Monarthropalpus flavus
The Boxwood Leafminer (Monarthropalpus flavus) is a significant pest of boxwood plants (Buxus spp.). This insect is a species of gall midge and is considered the most serious insect pest that attacks boxwoods.
Boxwood Leafminer primarily targets species of boxwood plants. These evergreen shrubs are known for their dense, attractive foliage and are commonly used in landscaping and horticulture.
While all boxwood species can be affected by the leafminer, certain varieties may show varying levels of susceptibility. Boxwood Leafminer heavily attacks common boxwood (Buxus sempervirens), round leaf boxwood, Buxus roduntifolia, and balearica boxwood (Buxus balearica).
The Boxwood Leafminer is native to Europe but has become established in many regions across the globe where boxwoods are grown. In the United States, it is widespread from coast to coast, where it can cause significant damage to boxwood shrubs.
The Boxwood Leafminer has a complete metamorphosis life cycle, including egg, larval, pupal, and adult stages. This cycle takes one year to complete.
The life cycle of the Boxwood Leafminer is synchronized with the growth of its boxwood host, and the timing can vary depending on the local climate and the specific variety of boxwood. Regular monitoring of boxwoods can help detect the presence of leafminers, and timely intervention can prevent significant damage.
Boxwood Leafminers cause significant damage to boxwood plants during their larval stage when they feed on the leaves from the inside, creating visible blisters or mines.
Damage: The feeding damage appears as blisters on the undersides of the leaves. As the larvae continue to feed, these blisters can become more pronounced and may turn yellow or brown. In severe infestations, this can lead to premature leaf drop and overall reduction in plant health. The continuous stress can make the boxwood more susceptible to other diseases or pests. In extreme cases, entire plants can be defoliated.
Detection: The blisters on the leaves are the most obvious signs of a Boxwood Leafminer infestation. These blisters are typically more noticeable on the underside of the leaves. If you hold an infested leaf up to the light, you may see the larva moving inside the blister. Adult flies are another sign of infestation, although they are only present for a short period in the spring.
It’s worth noting that some varieties of boxwood may show more significant symptoms of leafminer damage, while others may appear to be more resistant.
Preventing and controlling Boxwood Leafminer infestations can involve several strategies, including cultural practices, biological controls, and chemical treatments.
Buxus microphylla var. japonica: Often called Japanese Boxwood, this variety is more heat-tolerant than some other types of boxwood and generally grows in a rounded shape. It can reach up to 6 feet in height and spread, but it grows relatively slowly and can be kept smaller with pruning.
Buxus microphylla ‘Green Pillow’: This is a low-growing, compact boxwood that typically reaches only about 1 foot in height but spreads up to 3 feet wide. Its common name comes from its soft, rounded shape that resembles a green pillow.
Buxus microphylla ‘Grace Hendrick Phillips’: Known for its small, densely packed leaves, this variety grows in a rounded form and can reach up to 3 feet in height and width. It’s often used for low hedges or as a border plant.
Buxus microphylla var. sinica ‘Franklin’s Gem’: A compact and rounded shrub, ‘Franklin’s Gem’ has a mature height of around 1-2 feet. It’s known for its small, bright green leaves and good winter hardiness.
Buxus sempervirens ‘Pendula’: Also known as Weeping Boxwood, ‘Pendula’ has a unique cascading growth habit with long, arching branches. It’s a larger variety that can reach up to 5 feet in height.
Buxus sempervirens ‘Argenteo-varigata’: This variety features dark green leaves with creamy white edges, adding a pop of color to landscapes. It can grow up to 5 feet tall and wide.
Buxus sempervirens ‘Handworthiensis’: This variety is characterized by its narrow, columnar growth habit. It can reach up to 6 feet in height but stays relatively narrow, often used for hedging or topiaries.
Buxus sempervirens ‘Pyramidalis’: As its name suggests, ‘Pyramidalis’ grows in a natural pyramid shape. It’s a larger variety, reaching up to 15 feet in height.
Buxus sempervirens ‘Suffruticosa’: Also known as English Boxwood, this is a slow-growing dwarf variety with dense foliage, often used for low hedges or edging.
Buxus sempervirens ‘Vardar Valley’: Known for its resistance to winter bronzing, ‘Vardar Valley’ has a spreading habit and grows up to 2-3 feet in height and 4-5 feet wide.
Buxus sempervirens ‘Justin Brouwers’: A compact variety with a naturally rounded shape, ‘Justin Brouwers’ has small, dark green leaves and grows up to 2 feet (60 cm) in height and width.
Buxus harlandi ‘Richard’: This variety is characterized by its long, glossy leaves and distinctively textured bark. It’s more heat- and drought-tolerant than many other boxwoods and can grow up to 4-6 feet tall.
Buxus sinica var. insularis ‘Nana’: A slow-growing dwarf variety, ‘Nana’ is known for its small, shiny leaves and compact habit. It typically grows only about 1-2 feet (30-60 cm) tall.
Several natural enemies of the Boxwood Leafminer have been identified, including green lacewings and spiders. Encouraging these beneficial insects in your garden can help control leafminer populations.
Insecticides can be used to control leafminer infestations, but timing is important. Ideally, insecticides should be applied just after the adult flies emerge and before they lay their eggs. Consult with a local extension service or a professional to identify the most effective and environmentally friendly options for your area.
Remember, always follow all label directions when using any pesticide, and consult with a local professional or your local extension service for the best advice on managing pests in your particular situation.
In all cases, regular monitoring of boxwoods is critical to catch any infestation early and manage it effectively before it can cause significant damage.
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Becoming a contributing member of Gardenia is easy and can be done in just a few minutes. If you provide us with your name, email address and the payment of a modest $25 annual membership fee, you will become a full member, enabling you to design and save up to 25 of your garden design ideas.
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