Boxwoods are a beloved staple in many Southern Ontario landscapes, prized for their evergreen foliage and formal shapes. However, these beautiful shrubs can be susceptible to various pests that can compromise their health and appearance. At The Spider Guys, we understand the importance of maintaining a vibrant landscape, so we’ve compiled this guide to help you identify and manage common boxwood pests in our region.
The Prime Suspect: The Box Tree Moth
The Box Tree Moth (Cydalima perspectalis) is a relatively new and highly destructive invasive pest that has become a significant concern for boxwood owners in Southern Ontario. Early detection and swift action are crucial to protect your plants.
How to Know You Have Box Tree Moth:
Sudden and Rapid Defoliation: This is often the most alarming sign. Your once lush boxwood may quickly appear sparse or even completely stripped of its leaves.
Webbing: Look for silken threads spun around leaves and branches, often accompanied by small, green or yellowish-green pellets (frass – caterpillar droppings).
Green Caterpillars: Closer inspection will reveal the caterpillars themselves.
What the Box Tree Moth Looks Like and Its Lifecycle:
Eggs: Small, flat, pale yellow, and laid in overlapping clusters on the underside of leaves.
Larvae (Caterpillars): Young larvae are small and light green. Mature larvae can reach up to 4 cm in length, with a bright green body, black and white stripes, and black spots.
Pupae: Brownish-green pupae are usually found within silken cocoons amongst the leaves and twigs.
Adult Moths: Distinctive white moths with a brown border along the wingspan (though some can be entirely brown). They are nocturnal and you might see them fluttering around your boxwoods, especially in the evening. The moth typically goes through 2-3 generations per year in our climate, meaning multiple periods of active feeding.
Damage Caused by Box Tree Moth:
The larvae are voracious eaters, feeding primarily on the leaves. In heavy infestations, they can strip the entire plant, leaving behind only bare twigs. Repeated defoliation weakens the plant, making it susceptible to other stresses and potentially leading to its death.
DIY Treatments for Box Tree Moth:
Handpicking: For small infestations, you can physically remove and destroy eggs, larvae, and pupae. Regularly inspect your plants, especially the undersides of leaves and inner parts of the shrub.
Bacillus thuringiensis kurstaki (BtK): This is a biological insecticide effective against young caterpillars. Apply it thoroughly to all leaf surfaces, following the product instructions. Repeat applications may be necessary due to the multiple generations of the moth.
Pheromone Traps: These traps attract and capture adult male moths, helping to monitor their presence and potentially reduce mating. However, they are generally more effective for monitoring than for complete control of a heavy infestation.
When to Call the Professionals for Box Tree Moth:
Large or Established Infestations: If the infestation is widespread or you are seeing significant defoliation, professional intervention is recommended. We have access to more potent and targeted insecticide treatments and can develop a comprehensive management plan.
Difficulty Reaching Infested Areas: Dense or large boxwoods can make thorough DIY treatments challenging. Our trained technicians have the equipment and expertise to reach all parts of the plant.
Repeated Infestations: If you have tried DIY methods and continue to experience infestations, professional help can identify underlying issues and implement more effective long-term strategies.
Other Common Boxwood Pests in Southern Ontario:
While the Box Tree Moth demands immediate attention, other pests can also affect your boxwoods.
1. Boxwood Leafminer:
How to Know You Have It: Blister-like swellings or raised areas on the lower surface of the leaves. Affected leaves may appear yellowish or brown.
What it Looks Like: Tiny, yellowish maggots feeding inside the leaves. The adult is a small, orange-yellow fly that emerges in spring.
Damage: Unsightly foliage, potential for leaf drop in severe infestations, but generally doesn’t kill the plant.
DIY Treatments: Pruning and destroying infested leaves in late winter before adult emergence can help. Horticultural oil applied at the correct time can also be effective against the larvae.
When to Call Professionals: For heavy infestations where aesthetic damage is significant or if you prefer systemic insecticide treatments applied by licensed technicians for more thorough control.
2. Boxwood Psyllid:
How to Know You Have It: Cupped or distorted new growth at the tips of branches. You might see a white, waxy residue inside the cupped leaves.
What it Looks Like: Small, pale green, aphid-like insects (nymphs) covered in a white, waxy substance. The adults are small, jumping insects.
Damage: Primarily aesthetic, causing distorted foliage. Heavy infestations can stunt new growth.
DIY Treatments: Pruning affected tips can remove many of the psyllids. A strong spray of water can also dislodge them. Insecticidal soap or horticultural oil can be effective when applied thoroughly.
When to Call Professionals: If the infestation is widespread and affecting a large portion of your boxwoods, or if you are concerned about the aesthetic impact and DIY methods haven’t provided sufficient control.
3. Boxwood Spider Mites:
How to Know You Have It: Leaves appear stippled or speckled with tiny yellow or bronze dots. In severe infestations, you might see fine webbing on the undersides of leaves. The overall plant may look dull or dusty.
What it Looks Like: Very tiny (barely visible) spider-like creatures, usually found on the undersides of leaves.
Damage: Chlorosis (loss of green color), leaf drop, and reduced plant vigor in heavy infestations.
DIY Treatments: A strong jet of water can dislodge mites. Horticultural oil or insecticidal soap can also be effective, but multiple applications may be needed. Ensure thorough coverage of the undersides of leaves.
When to Call Professionals: For persistent infestations that are causing significant damage, or if you prefer professional miticide applications for more rapid and comprehensive control.
Protecting Your Boxwoods is Our Priority
At The Spider Guys, we are committed to helping you keep your Southern Ontario landscape healthy and beautiful. If you suspect a pest infestation on your boxwoods, don’t hesitate to contact us for expert identification and effective management solutions. We have the knowledge, experience, and tools to protect your valuable plants. Call us today for a consultation!