Identification and Elimination of Boxwood Leafminer: A Boxwood-infesting Pest
The boxwood leafminer (Monarthropalpus flavus), a common pest on cultivated boxwood shrubs, can cause significant damage to these plants. If left unchecked, a severe infestation can kill the plant within a year. However, there are effective solutions for controlling this pest, including organic options.
Organic pesticides, particularly those containing spinosad, a natural insecticide derived from a soil bacterium, can be effective in controlling boxwood leafminers. Spinosad works by disrupting the insect's nervous system, causing feeding to stop and death within 24–48 hours. It is OMRI-listed for organic gardening and is considered relatively safe for people, pets, and beneficial insects when used correctly.
While no direct source specifically discusses boxwood leafminers with organic pesticides explicitly, the principles and examples regarding leafminers and spinosad suggest that organic management is a viable and effective option. Regular monitoring and cultural practices such as mulching and appropriate watering can further support plant health and resilience against leafminer damage.
In addition to organic pesticides, non-chemical approaches such as encouraging beneficial parasitic wasps and removing affected leaves can also help manage leafminer populations by interrupting their lifecycle. Integrated Pest Management (IPM) principles recommend combining such biological controls with selective, reduced pesticide use for the best results.
Prevention is always better than cure. Caring for boxwood and keeping plants healthy is the best prevention against boxwood leafminer. Regular pruning, good irrigation and drainage, and appropriate fertilizer can help keep boxwood healthy. Choosing boxwood cultivars that are less susceptible to leafminers can also help prevent infestations. For example, Japonica, Green Pillow, or Franklin's Gem for Buxus microphylla, and Argenteo-variegata, Pendula, Suffruticosa and Vardar Valley for Buxus sempervirens are less susceptible to leafminers.
If an infestation occurs, treat it as early as possible. To treat a boxwood leafminer infestation, remove branches with signs of infestation and dispose of them safely as early as possible. Products with bifenthrin, carbaryl, cyfluthrin or malathion can be used for chemical control, but they will not kill larvae inside the leaves.
If you are not confident in managing the infestation, contact a certified arborist or your local extension service agent. The boxwood leafminer life cycle begins in spring when females insert eggs directly into the boxwood leaves from the undersides. Early signs of a boxwood leafminer infestation include light green or yellow spots on the upper sides of leaves.
The boxwood leafminer fly is a small gnat-like fly, with a red or orange-yellow body. As the infestation continues, it causes crinkled, yellow, or brown blisters on the undersides of leaves, slight elevations on the upper leaf surfaces, distorted leaf structure and shape, transparent circular spots, leaf browning, and leaf drop.
Natural predators such as green lacewing, if introduced in your yard, could potentially curb boxwood leafminer infestations. Regular monitoring and prompt action can help keep the infestation under control and protect your boxwood shrubs.
Organic pesticides containing spinosad, used in home-and-garden settings for gardening, can be beneficial in controlling boxwood leafminers by disrupting their nervous system and causing death within a day or two. A proactive lifestyle that prioritizes plant health through regular monitoring, cultural practices like mulching and appropriate watering, and choosing less susceptible boxwood cultivars can help deter boxwood leafminer infestations.
