Maintaining healthy and attractive boxwood shrubs in Massachusetts is important when you want to keep these evergreen favorites looking good in your home landscape.
Part of keeping your boxwoods growing healthy is watching out for some common threats that can cause significant damage if left unchecked, leading to unsightly and weakened plants.
Let’s explore two of those threats: the box tree moth and boxwood blight. We’ll discuss signs and symptoms of these issues and how to control them.
Box Tree Moth
The box tree moth (Cydalima perspectalis) is a relatively new threat to North American boxwoods, having been introduced from Asia.
Native to North China and Korea, box tree moth was first confirmed in July 2021 in the western New York cities of Buffalo and Rochester. It was detected in Massachusetts in August 2023 in Cape Cod.
Life Cycle
Understanding the box tree moth life cycle is crucial for effective pest management.
It starts with the egg stage, when female moths lay clusters of pale, yellow eggs on the undersides of boxwood leaves. The eggs hatch in about three to seven days.
Once those box tree moth eggs hatch, you enter the larval stage, which is this pest’s most destructive. Once they emerge from the eggs, they feed on boxwood leaves and bark, going through several instars in two to four weeks – ideal conditions can shorten this.
During the pupal stage, mature larvae form cocoons among the boxwood foliage and pupate for about two weeks.
Finally, you reach the adult stage, where the moths emerge, mate, and lay eggs, beginning the cycle again. There can be two generations per year (Canada and Buffalo have seen two generations, but Cape Cod hasn’t yet).
Box Tree Moth Damage: Signs & Symptoms
The damage caused by box tree moth larvae can be severe and easily identifiable:
- Leaf Damage: Larvae feed voraciously on boxwood leaves, skeletonizing them and leaving behind only the This can happen in just two weeks.
- Webbing: Infestations are often accompanied by silk webbing and frass (insect droppings) on the foliage.
- Defoliation: Heavy infestations of box tree moth can lead to significant defoliation, weakening the plant and making it susceptible to other stresses. They also can girdle the stems, which can quickly kill the plant. Unfortunately, evergreens that lose too many leaves can die.
As its name suggests, the primary hosts of these pests are boxwood species (Buxus spp.)There have been isolated reports of feeding on burning bush (Euonymus alatus), Japanese spindletree (E. japonicus), purple holly (Ilex chinensis), and orange jessamine (Murraya paniculata), but box tree moth is unlikely to be a pest on these species.
Box Tree Moth Control
Effective box tree moth control requires a combination of monitoring, cultural practices, and treatments:
- Monitoring: Regularly inspect boxwoods for signs of eggs, larvae, and damage. Pheromone traps can help monitor adult moth activity. How does box tree moth spread? Long distance spreading has been through the shipment of infested plant material that may arrive in your area or that you may pick up and plant. Adult moths can also fly up to 6 miles and infest new plantings. This is why regular monitoring is important. Box tree moth reporting can be done by alerting your local arborist if you see any of these pests. This is essential to help stop the spread. Regulatory agencies have imposed quarantines on boxwood to prevent the spread of the insect, so it’s important to be familiar with regulations in your area before moving boxwood plants.
- Cultural Practices: Maintain plant health through proper watering, fertilization, and pruning. Remove and destroy infested plant material to reduce larval populations. Also, never buy boxwoods from quarantine areas.
- Biological Control: Natural predators like birds and parasitic wasps can help control box tree moth populations.
- Other Control Strategies: Insecticides can be effective, particularly those targeting larvae. Massachusetts certified arborists will ensure thorough coverage of the foliage, following label instructions.
Post Damage Care
If your boxwoods have suffered from box tree moth damage, follow these steps for recovery:
- Pruning: Remove damaged and infested branches to stimulate new growth and reduce pest habitat.
- Fertilization: Apply a balanced fertilizer to support recovery and regrowth.
- Watering: Ensure consistent watering to help stressed plants recover, but avoid waterlogging.
- Mulching: Apply mulch to conserve moisture and regulate soil temperature, promoting healthy root growth.
- Consider replacing your box woods with more box wood moth-resistant species.
Boxwood Blight
What is boxwood blight? Boxwood blight, caused by the fungal pathogens Calonectria pseudonaviculata and Calonectria henricotiae, is a serious disease affecting boxwoods. It spreads rapidly and can cause significant defoliation and dieback.
What causes boxwood blight? Warmth and humidity spread the fungus, as well as the following:
- Infected Plant Material: Introduction of infected plants or cuttings.
- Water Splash: Spores can be spread by rain or irrigation.
- Tools and Equipment: Contaminated pruning tools and equipment can transfer spores.
- Humans and Animals: Movement through infested areas can spread the spores.
Boxwood Blight Damage: Signs & Symptoms
What does boxwood blight look like? Initially, you might see light or dark brown leaf spots – many times with dark borders. Then those Infected plant leaves can turn yellow or brown and quickly drop from the plant. On plant stems, you may see black, diamond-shaped lesions.
Recognizing these boxwood blight disease signs is essential for early intervention:
- Leaf Spots: Circular, dark brown to black spots on leaves, often with a tan center.
- Stem Lesions: Dark streaks or lesions on stems.
- Defoliation: Rapid leaf drop, starting from the bottom of the plant and moving upward.
- Dieback: Severe cases result in dieback of branches and stems.
Boxwood blight infects all boxwood species – the most susceptible hosts are English, American and Korean boxwoods. Boxwood blight can be confused with less serious diseases such as Volutella blight, so it’s important to consult with an arborist to confirm the diagnosis.
How To Treat Boxwood Blight
Treatment of boxwood blight involves cultural practices, sanitation, and fungicide applications:
Start with good cultural practices, such as ensuring good air circulation around plants by spacing them appropriately. Avoid overhead watering. This helps prevent the disease.
There are no curative products available currently to control boxwood blight. But a licensed arborist can apply fungicides as a preventive measure during periods of high humidity and rainfall to protect boxwoods that are susceptible or near other infected plants.
Can Boxwoods With Blight Be Saved?
There is no cure for boxwood blight, but you can try these steps to save infected plants and prevent the spread of the disease:
- Remove and destroy infected plant material. Sanitize tools and equipment after use with a disinfectant such as a dilute bleach solution or rubbing alcohol.
- Since boxwood blight can live in the soil for up to six years, avoid planting susceptible boxwoods in that area for that period of time.
- Properly prune boxwoods by making good cuts and not leaving them open to winter damage and stress by cutting them too severely.
At Hartney Greymont, we have local arborists throughout Massachusetts located in Needham, Concord, Danvers, Cape Cod, and the surrounding areas to monitor the health of your trees for early signs of insect and disease problems.
Contact Hartney For Your Local Landscape Needs In Massachusetts.
