Invasive Pests and Diseases Threaten Boxwood Shrubs in Ontario

Boxwood shrubs in the GTA and southwestern Ontario are under attack from invasive pests and fungal diseases, causing significant damage. Arborists advise monitoring and proactive measures to detect early signs of infestation and prevent the spread of these destructive threats.

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Nitish Verma
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Invasive Pests and Diseases Threaten Boxwood Shrubs in Ontario

Invasive Pests and Diseases Threaten Boxwood Shrubs in Ontario

Boxwood shrubs in the Greater Toronto Area (GTA) and southwestern Ontario are under siege from a trio of invasive pests and fungal diseases. The box tree moth, boxwood leaf miner, and boxwood blight are causing significant damage and prompting arborists to advise clients to reconsider planting boxwoods.

Why this matters: The spread of invasive pests and diseases can have devastating consequences for ecosystems and economies, and climate change is exacerbating the issue. If left unchecked, these threats can lead to the loss of biodiversity, economic losses for industries reliant on affected plant species, and decreased environmental resilience.

The box tree moth, added to the Canadian Food Inspection Agency's list of regulated pests in 2023, has led to Ontario being declared an infested area. Boxwood leaf miners, small maggots that eat between the layers of leaves, are also causing harm. Additionally, boxwood blight, a fungal disease, can kill boxwood plants if left untreated.

The impact of these pests and diseases can be devastating. "They can kill a hedge within the summer season if they're left untreated, and it's something that we've been noticing right across the city," said Erik Benneter, district manager for west Toronto with Davey Tree Care Services.

Monitoring boxwood shrubs is crucial to detect early signs of infestation, such as moth caterpillars, feces, webbing, and discolored leaves. While there is no preventative option, BTK,a natural insecticide, can be used to minimize damage. For properties with a limited number of boxwood shrubs, removal and replacement with heartier plants like yew bushes, burning bushes, and junipers may be considered.

Climate change is playing a role in the spread of these invasive pests and diseases. Warmer winters and summers are contributing to the problem, as insects are not dying off as much as they used to over winter. The GTA and parts of Ontario are facing an increasing number of invasive pests and fungal diseases affecting various tree and bush species.

Benneter emphasizes the importance of maintaining healthy plants to improve their resilience against pests and diseases. "The healthier the plant is, the better able it is to withstand insects and diseases on its own," he said, highlighting proper fertilizing, mulching, and watering practices.

As the threat of invasive pests and fungal diseases continues to grow in the GTA and southwestern Ontario,vigilant monitoringand proactive measures will be essential to protect boxwood shrubs and other vulnerable plant species. Arborists and property owners must work together to detect early signs of infestation and take appropriate steps to minimize damage and prevent the spread of these destructive pests and diseases.