Unidentified Indoor pests- Check the Houseplants
Winter brings an increase in infested potted plants
Houseplants are often one of the last places that the customer (and the technician) look for pests. When a customer complains of almost invisible mites crawling over a tabletop, you may be looking for brown dog ticks or a source for bird mites, when in fact, the source is the Scheffler plant sitting in the corner. Sometimes situations with invisible pests that are dubbed “ delusoryparasitosis” can actually be traced to very real pests from infected houseplants.
Houseplant pest infestations can increase in the winter for three reasons: (1) Houseplants that spent the summer outside on the deck have been brought back inside, along with unseen hitchhiking pests. (2) People purchase houseplants in winter months to bring a bit of green inside. Plants can be already infested when purchased from growers. (3) Drier indoor air is actually a plus for some of these pests, particularly spider mites, and previously low-level populations can explode quickly in winter.
How to tell if Houseplants are infested
With the exception of the winged forms of fungus gnats and whiteflies, most plant infesting pests don’t usually leave their plants unless the plant is dead, infestations are heavy, or they are knocked off. Houseplant pests are most often found on the underside of the leaves (the top of the leaves may look fine), requiring a close-up inspection. It will help if you use a magnifying hand lens and a flashlight.
1. Insects or mites moving about or clumped together, or tiny white eggs, pupal cocoons, or black fecal specks on the bottom of the leaves. Hold a piece of stiff, white paper under the leaves, then tap several leaves over the paper to dislodge insects.
2. Sticky droplets of “honeydew” sap exuded by the pests on the leaves, or a gummy feel on the table or other surface beneath the plant. Ants may be attracted to the honeydew.
3. Whiteflies or fungus gnats flying off of the plant momentarily, and then settling back onto the soil or leaves.
4. Thin webbing spun between the stems by spider mites, shine a flashlight to see the webbing and look closely for tiny mites moving along the webbing.
5. Stippled leaves covered with tiny yellow or white feeding punctures. Eventually, the leaves will turn pale, coppery, or silvery, and may drop prematurely.
What are the pests you’re looking for?
With the exception of the fungus gnat, houseplant pests suck juices from the leaves and stems. They include whiteflies, scale insects, mealybugs, and aphids. Probably the two most common houseplant pests are fungus gnats and spider mites.
Fungus gnats- This is the houseplant pest that most technicians are already familiar with since the tiny,black adult flies leave the plant and fly about indoors. The fly larvae live in the upper layers of the soil where they feed on decaying organic material and sometimes damage roots. The resulting adult flies run on surfaces in a jerky manner or fly to lights or windows. Fungus gnat larvae in potted plants are always associated with overwatered, too wet potting soil and are easy to eliminate just by letting the soil dry out between waterings.
Spider mites- Spider mites vary in colour and are about the size of period at the end of this sentence. You will find them on the under surface of leaves, along with eggs and shed mite skins. In heavy infestations, you can see loose silken webbing connecting stems with mites moving along the webbing. Infested plants may be stunted in growth and drop leaves prematurely. Spider mites thrive in hot, dry conditions while cool, humid, or rainy weather keeps mite populations down. Drought-stressed plants are especially susceptible.
What can be done about Infested Houseplants?
There is always the very real risk that one infested houseplant will infest others, particularly when plants are touching allowing pests to crawl onto a new plant. Fungus gnats and whiteflies can fly to infest a nearby plant. Mites or other houseplant pests that are found off the plant usually die soon and don’t require any special control.
Most houseplant pests, and particularly spider mites, can be very difficult to get rid of completely, requiring repeated applications of insecticidal soap or oil, or soil insecticides. Depending on their value, it is often best just to discard infested houseplants.