Boxwood leaf-eating caterpillar (Monarthropalpus flavus) is quite common on cultivated boxwood shrubs. This is one of the worst types boxwood pestsBut some plant varieties are more susceptible than others. Severe infection, if left unchecked, will eventually kill the plant within about a year.
However, with the right treatment, you can save your hedge. Boxwood leafminers are the larval form of a type of fly. They damage a wide variety of plants, including many vegetables and ornamentals like boxwood. Here’s how to identify, remove, and prevent boxwood leafminers.
Does your plant have boxwood leafminers?
To determine if you have leafminers on your boxwood, you need to understand the life cycle of the boxwood leafminer. The life cycle begins in the spring when females lay their eggs directly on the underside of the boxwood leaves. This is in contrast to other leafminers, which lay their eggs on the surface.
When the larvae hatch, they begin to eat the leaves from the inside, causing the characteristic boxwood leaf-eating damage. The larvae pupate in the winter and hibernate inside the leaf tissue. They emerge as adults in the spring.
Boxwood leafhoppers are small flies that resemble midges. Their bodies are red or orange-yellow in color. They can sometimes be seen flying around boxwood plants. The larvae are green or whitish-yellow and are only about 3mm long.
The initial signs of a boxwood leaf borer infestation are pale green or yellow spots on the upper surface of leaves. As the infestation continues, it causes the following additional signs:
- Wrinkled, yellow or brown blisters on the underside of leaves.
- There is a slight raised part on the upper leaf surface.
- The structure and shape of the leaves are deformed due to blistering.
- Transparent round spots.
- The leaves turn brown.
- Fallen leaves.
(Image source: Qwart / Getty Images)
How to get rid of boxwood leaf miners
Prevention is best, but if you do have leaf miners, treat the infestation as soon as possible. If you spot the telltale signs of leaf miners while the larvae are still in the leaves, remove the stems and dispose of them safely. If you are certain you have seen leaf miners on your boxwood leaves, it is best to remove and destroy them.
The best time to control with chemicals is when the adults emerge from the leaves in early spring. You can try products containing bifenthrin, carbaryl, cyfluthrin, or malathion. These foliar products will not kill the larvae inside the leaves, but systemic insecticides such as imidacloprid are often effective.
When considering a treatment for boxwood leafminer, it is important to weigh the pros and cons. In some cases, these chemical controls can be extremely toxic to bees and other pollinators. Therefore, use chemical controls with caution and follow instructions carefully.
Unfortunately, organic pesticides Oils like neem are not very effective against boxwood leafminers. However, some experts believe that natural predators like the green lacewing, if introduced into your yard, could curb infestations.
How to prevent boxwood leaf borer
Basically, boxwood care and keeping plants healthy and growing is the best prevention. Healthy plants are less susceptible to pests and diseases. Water and drain plants well, boxwood pruning regularly and provide proper fertilizer.
Another good way to prevent this problem is to start with boxwood varieties that are less susceptible to leafminers. For Buxus microphyllaChoose Japonica, Green Pillow or Franklin’s Gem. Good choices for Buxus sempervirens including Argenteo-variegata, Pendula, Suffruticosa and Vardar Valley. You may also consider planting alternatives to boxwood in your garden or yard.
(Image source: Tetiana Mykytiuk / Getty Images)
Is the boxwood leafminer the most dangerous?
Chemical treatments for boxwood leaf miners can be effective. If left untreated, the infestation can become severe and life-threatening. The larvae eventually cause so much damage to the leaves that the plant cannot survive.
A boxwood that has been completely browned by leafminers will probably not recover. If you can remove the most damaged branches and apply chemical control, the tree may recover the following year. Again, check product instructions carefully and be aware that some chemicals can be toxic to pollinators.
If you are not confident in your ability to handle the infestation or want a professional opinion on whether the boxwood can be saved, contact a certified arborist or local extension service agent.
Note: Any recommendations regarding the use of chemicals are for informational purposes only. Chemical control should only be used as a last resort, as organic methods are safer and more environmentally friendly.
