forest tent caterpillar, whose name is a misnomer, because it does not make a tent. Both eastern tent caterpillars and forest tent caterpillars are often mistaken for gypsy moth larvae because of their similar appearance.

Plants Attacked and Damage: Hosts of the eastern tent caterpillar, fall webworm, and forest tent caterpillar are similar. Eastern tent caterpillars prefer plants in the rose family (Rosaceae) such as wild and landscape cherry, apple, crabapple, plum, and peach, but have also been found in ash, birch, willow, maple, oak, and poplar. Eastern tent caterpillars are generally active from April until early June, and they typically make their nests in the forks of branches when leaves are newly developing. Fall webworms feed on almost all shade, fruit, and orna­mental trees except conifers. They are active from July through September, and typically make their nests in branch tips. Forest tent caterpillars prefer wild cherry, but also feed on oak, maple, hawthorn, and numerous other shade trees. Forest tent caterpillars do not make nests, but feed in the upper portion of trees on expanding flowers, leaf buds, and eventually foliage.

Eastern tent caterpillar (left) and fall webworm (right). (Fall webworm photo courtesy of David J. Shetlar.)
Eastern tent caterpillar (left) and fall webworm (right). (Fall webworm photo courtesy of David J. Shetlar.)

Control: Eastern tent caterpillars, fall webworms and forest tent caterpillars rarely reach large enough populations in ornamental trees to cause serious damage. Typically, trees can recover from feeding damage. However, nest and feeding damage can lower the aesthetic value of a tree. In addition, repeated defoliation year after year may contribute to tree decline. On small trees, webworm nests can be removed or pruned out. Simply scrape or prune the nest off onto the ground and crush to destroy the caterpillars. Remove nests in the early morning or late afternoon because more caterpillars are located in nests at these times. In larger trees, insecticide treatments may be necessary. Treat small, young caterpillars while they are inside the nest in the morning or late afternoon.

For pesticide recommendations: See UW-Extension Bulletin A3597, or contact your county Extension agent.

Viburnum Borer

Major branch dieback, plant decline, and plant death on Viburnum species in Wisconsin are commonly associated with the caterpillars of clearwing borer moths. Heavily infested plants appear unhealthy, and often show swelling, cracks and emergence holes at the base of the plant.

Viburnum borer damage: Dieback on a shrub (left) and close-up of damage on a lower stem (right).
Viburnum borer damage: Dieback on a shrub (left) and close-up of damage on a lower stem (right).

Two species of clearwing borer moths, the viburnum clearwing borer, Synanthedon viburni and lesser viburnum borer, Synanthedon fatifera, attack from ground level to about 18 inches above the base of American highbush cranberry and other Viburnum species. Gnarled and scarred stems with sawdust are sure signs of attack. Swellings and callus growth indicate the healing of old injury sites or long standing damage.

Life cycle: Adults of both the viburnum clearwing borer and the lesser viburnum borer are day flying moths that mimic the flight and appearance of wasps. They are bluish black with yellow markings, clear wings and a wingspan of 34 inch. Larvae are pinkish white caterpillars with reddish brown heads. During late June and July, adults emerge from infested plants and deposit eggs on bark near wound sites. Larvae tunnel into the bark and cambium, but do not enter the wood. Over time this tunneling will cause distortions and swellings on the main stems and branches.

Control: Strong vigorous plants are less attractive to borers and more likely to survive attack. Good plant maintenance (e.g., prevention of bark injuries and wounds) will reduce problems. Nursery owners should pay close attention to differences in cultivar susceptibility. Plants that require high maintenance and yearly pesticide treatments should not be produced for sale.

Chemical control is targeted during the adult moth egg-laying period. Larvae under the bark are protected from treatments. Pheromone traps can be used to monitor the first adult activity in spring, and to help time insecticide sprays. Use a spray containing the insecticide permethrin and apply the product from the ground level to about 18 inches up the stem. If traps are not available to aid in the decision-making process, apply insecticides during mid-June and in heavy infestations reapply in mid-July.

For more information on viburnum borer: Contact your county Extension agent.

Thanks to Karen Delahaut and Chris Williamson for reviewing this document.