Insects

The Challenges of Boxwood: Pests, Diseases, and Alternatives

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By Marie Woodward, UConn Home & Garden Education Center

Boxwood, a classic choice for formal gardens and hedges, has faced increasing threats in recent years. As gardeners grapple with these challenges, it is crucial to understand the issues at hand and explore alternative plants for our landscapes.

Boxwood Blight is an aggressive fungal disease that affects various Boxwood species and causes rapid defoliation and potential plant death. First identified in the United Kingdom in the mid-1990s, this disease has since spread across North America. Early symptoms include stem cankers, sunken lesions, and eventual dieback. To mitigate the risk of Boxwood Blight, choose resistant cultivars, practice good garden hygiene, and monitor your plants for early signs of infection.

The Box Tree Moth is an invasive pest native to Asia that feeds on Boxwood plants. Since its arrival in North America, this moth has wreaked havoc on Boxwood populations, leading to defoliation and plant stress. Symptoms of infestation include see-through plants, "stick shrubs," and stem cankers. Regular monitoring and integrated pest management strategies are essential for controlling this destructive insect.

As Boxwood plants continue to face challenges from pests and diseases, it is wise to consider alternative options for our gardens. Ilex crenata (Japanese Holly) is a versatile, broadleaf evergreen that can be shaped into hedges or topiaries. Its small, glossy leaves provide a neat appearance, and its adaptability to various soil types and sun exposure makes it a low-maintenance choice.

Row of Gem Box Ilex shrubs for sale
Gem Box Ilex is one of many fantastic substitutes for Boxwood shrubs. Photo by H. Zidack

Euonymus japonicus (Japanese Euonymus), an evergreen shrub with small, glossy leaves and tolerance for a range of growing conditions is another possible substitution. Its compact growth habit and easy maintenance make it an excellent choice for hedges or screens.

Ilex glabra (Inkberry), is a slow-growing evergreen native to North America, featuring dark green leaves and red berries in the fall. Its low, spreading habit makes it ideal for low hedges or mass plantings.

Privets (Ligustrum), are fast-growing, low-maintenance evergreen shrubs with small, glossy leaves. They can be used for hedges, screens, or as stand-alone specimens. However, keep in mind that three cultivars, border privet, (Ligustrum obtusifolium Sieb. & Zucc), California privet, (Ligustrum ovalifolium Hassk.) and European privet (Ligustrum vulgare L.) are listed on UConn’s invasive plant database.  If you decide to plant privets, look for seedless cultivars such as Golden Ticket privet (Ligustrum x vicaryi "KCLX1") at your local nursery.  

The Boxwood Blight and Box Tree Moth present ongoing challenges for gardeners and landscapers. By understanding these threats and adopting appropriate management strategies, we can mitigate the damage they cause. Additionally, exploring alternative plants can help create more resilient and sustainable gardens in the face of these challenges. With careful planning and thoughtful plant selection, our landscapes can continue to thrive in the face of adversity.

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For questions about your boxwoods or other gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations.

This article was published in the Hartford Courant Feb. 22, 2025
It was been updated from its original publishing on Feb. 27, 2025

The Fall Invasion of the Asian Lady Beetle

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By Marie Woodward, UConn Home & Garden Education Center

multi-colored Asian ladybeetle on a flower

As the leaves change color and the weather turns colder, many people look forward to the beauty and coziness of autumn. However, one uninvited guest often accompanies the season: the Asian lady beetle. This insect, scientifically known as Harmonia axyridis, can be a nuisance to homeowners as it seeks shelter in warm buildings during the fall months.

The Asian lady beetle is native to eastern Asia but was introduced to the United States and other parts of the world in the early 20th century as a biological control agent for aphids and other pests. While they are highly effective at controlling these pests in the gardens and crops, their rapid spread and tendency to congregate in large numbers have caused problems for homeowners.

These beetles are easily recognizable by their orange to reddish-brown coloration, small black spots on their wing covers, and distinctive M-shaped marking behind their head. Their size ranges from 5-8mm in length. They have six short legs and two antennae.

During the fall, the Asian lady beetle seeks protected locations to spend the winter. They gather in large groups, often on the sunny side of buildings, before ultimately finding their way into homes and other structures through cracks and gaps. It is not uncommon to find them gathered in attics, wall voids, or other quiet, undisturbed areas.

Once inside, these beetles can become a nuisance due to their sheer numbers and tendency to release a yellowish, foul-smelling liquid when disturbed. This liquid can stain walls, fabrics, and other surfaces, and may cause allergic reactions in some individuals. Additionally, some people find the beetles’ scent unpleasant or even nauseating.

Prevention is key to avoiding an Asian lady beetle infestation. Sealing entry points, such as cracks around windows, doors and utility openings, can significantly reduce the likelihood of an invasion. Additionally, keeping exterior lights off at night and planting trees or shrubs away from the house can reduce the attractiveness of your home to these insects.

If beetles have already found their way inside, using a vacuum cleaner is the best means of removal. However, be sure to dispose of the vacuum bag or empty the canister outdoors immediately to prevent the beetles from returning back into your home. Alternatively, insect light traps or sticky traps can help capture and remove beetles.

It’s essential to remember that while the Asian lady beetle can be a nuisance, it is not a significant threat to your home or your health. Taking proactive measures to prevent their entry and managing their presence can significantly reduce the annoyance caused by these uninvited guests.

As the fall season arrives, keep in mind the potential for Asian lady beetles to seek shelter in your home. By understanding their behavior and implementing preventive measures, you can enjoy the beauty and warmth of autumn without the invasion of these pesky insects.

If you have questions about Asian lady beetles or other gardening topics, contact the UConn Home & Garden Education at (877) 486-6271 or www.homegarden.cahnr,uconn.edu or your local Cooperative Extension Center.

Current Landscape and Garden Conundrums

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By Pamm Cooper, UConn Home & Garden Education Center

Here at the UConn Home & Garden Education Center we have been getting questions about three pests that have been particularly widespread in the state. Whether in the landscape or the garden, there is always something going on, good or bad, and keeping up with pests or perceived pests can be challenging. The following reflect the most common inquiries we have had over the past few weeks.

Asiatic garden beetles found in a spoonful of soil
Photo by Pamm Cooper

Asiatic garden beetles have been a real problem for many gardeners this year. An imported pest, these small, rusty brown, night-feeding pests can devastate plants overnight then disappear during the day. Leaving you to wonder what is eating your plants. Favorite plants include dahlias, basil, zinnias, sunflowers, peppers, eggplants and goldenrods. They will feed on over 100 herbaceous and woody plants. In the evening a plant can look great, and the next day it can be a skeleton of stems and leaf veins.

Check damaged plants at night with a flashlight; if they are active, you should find them. During the day, dig an inch or so into the mulch and soil under damaged plants. These beetles will hide there during the day. Some people have reported finding as many as 300 in a night, then 50 each night, until they find few or none. New beetles will fly in daily, so be vigilant. Feeding by adults should end by the end of August. Crush them or put them in a container of soapy water until they succumb. Foliage can also be treated with an appropriate insect control product that will kill them after they feed on the leaves, Read and follow label instructions carefully for any control products if they are needed.

Cicada killer holding a Cicada
Photo by Pamm Cooper

Cicada killers are rather mild-mannered (like Clark Kent) burrowing wasps that can cause alarm when they appear in the summer months. These wasps are very large, and females have the potential to sting, but have no aggressive nest-guarding instincts as do most other wasps or bees. What they have is size, and so become easily feared, especially when they burrow along sidewalks or other sandy areas close to pool, gardens and houses.

Female cicada killers burrow a rather rectangular tunnel deep into soft soils into which they will eventually drag a cicada they have paralyzed. They lay one egg on the victim and the larva will feed on the carcass and pupate over the winter. They may be a chronic problem in areas of sandy soils and can be discouraged by disrupting tunneling activity by drenching areas where they are actively tunneling with water. They do not like moist soils, so this may be the only control method needed. Digging may disrupt root systems of plants if the tunnels are made at the base of plants, and watering the plants affected in this way may settle the soil back around the roots. Use of any pesticide would only be effective if wasps are still going in and out of tunnels and should be used only if necessary.

The final pest we will cover are aphids. These piercing-sucking feeding type insects are small, but they can occur, seemingly overnight, in large numbers on plants. Aphids prefer newer growth like upper stems but are not so fussy later in the year when they feed on flower buds, old and new leaves and flower stems. Later in the summer some species may cover older stems right down to the ground. This is especially a problem on common and swamp milkweeds. Aphid feeding can cause wilting of plant parts above where heavy feeding occurs. Leaves can be mottled, then become distorted before turning brown.

Red aphids on a stem
Photo by Pamm Cooper

Control of aphids relies on paying attention every day. Aphid females can give birth to live young during the summer, often fifty or more new aphids appear from each female per day. This is why control seems effective, then before you can say “my plants look really good now”, there are scads of aphids back where they were before. Aphids in high numbers, especially on sturdy stems, can be crushed by hand, sprayed with a suffocating type product like insecticidal soap, or knocked off by a strong jet of water. Keep in mind that the reproductive females have wings, and they will take flight at the first sign of trouble. That is why they can persist on plants.

If aphids are a serious issue on plants, with no control measures apparently working, consider removing the affected plants and adding plants you know they so far have shunned as a food source. It may be a painful but necessary step.

Be alert to what is happening in your own backyard, for it is certain something, good or bad, is going on. The sooner you discover the bad, the better. Know that: “On every stem, on every leaf, and at the root of everything that grew, was a professional specialist in the shape of grub, caterpillar, aphis, or other expert, whose business it was to devour that particular part. “~Oliver Wendell Holmes

For questions about garden pests or any other gardening questions, feel free to contact us, toll-free, at the UConn Home & Garden Education Center at (877) 486-6271, visit our website at www.homegarden.cahnr.uconn.edu

What’s Eating My Brassicas?

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By Dawn Pettinelli, UConn Home & Garden Education Center

Broccoli, cabbage, kale and other members of the brassica family are tasty and so good for you but its not just us who find them delectable. Brassicas have a number of insect pests but probably several caterpillar species do the most damage.

A close up of caterpillar damage on broccoli leaves.
Caterpillar damage on broccoli. Photo by dmp2024

When checking plants, look for holes in the leaves. A few irregular holes may soon become a skeletonized leaf with only the midrib left if control measures are not taken. These caterpillars can quickly devour plants.

Two of the most common pests are the imported cabbageworm and the cross striped cabbage worm. According to Dr. Shuresh Ghimire, UConn Vegetable Extension Specialist, imported cabbageworm is the offspring of the cabbage butterfly, a butterfly with white wings with 1-2 round black spots on the forewing. Eggs, laid singly on leaves, are light green or yellow and slightly elongated. Three to 5 days later, the eggs hatch. The lime green velvety caterpillars feed for 2 to 3 weeks.

Dr. Ghimire noted that imported cabbage worm feeding and resting mostly occur on the underside of leaves. Be sure to check both the tops and bottoms of leaves. Damage includes round or ragged feeding holes and deposits of wet, green or brownish frass. There can be 4 to 5 generations each year. This pest overwinters as a pupae close to host plants.

Cross stripped cabbage worm
Cross striped caterpillar. Photo by dmp2024

The cross-striped cabbageworm used to be a southern pest but no longer. The adult moths fly at night so are seldom seen. Cross-striped cabbageworms are most abundant on late-season plantings says Dr. Ghimire. Unlike the other major caterpillar pests, such as cabbageworm and diamondback moth, the cross-striped cabbageworm lays its eggs in batches (3-25) rather than singly, so caterpillars emerge in clusters. Egg batches are yellow, flattened, overlapping like fish scales, and attached to the lower leaf surfaces.

The distinctive-looking caterpillars are bluish gray on top with green on their undersides, a yellow stripe on each side with a row of numerous black bands across the back. Clusters of these caterpillars are voracious feeders and plants infested with cross-striped cabbageworm larvae are often completely skeletonized, while adjacent plants may be left undamaged. There are 2 or 3 generations per year.

Two other caterpillar pests of brassicas are the diamondback moth and the cabbage looper. Eggs of these two pests are laid singly and most years they do not cause considerable damage to home vegetable gardens.

There are several strategies to control these caterpillars on broccoli plants. If you have just a few plants, check them every few days looking at both sides of the leaves and either squish any caterpillars you find or drop them into a can of soapy water.

A close-up of a leaf with chewing damage
Caterpillar damage on brassica leaves. Photo by dmp2024

Rotating your plantings and interplanting with flowers may confuse pests. Dr. Ghimire suggests planting flowers to attract natural enemies, like Braconid wasps, which lay eggs on soft-bodied caterpillars such as cabbage worms. The larvae feed inside the live caterpillars, weakening or killing them. Some plants known to attract pest predators include dill, parsley, hyssop and mints.

Since brassicas do not need to be pollinated, they can be covered with netting or row covers to exclude insect pests. The holes in the netting should be one-quarter inch. Hoops can be used to hold up the barrier or one can make wooden or PVC cages for a custom fit. Be sure to tuck or pin the edges to the soil so pests can’t crawl under.

Finally, if the caterpillar infestation becomes too extensive, Dr. Ghimire recommends Bacillus thuringiensis (Bt), which is a biological control for Lepidoptera species of moths and butterflies. Bt is a bacterium that when sprayed on your plants and consumed by the caterpillar enters the insect’s gut and causes it to die. While it is effective for controlling these pests, it is harmless to humans and other animal species. Limit its use to brassicas to prevent it from affecting desirable caterpillars.

As with all garden pests, the key to healthy plants is regular monitoring and putting control measures into practice when pests are first noticed. For questions on brassica pests or any other gardening questions, feel free to contact us, toll-free, at the UConn Home & Garden Education Center at (877) 486-6271, visit our website at www.homegarden.cahnr.uconn.edu

Seen any Sawflies?

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By Dawn Pettinelli, UConn Home & Garden Education Center

Hibiscus sawfly larvae on hibiscus leaf. Photo by dmp2024

Gardeners know that amidst the promises of each new growing season come its challenges, usually in the form of weather or pests. A common insect pest this time of year are sawfly larvae, which feed on some of our favorite plants including roses, azaleas, perennial hibiscus, dogwoods, and some pines. If populations are high, significant damage can occur.

Sawfly adults are small, short-lived insects slightly resembling wasps to which they are related but their waists are generally thicker. Their ovipositor (egg-laying appendage) is somewhat saw-like in appearance, hence their common name. Eggs may be laid singly or in groups.

Larvae look like small caterpillars but there is a distinctive difference between caterpillars in the Lepidoptera family that transform into butterflies and moths, and sawfly larvae in the Hymenoptera family. Larvae in both families have numerous pairs of legs. From the head, the first three pairs are thoracic legs that correspond to an adult insects’ three pairs of legs. Count the number of fleshy leg pairs (pro-legs) after that. Caterpillars have 5 or less pairs while sawfly larvae have 6 or more.

Rose slug damage on rose leaves
Rose slug damage on rose leaves. Photo by dmp2024

Check your rose bushes for rose slugs, a common name for at least 2 species of sawflies whose larvae may be feeding on your plants. One is thought to be native to the U.S. and the other accidentally introduced from Europe. Both were noticed as pests in the Boston area over 100 years ago and do similar damage to rose foliage.

The small green caterpillar-like larvae that may be ½ to ¾ inch long depending on the species skeletonize the leaves and only the veins remain. They can feed for several weeks if not controlled and move to the undersides of the leaves during the day making them hard to spot. One or two generations may be present each season, again depending on species. Mature larvae will pupate in the soil below plants, where they overwinter and will reemerge the following spring.

Hibiscus sawflies feed on members of the mallow family with the most common one in this area being the large-flowering perennial hibiscus. The green larvae are small, and also can be found on the undersides of leaves where they often go undetected until large leaf areas are consumed.

There are at least 3 species of sawflies that feed on azaleas in this area. The small green larvae have tannish heads but are hard to spot at first as they feed on emerging foliage. Keep an eye out for foliar feeding at the edges of the leaves. The larvae are less than ½ inch in length and feed until late June or early July. There is only one generation per year and these larvae will also drop to the ground to pupate and overwinter in the soil below plants.

Pine sawfly species seem to prefer Mugo, Scots and red pines although they can feed on others. Some are inadvertently introduced pests like the European pine sawfly. Since they were first noticed around 1925, they have become widespread pests. The larvae may be up to an inch long and is grayish-green with mostly darker parallel stripes. Red-headed pine sawfly larvae have red heads as the name indicates but has a yellow body with black spots.

Pine sawfly adults typically lay groups of eggs so multiple larvae hatch and feed in groups. They have a very distinctive defense mechanism when disturbed. Most curiously they rear up and ‘wave’ as you wave your hand over them. This does discourage insect, avian and vertebrate predators, at least to some extent.

Dogwood sawfly females can lay more than 100 eggs on the underside of their preferred grey dogwood host plant. Larvae can consume the whole leaf as they mature leaving only the large midvein. Young larvae are translucent and yellowish but develop black spots and become covered with a white powdery coating as they mature. Their appearance can make a gardener think there are two species of insects attacking plants rather than one. When mature, the larvae seek out an overwintering location with rotted wood on the ground being preferred.

Regardless of which species of sawfly is attacking your plants, options for control include hand picking, insecticidal soap, Spinosad or other insecticides labeled for sawflies. While Bacillus thuringiensis (BT) can be used for caterpillars in the Lepidoptera family, like cabbageworms and Eastern tent caterpillars, it does not work on sawflies.

If you have questions on identification or control of sawfly larvae or any other gardening questions, feel free to contact us, toll-free, at the UConn Home & Garden Education Center at (877) 486-6271, visit our website at www.homegarden.cahnr.uconn.edu

 

Eastern Tent Caterpillars

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By Pamm Cooper, UConn Home & Garden Education Center

Eastern Tent Caterpillar Tents in a tree

Eastern tent caterpillars, Malacosoma Americanum, are native to North America and are noticed mainly because of the silken tents they build in the forks and crotches of trees in early spring. While most tents are found on black cherries, they can also be found on other trees such as apple and crabapple. They are readily visible since tents are constructed before leaves fully expand. There is only one generation per year.

These caterpillars are hairy and dark when small, and later instars have two yellow lines along the back. A white medial stripe goes along the sides of the body, and this is flanked by two yellow lines. There are blue blotches along its side as well. Bottom hairs on the body are rusty brown. Forest tent caterpillars are also hairy, but they do not make tents, and their bodies

are blue with white dots on the back. Handling should be done with gloves on as some people may have sensitivity to the hairs.

Egg masses are black, laid on small branches of host trees the previous year, and the egg mass rings around the branch. Sometimes they are mistaken for small black knot galls. 150-300 eggs may be in each egg mass. Caterpillars typically hatch as black cherry leaves begin to expand the next spring. Caterpillars feed on leaves and buds and rest communally by day in the nests they construct from silk.

While they can almost defoliate small trees, these caterpillars usually have completed their feeding stage in time for the trees to put out new leaves by early summer. The more tents there are on small trees, though, the greater number of caterpillars there are, so damage will increase.

While protected from many predators while inside the tents, there are birds that will tear the tents apart to feed on the caterpillars inside. Both the black-billed and the yellow-billed cuckoos are known for their ability to do this, and native vireos will also seek out and rip apart the tents.

Mature caterpillars leave the host plants in early summer in search of suitable sites to pupate within a silken cocoon they will spin. Moths emerge later that year. The moths have a fluffy light brown body, and the wings have three bands with the center being narrower than the outer bands and a lighter brown in color. The center band is bordered on both sides by thin, creamy bands.

Eastern Tent Caterpillar Tents in a tree

Occasionally, eastern tent caterpillars have outbreak years where large numbers of the tents can be seen on the same tree. Fresh buds may also be consumed if trees are severely defoliated. When found on residential properties, tents can be swept apart by rakes or brooms, exposing caterpillars to predators, or knocking them off the trees. If warranted, foliage can be sprayed with a biological product called Bacillis thuringiensis subspecies, Kurstaki, or BtK, which only harms caterpillars and not other insects. Caterpillars will ingest the product as they feed on the foliage.

Most healthy trees can tolerate severe defoliation from eastern tent caterpillars. If concerned, look for egg masses in the winter on trees that had been damaged the previous spring. Remove them, if possible, or crush them, or prune the branch off below where the egg mass is found. Or let them be if the trees appear to have recovered. Letting nature take its course with native insects on native trees can often benefit birds and other predators. Do not confuse them with the notorious gypsy moth caterpillars which do not make silken tents or nests of any kind.

If you have a question about tent caterpillars or other gardening topics, contact the UConn Home & Garden Education at (877) 486-6271 or www.homegarden.cahnr,uconn.edu or your local Cooperative Extension Center.