In southern Ontario, boxwood shrubs face significant threats from three major issues: the box tree moth, the boxwood leaf miner, and boxwood blight.
Box Tree Moth
The box tree moth (Cydalima perspectalis) is an invasive species originally from East Asia. The larvae are particularly destructive, feeding on the foliage of boxwood plants, which can lead to significant defoliation and plant death. Adult moths are white with brown borders and lay clusters of eggs on the underside of leaves. The caterpillars, bright green with black heads, spin silk webs that protect them as they feed.
Signs of Infestation:
- Caterpillars that resemble twigs
- Webbing within the shrub
- Feces on leaves
- Discoloration and defoliation
Prevention and Management:
- Regular inspection and early detection are crucial.
- Use Bacillus thuringiensis kurstaki (BTK) insecticide during larval feeding periods for effective control.
- For severe infestations, multiple BTK applications are needed throughout the year.
Boxwood Leaf Miner
The boxwood leaf miner (Monarthropalpus flavus) is another significant pest. The larvae are small maggots that feed between the layers of boxwood leaves, causing blistering and discoloration.
Signs of Infestation:
- Blisters and yellowing on leaves
- Premature leaf drop
Prevention and Management:
- Use systemic insecticides that target leaf miners.
- Regular pruning to remove infested foliage can help manage minor infestations.
Boxwood Blight
Boxwood blight is a fungal disease caused by Calonectria pseudonaviculata. It spreads rapidly in warm, humid conditions and can decimate boxwood plants if not controlled.
Signs of Infestation:
- Dark or light brown leaf spots
- Black streaks on stems
- Rapid defoliation starting from the bottom of the plant
Prevention and Management:
- Avoid overhead watering to reduce humidity.
- Ensure good air circulation around plants.
- Use fungicides as a preventive measure.
- Infected plants should be removed and destroyed to prevent the spread of spores