Boxwood Problems?

Things to watch out for with Boxwoods

With environmental factors happening more and more there are a few problematic things now affecting boxwoods. These include the new invasive Box Tree Moth, Boxwood Blight, and Boxwood Leaf Miner. If left untreated these problems can severely damage and kill off boxwoods.

Box Tree Moth

Box tree moths cause significant damage to boxwoods through leaf feeding, leading to defoliation, weakening, and potentially plant death. Caterpillars of the moths consume leaves, leaving skeletonized foliage.

Visible Signs of Infestation:

Chewed leaves- Look for missing sections of leaves, particularly on the edges, as well skeletonized leaves where only the veins remain.
Larvae- Green caterpillars with black heads are a clear sign of box tree moth infestations. These caterpillars can be found hiding in webbing or among twigs and leaves.
Webbing- The larvae create webs in and around infested plants.
Frass (sawdust-like debris)- Look for small, dark pellets of frass, which are the larvae’s excrement.
Pupae- You may also find pupae, which are silken cocoons, amongst the webbing and damaged leaves.
Adult Moths- While adult moths are nocturnal and harden to spot, they are generally white with a brown border.

Prevention and Management:

Biological Control- Use a biological pesticide containing Bacillus thuringiensis (BTK). BTK is a naturally occurring bacteria that is safe to humans and pets. Apply BTK spray when larvae are actively feeding on boxwood plants. Multiple applications may be necessary to effectively control the larvae.
Monitoring & Reapplication- Regularly monitor boxwoods for caterpillars and feeding damage. Re-inspect plants 5-7 days after applying BTK to ensure its effectiveness. If larvae are still present apply another application of BTK.

Fertilizing & Pruning:

Fertilize boxwoods in early June and mid-July to help them recover from damage.
Treat boxwoods with Restore & Protect or Turbo Grow.
Prune plants in late winter, early spring.
Dispose of infested boxwoods or clippings properly to prevent the spread of the pest.

Boxwood Blight

This is a serious fungal disease that leads to defoliation, starting with the lower branches, and can ultimately kill the entire plant. The disease is characterized by leaf spots, stem cankers, and rapid defoliation, often starting at the base of the plant.

Symptoms:

Leaf Spots- Small brown to black spots appear on the leaves, which can enlarge and cause entire leaves to turn brown, shrivel and fall off.
Stem Cankers- Dark brown to black streaks develop on green stems.
Defoliation- The plant rapidly loses leaves, starting at the lower branches and moving upwards.
Straw-Colored Patches- Boxwoods may develop unsightly straw-colored bare patches.

Causes and Spread:

Fungal Pathogen- The disease is caused by the fungus Calonectria pseudonaviculata.
Moisture- Warm and humid conditions, especially after rainfall, favor the spread of the disease.
Spores- The fungus produces spores that can be spread via splashing rain, irrigation tools, clothing, and leaf blowers.
Soil- The pathogen can persist in the soil for several years, potentially infecting new plants.

Prevention and Management:

Sanitation- Remove and dispose of the infected plant material properly (burning, bagging for the landfill, NEVER in your compost).
Pruning- Prune infected branches and sanitize tools with a 10% bleach solution or 70% rubbing alcohol.
Airflow & Sunlight- Prune dense shrubs to improve air circulation and sunlight penetration, which can help keep foliage dry.
Mulch- Use bark mulch, avoiding horticultural fabric, to help retain moisture and promote root growth.
Fungicides- Certain fungicides may help control the disease if applied proactively.

Boxwood Leaf Miner

Boxwood Leaf Miners are a significant pest that can damage boxwood plants, causing blisters, discoloration, and potential defoliation. They are tiny, orange, gnat-like flies that spend their larval stage feeding inside the boxwood leaves.

Life Cycle & Damage:

Adults- Small, orange flies emerge in early spring.
Eggs- Females lay eggs on the underside of the new boxwood growth.
Larvae- The larvae, which are small, yellow-orangish maggots, feed inside the leaves, creating visible blisters or mines.
Pupation- Larvae pupate inside the leaves and emerge as adult flies the following spring.
Damage- The larvae’s feeding activity can cause leaves to blister, turn yellow or brown, and eventually drop.
Severe Cases- In severe infestations, boxwoods can experience significant defoliation, potentially leading to plant death.

Control & Prevention:

Early Detection- Regularly inspect boxwoods for signs of leafminer damage, such as blisters or discolored leaves.
Pruning & Removal- Prune or remove affected leaves to reduce insect population.
Systemic Insecticides- Systemic insecticides can be used to control leafminer larvae, you would have to call a landscaper with a Pesticide Applicators Licence to spray and treat your affected boxwoods.
Foliar Sprays- Insecticidal sprays can be applied to control adult flies, but repeated applications may be needed.
Timing of Control- Control measures are most effective when applied at the corrext stage of leafminer life cycle, such as after egg hatching.