Boxwood psyllid (Monarthropalpus flavus) are small, soft bodied insects that feed on the sap of boxwood. They are light green in colour and the nymphs are covered in whitish waxy secretions. These waxy secretions can make the boxwood appear to have dandruff. The nymphs feeding causes the leaves to curl over and cup; enclosing them in a protective shield safe from predators, weather and garden sprays. Although the feeding damage is considered cosmetic and not a real threat to the plants life, it none-the-less can really mar the appearance.
Boxwood Psyllid Damage
As already mentioned the boxwood can appear to be covered in dandruff. The terminal tips of the young new growth becomes cupped soon after the boxwood has put on it’s new growth. The leaves affected by this cupping will die in about a year and new growth will in the area will be affected for 2 years after. Black sooty mold can also develop on leaves, the result the of honeydew excreted by the larvae.
Boxwood Psyllid Life Cycle
Adult boxwood psyllid lay their orange coloured eggs in the bud scales of boxwood in June and July. The following April to May, just as the boxwood begin putting on their new growth, the eggs hatch and the light green nymphs begin feeding on the buds and young leaves. The nymphs secrete a waxy filamentous substance called ‘lerp’ which they use to partially cover themselves in for protection. The nymphs quickly go through 5 instar stages before maturing to an adult in late May to early June. The adults are light green in colour and measure about 1 1/2 mm (1/16″). They have clear wings and are good jumpers. When the boxwood is disturbed they fly up. Boxwood psyllids have one generation per year.
Boxwood Psyllid Management and Control
Boxwood psyllid can be a challenging insect to control but thankfully their damage is more cosmetic then life threatening.
Cultural practices: prune out the cupped leaves before the nymphs become adults. This will help to reduce their populations. Be sure to cleanup the pruning debris.
Natural preditors: ladybugs, lacewing, hoverflies, parasitic wasps and plant bugs.
Sprays: Horticultural oil based sprays, neem oil or insecticidal soap sprayed just as the new growth is beginning to form; around the time that magnolias are in bloom is the most effective time to spray. Heavily spray both sides of the leaves until the plant is dripping. This is a contact spray and the larvae must be covered in the spray. Once the leaves cup it is to late to spray as they are protected inside this shelter. Once the adults emerge you can begin spraying them until they lay their eggs.
Chemicals: There are several insecticides available for use against boxwood psyllid. Check what is legal to use in your region. The systemic insecticides acephate will control adults in June. Other systemic chemicals are applied either in the fall or a couple of weeks before nymphal feeding is expected in the spring.
There are other insect pests that are sometime confused with boxwood psyllid such as wooly aphids and boxwood leaf miners. However the cupping of boxwood leaves is unique to boxwood psyllids. Their damage is not as serious as leaf miners but due to the insect laying the eggs deep within bud scales and cupping the leaves over the nymphs, large populations can be difficult to control.
Photo Credits: all photos taken by the author.
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