After just a few years providing boxwood treatments, I am second guessing ever planting my once favourite shrub. I personally love boxwoods. They work both as a main feature or shrub to complement the rest of the landscape. Boxwoods (Buxus) are one of the most versatile shrubs and are heavily planted in residential landscapes. Of interest, boxwoods can be trained to take almost any desired shape. Unfortunately, in recent years boxwoods have not been known for the following, but for its recurring problems we are still seeing today.
Boxwood Leafminer
From Oakville to Niagara on the Lake, and everywhere in between along the Golden Horseshoe, boxwood leafminers are the most common damaging insect we see on the shrub. Damage first presents when the boxwood’s beautiful deep green turns a discolored light yellowish brown. The leafminer will cause blisters on the foliage and eventually, defoliation.
First sighting of the boxwood leafminer is between April and May, depending on the weather. The adult leafminer will emerge. Looking similar to a mosquito, the adult leafminer is a small fly with an orange tanned colour. Usually living up to 2 weeks, the adults will mate and the females will lay their eggs in the underside of the new growth of the boxwood.
Eggs hatch in early Summer, where the larvae will stay, feeding on the inside of the plant’s foliage. Having a 9-10 month cycle, they will remain in the foliage until the following Spring when they emerge as adults and begin a new cycle.
Other common issues we diagnose are box tree moth, psyllids, scale and spider mites.
Treatments for boxwood leafminers
Treatments in Ontario are limited due to restrictions on systemic injection options, leaving foliar applications. These treatments are effective, but require perfect timing to successfully control and suppress leafminer populations.
Early spring pruning is recommended to remove some of the affected growth before adults emerge and repeat another cycle.
Ensuring your boxwoods have appropriate amounts of water and good quality soil will help with the damage caused by the boxwood leafminer. The better the growing condition, the higher chance a shrub has to overcome an infestation.
Another good practice is to do your research before buying your boxwoods. Some cultivars are more genetically resistant to boxwood leafminers than others.
As wonderful as they look, when they look their best, it can be an endless headache when problems occur. Do your research and understand the potential risk and maintenance when adding any tree or shrub into your landscape.