Monarthropalpus buxi The boxwood leaf miner is one of the most serious pests of boxwood. The larvae spend the winter in the leaf. When the weather warms in spring, they feed on the tissue between the leaf surfaces. In late April or May a tiny (1/10-inch), gnatlike, orange fly emerges from the pupal case inside the leaf. The emerging flies swarm around the plant in early morning, mating and laying eggs in the leaves. New blisters develop in midsummer from feeding by this next generation of larvae. When the weather turns cold, the larvae become inactive until the following spring.
Apply an insecticide labeled for boxwood leaf miners, following label directions. Plant resistant varieties if possible.
Psylla buxi The boxwood psyllid is prevalent in temperate regions of the country where boxwood is grown. American boxwood is more severely attacked than English boxwood. The immature psyllid feeds by sucking the juices from growing leaves, resulting in the yellowing and cupping. As it feeds, it secretes a white, waxy material that protects it from parasites and chemical sprays. The insect is unable to digest all the sugar in the juices, and it excretes the excess as honeydew, a sticky substance that covers the leaves. A black sooty mold often grows on the honeydew. The insect matures in early summer, and the female fly lays her eggs in the base of buds in the fall, where they remain until the following spring.
Apply insecticidal soap or an insecticide labeled for boxwood psyllids.
Nematodes are microscopic worms that live in the soil. They feed on plant roots, damaging and stunting them. The damaged roots can''t supply sufficient water and nutrients to the aboveground plant parts, and the plant is stunted or slowly dies. Nematodes prefer moist, sandy loam soils. They can move only a few inches each year on their own, but they may be carried long distances by soil, water, tools, or infested plants. Testing roots and soil is the only positive method for confirming the presence of nematodes. Contact your local county extension office for sampling instructions and addresses of testing laboratories. Root rots and soil problems such as poor soil structure, drought stress, nutrient deficiency can also produce symptoms similar to those caused by nematodes. These problems should be eliminated as causes before root and soil samples are sent for testing.
Properly watered and fed plants can tolerate some nematode feeding. If replanting, consider a shrub that is resistant to nematodes.
This plant disease is caused by a soil-inhabiting fungus (Phytophthora) that attacks more than one hundred kinds of ornamental plants. The fungus is carried in infected plants, infested soil, or soil water. It enters the roots and works its way up the plant, blocking the upward flow of water and nutrients. Plants in overwatered or poorly drained soils are more susceptible to attack.
Once the fungus becomes established in the soil, it will remain indefinitely. Avoid overwatering. Remove severely diseased and dying trees. Do not replant susceptible plants in the same area.
These mites, related to spiders, are major pests of many garden plants. They cause damage by sucking sap from the undersides of leaves. As a result of their feeding, the plant''s green leaf pigment disappears, producing the stippled appearance. Spider mite webbing traps cast-off skins and debris, making the plant messy. Mites that infest boxwood are most prolific in cooler weather. They are most active in the spring and occasionally in the fall. By the onset of hot weather (70°F and up), the mites have caused their maximum damage.
Apply an insecticide labeled for this pest, following label directions. Hose down plants with a high-pressure nozzle every few days to knock off webs and mites.
Boxwood is severely damaged by cold, drying winter winds, especially if temperatures are below freezing and the weather is clear. The leaves lose their moisture more rapidly than it can be replaced by the root system. Cells in the leaf dry out and die. This condition is most pronounced when water is unavailable because the soil is frozen. Leaves, along with twigs and branches, also die during early fall or late spring freezes, when the plant is growing. Young succulent growth cannot withstand the cold temperatures.
Boxwood is severely damaged by cold, drying winter winds, especially if temperatures are below freezing. Provide shelter and windbreaks for plants growing in cold regions. Don''t fertilize or prune in the fall. Water in late fall or winter, to keep the soil moist. Mulch plants after they become dormant.