Insects on Houseplants

During the winter months, it is important to keep ahead of insects on your indoor plants. Many insects live happily in the warm conditions of a living room or greenhouse. They may enter the house from plants either recently purchased or brought in after spending the summer outdoors. Some insects may enter through windows or screens, and many insects hitch a ride on our clothing. The other day I was watering my plants and noticed more leaves than normal had dropped off my Schefflera plant. When checking the leaves, I found they were sticky with insect honeydew. I have a massive scale infestation, and only noticed it just now. It is important to watch plants carefully for development of insect problems as they can be easily corrected if detected early. If ignored or unnoticed, insect problems can become quite difficult to control and can devastate indoor plants. Insect infestations can reach large populations in a short time indoors because there are no natural controls indoors such as weather or predatory insects.

Only a small group of insects harm indoor plants. The most common are mealy bugs, scales, whiteflies, and spider mites. Mealy bugs are soft-bodied insects and are usually covered with a white-powdery material. They feed on the plant with a piercing-sucking mouthpart that extracts plant juices. Mealy bugs are usually found clustered along leaf veins, on the underside of leaves and in hidden areas at leaf or stem joints. Their excess waste is excreted from the body in a form that is referred to as honeydew as it contains a high amount of sugar and is very sticky. Many times this sticky substance is discovered on the leaves before the insect has been detected. Some methods to control mealy bug include attempting to remove them using a cotton swab dipped in rubbing alcohol or by dislodging them with a strong stream of water.

Scales are also insects that excrete honeydew. Scales can be found on both sides of the leaves as well as on the twigs and branches. Scales are small, soft-bodied insects that are covered and protected by an outer waxy coating. Scales have piercing-sucking mouthparts and damage the plant by sucking plant juices. Scales are many times located along the veins of plants, or hidden in the crevices of stems or leaf axils. Many times you will discover a scale infestation by the sticky substance on the leaves of the plant, or you may notice yellowing or wilting leaves. Scales can many times be rubbed off the plant by hand or with a toothbrush or cotton swab soaked in alcohol. Heavily infested plant parts can be pruned out and disposed of.

Whitefly can be one of the most difficult indoor plant insect pests to control. They fly off the plant when disturbed, and the white appearance is very obvious. Whitefly have piercing-sucking mouthparts and are more closely related to scales and mealy bugs than flies. Their damage is similar as they remove plant juices and can cause the plant leaves to be mottled and yellow. If indoor plants are infested with whitefly, you might consider disposing of the plants. If outdoor temperatures allow, whitefly populations can be adversely affected by outdoor weather conditions and predatory insects that feed on the whitefly; thus, placing plants outdoors will be beneficial in controlling the insect. A vacuum cleaner can also be used to vacuum up the adults as they fly, but you need to continue this as more adults will emerge over time from eggs laid in the soil.

Spider mites are very common plant pests. They reduce plant vigor by sucking plant juices, and many times leaves turn yellow and drop. Spider mites are not insects, but rather belong to a class that contains ticks and spiders. They are very small and difficult to see with the naked eye. Spider mites have eight legs instead of six which insects have. Many times spider mites produce a fine webbing that may be spotted on the plant, and plants infested with spider mites generally look unhealthy. When a leaf or branch is tapped over white paper, small specks that appear as pepper or dust may be seen to move.

Information for this article was obtained from the Missouri Botanical Garden Hortline Guidesheet series.

Mary Kroening, Missouri Master Gardener Coordinator and UMC Horticulturalist, (573) 882-9633