Laburnum, or the golden-chain tree, is a small deciduous tree or tall shrub enjoyed primarily for its stunning clusters of yellow flowers that hang on the tree for about two weeks in late spring or early summer. Laburnum species are often considered difficult to grow because of their environmental and site requirements. A pest problem -- although these trees are fairly resistant to pests -- can make members of the Laburnum genus even more difficult to cultivate.
Leafminers are insect larvae that feed between leaf surfaces creating a winding mine or blotch that appears on the leaf surface. The most prevalent leafminer on laburnums is probably of the genus Leucoptera. Several natural parasites may keep this leafminer under control. Deal with a leafminer infestation by pruning off and destroying infested branches. If necessary, apply a foliar spray of imadacloprid as soon as leafminers appear.
Spider mites are tiny relatives of spiders and ticks that feed on laburnum leaves and give leaves a yellow, stippled appearance. Severely affected leaves may turn brown and drop and the tree will suffer from a loss of vigour. The mites also leave a silken webbing where they persist. Predatory mites are effective at controlling spider mites. Other control options include removing heavily infested leaves on branches and ensuring that the tree has adequate water, spraying the tree with a strong blast of water and, if necessary, applying a miticide.
Several species of aphids, tiny, wingless insects, may feed on laburnum. Aphids generally feed first on shoot tips. On young trees, this feeding may cause malformation and stunting of branch tips. Encourage populations of natural aphid predators like lady beetles, lace wings and syrphid fly larvae. A strong spray of water can knock aphids off plants. Avoid excessive watering or nitrogen applications. Aphids can also be chemically treated with thorough foliar sprays of acephate, horticultural oil, azadirachtin, imadacloprid or insecticidal soap.
Adult female mealybugs are soft, oval and wingless insects that may be covered with a fluffy wax. Male adults are gnatlike with long tales. Eggs are minute but covered with an apparent white, fluffy wax, and older nymphs may also be covered with a white wax. These pests feed on any plant part and excrete sticky, sweet honeydew that hosts unsightly sooty mould. Provide plants with good cultural care to ensure plant vigour and control ant populations, as these pests protect mealybugs. If necessary, apply insecticidal soap, narrow range oil or a systemic insecticide.
Foliage-feeding caterpillars like the genista caterpillar may be a pest of laburnum in certain regions. Caterpillars may roll leaves together and feed on the inside, create silken "nests" or devour leaves and stems more openly. A heavy infestation may cause defoliation and branch dieback. Address problematic caterpillars by pruning and destroying infested foliage, scrape any apparent egg masses off the bark, use proper cultural practices to maintain tree health and, if the caterpillars feed openly, a spray of Bacillus thuringiensis controls caterpillars if it is applied shortly after these pests hatch.