by Amy L. Stripe, Master Gardener Volunteer 2008
Types and Identification
Most common pests that prey on houseplants are fairly easily detected. Mealybugs are small (1/5-1/4 in. long), soft-bodied insects with a cottony appearance that cause leaf yellowing and hinder growth. Aphids are pear shaped, measure 1/25-1/8 in. long, and line up in groups on new growth, curling and distorting leaves. Scale insects vary from 1/8-1/3 in. long, can be almost any color and are surrounded by a circular or oblong waxy covering when mature. Scale insects can be found on both sides of leaves, twigs and branches, will reduce growth, cause leaf drop and yellow spots on tops of leaves. At 1/16 in. long, whitefly resembles a minute moth and inhabits the undersides of leaves which makes it difficult to detect – unless you disturb the plant, causing a swarm. This pest saps plant vigor. All of the above insects secrete a sticky substance called “honeydew” upon which sooty mold (a velvety black fungus) thrives. This is a sure-fire sign that you’ve got an infestation.
The most difficult of the common pests to detect may be the spider mite, a sometimes colorless, virtually microscopic bug that infests the undersides of leaves, giving the upper side a mottled look. Apart from these symptoms, the presence of fine webbing on the leaves is another sign.
Aphids and mealybugs can be removed with a cotton swab dipped in alcohol; don’t overdo it, though, as alcohol can burn foliage. Washing foliage in soapy water* will remove aphids, mealybugs and scale insects. If bigger guns are called for, use a commercial horticultural oil**, which will be effective on all five of these pests, or insecticidal soap. Be sure the product is specifically labeled for houseplants. Don’t use general household insecticides (for cockroaches or flies) since they can damage foliage. Follow instructions carefully and take plants outside to apply.
Prevention is easier than the cure. Before bringing any plant into your home, inspect it carefully. Keep it isolated from your other houseplants for several weeks. A good cultural practice is to spray tops and bottoms of foliage with a strong stream of water (in the shower, laundry sink, or outside with a hose) every two weeks to remove dust and many insects before they get a toehold.
*2 tsp of non-degreasing dishwashing detergent per gallon of water
**Neem or similar
Remember that many of the most popular houseplants are natives of the humid, shady understories of hot tropical forests. Replicating the humidity that many of these plants require can be difficult. Try periodic misting or placing pots on wet gravel beds.
For more on houseplant pest control visit: https://gardeningsolutions.ifas.ufl.edu/care/pests-and-diseases/pests/ https://ufdcimages.uflib.ufl.edu/IR/00/00/28/82/00001/MG00400.pdf
For more on caring for houseplants go to: https://gardeningsolutions.ifas.ufl.edu/plants/houseplants/