Volume 5 No.3 May 8, 1998
Boxwood is a favorite landscape plant but several important insect pests plague it. The three major pests of boxwood include the boxwood leafminer, the boxwood mite and the boxwood psyllid. If you are planting new boxwoods, select varieties which are insect and mite resistant.
Boxwood Leafminer (Monarthropalpus buxi) (94)—This insect is now considered by many to be the most serious insect pest of boxwood. The larvae of this pest can cause extensive damage. Injury is caused when the larvae feed between the upper and lower layers of leaves. Damaged leaves appear blistered and often discolored. Mined or blistered leaves are evident from midsummer until the leaves are shed from the plant.
The boxwood leafminer overwinters as a small (1/8 inch long), yellow-orange larva in evergreen boxwood leaves. It resumes feeding in the early spring, and a short time later, the larva develops into a pupa. Fully developed pupae hang down outside of the leaf. The adults emerge as small, orange gnat like flies in early May at about the time that weigela bloom. They emerge over a two-week period in the spring after the boxwoods have put out their new growth. After laying eggs in the tender leaf tissue the flies die. There is one generation per year. New leaves do not show signs of mining until late summer when larvae are larger.
American boxwood is most commonly attacked, but English and Japanese boxwoods are also susceptible. European boxwood is less susceptible. If you want to plant varieties of English boxwood (Buxus sempervirens) choose varieties such as `Suffruticosa', `Pendula', and `Argenteo-variegata' which are reported to be seldom damaged.
Management options include abamectin, bifenthrin, carbaryl, chlorpyrifos, diazinon, dimethoate, imidacloprid, malathion, permethrin, or trichlorfon. A treatment should be made in the first two weeks of June (448-700 GDD50). Be sure to treat the undersides of the foliage.
Boxwood Mite (Eurytetranychus buxi) (229)—This spider mite feeds on the undersides of leaves and is difficult to see even with a hand lens. Infested leaves appear to be pin-pricked or scratched with tiny white or yellow marks.
Boxwood mites overwinter as eggs on the undersides of leaves. These eggs are round, greenish and flat-topped. They hatch in May and complete a generation in 2 to 3 weeks. Several generations occur each year. Therefore, it is important to apply control measures early in the season. This mite is more active in the spring and early summer. Adult mites are greenish brown. They may be found on the upper or lower surface of leaves. Heavy infestations may result in defoliation. Mite infestations are often worse during dry, dusty conditions.
The boxwood mite is a pest of both European and American boxwood varieties. Japanese boxwood is less susceptible.
You may try washing mites from the foliage with a stream of water. Avoid high nitrogen fertilizers. Treat with abamectin, bifenthrin, dimethoate, fluvalinate, insecticidal soap, horticultural oil, malathion, or oxythioquinox in first 2 weeks in May (245-600 GDD50).
Boxwood Psyllid (Psylla buxi) (137)—The nymphs of this psyllid feed on newly expanding leaves of boxwood and are found on the insides of the cupped terminal leaves. Their feeding causes the leaves to cup upward and become stunted. These symptoms may remain for approximately two years.
The eggs are orange and spindle-shaped and are usually found under bud scales; they are the overwintering stage for this insect. Eggs hatch around the time of budbreak of the host. The nymphs are green and flattened with fluffy white wax on the posterior. The adults are light green, 1/8 inch long and can be found jumping among the foliage. For that reason, adults are commonly known as jumping plant lice. The adults appear by early summer and mate, and the female lays its eggs. There is one generation per year.
Boxwood psyllids attack most American boxwood cultivars and are less severe on English boxwood.
Pesticides usage may be timed for the emergence of adult to prevent egg laying. Chemicals for control of intolerable populations include insecticidal soap, carbaryl, or chlorpyrifos. Make applications in late May (290-440 GDD50).
For subscription information Click Here
Return to Branching Out Home
Page