Bonsai is the art of maintaining miniature plants through an exacting regimen of pruning and care. As with their standard-size counterparts, bonsai plants are subject to disease and insect pests, but because of their exacting growing conditions, they may suffer adverse effects more quickly. Promptly treat any signs of insects or disease, such as sticky dropping leaves.
Sticky falling leaves are almost always caused by aphids or scales. Aphids are small insects that live on the undersides of many ornamental plants, including bonsai. They may be brown, green, red or grey, and are usually wingless. Scales are very small, wingless insects that live in colonies on the twigs and stems of bonsai and other ornamental plants. They have an overlapping appearance that resembles scales. Both insect pests suck the sap from bonsai plants, causing the leaves to turn yellow, wilt and drop. They secrete a sticky substance known as honeydew.
Look under the bonsai plant's leaves for aphids. They may also hide inside curled leaves. Ants feed on honeydew and are often present during aphid infestations. Examine the twigs and branches of the bonsai for scalelike growths.
Take the bonsai outdoors if it is a houseplant. Wash it with a steady stream of water, covering the undersides of the leaves as well as the tops. Spray the plant with insecticidal soap, covering the plant completely. The soap coats the soft bodies of aphids and scales, drying them out and killing them. Rub the scales off with a soft cloth.
Some plants are more susceptible to aphid and scale infestations than others. When selecting a bonsai plant, choose one that is disease- and insect-resistant. Give it the proper amount of light, water and fertiliser required for that particular plant, and prune it regularly to maintain its health and shape. Healthy bonsai plants are better able to withstand disease and insect infestations.