New Utah Pests Fact Sheets:

UTAH PESTS Staff 

Houseplant Pest Blues

Have you ever purchased a beautiful poinsettia for the holidays, only to find out (two weeks later) it was completely infested with whiteflies?  How do you try and manage a pest that has spread to all of your favorite houseplants?  Unfortunately, indoor pests are a common problem that can become a chronic issue if not controlled properly.  Most houseplant pests are transported indoors on plant material, either by purchasing new plants or relocating summer potted plants.  Common offenders include fungus gnats, mealybugs, scales, thrips, spider mites, whiteflies, and aphids. 

Adults are easily disturbed from the plant and are an obvious nuisance.  Fungus gnat larvae are the damaging life stage, feeding on roots and organic matter in the soil.  Repotting with new, sterile soil and reducing moisture will discourage egg-laying adults.  For widespread infestations, consider using a soil drench of Bti (Bacillus thuringiensis israelensis) to kill larvae, and sticky cards to trap adults.

Spider Mites

	Top:  Fungus gnat adults and larvae thrive in moist soil conditions. Bottom:  Spider mites often go unnoticed until leaves are heavily infested and webbing covers plants.

Mealybugs / Scales / Aphids

These fluid-feeding insects can feed on any part of the plant and often go unnoticed  until the leaves turn yellow or drop off.  Mealybugs and scales are cryptic insects that cover themselves in a protective, waxy or cottony covering.  Honeydew will be sticky and obvious on the plant, and can promote a black sooty mold if not washed off.  Diluted alcohol (25% concentration), insecticidal soaps and horticultural oils are the most effective management tools.  Armored scales are particularly difficult to manage, and insecticidal soil drenches (imidacloprid) may be necessary for large infestations.  

House Plant Pest Control

			Green peach aphids are common greenhouse pests that are accidentally introduced into homes.

New houseplants or existing outdoor plants should be isolated from healthy indoor plants for at least 2 to 3 weeks to confirm they are pest-free.  Regularly and thoroughly examine household plants to detect early infestations.  Sometimes the insects are cryptic or live in the soil, and assessing current activity can be difficult.  So look for cast molting skins, feeding injury, or honeydew.  To confirm an infestation of mites, thrips or springtails, gently shake the plant in a bucket or over a piece of paper and look for moving “dust.”

If a houseplant infestation does develop, there are several techniques that may help eliminate or suppress pest activity.  Periodic washings of some plant types may help dislodge small insects and mites.  Yellow sticky cards are attractive to most flying adult insects and can be used near infested plants.  Sometimes, severely infested plants should be discarded because nursing sick plants can be a time-consuming and futile effort.

Although many synthetic insecticides are available for houseplant pest control, it is important to recognize many persistent pests are genetically resistant.  As a result of overuse in greenhouses and nurseries, many species of whiteflies, aphids, and fungus gnats are no longer susceptible to conventional insecticides.  Microbial products made from bacteria, nematodes, or fungi are selective; these products are most effective in humid conditions and multiple applications are often necessary.  Horticultural oils and soaps are generally effective against most houseplant pests.  Botanical products, like neem and pyrethrins, are relatively fast-acting insecticides with a short residual.  Systemic soil drenches target fluid feeding insects, but take time to circulate throughout the plant.  Occasionally, a “host-free” period of houseplants may be a more effective (and cheaper!) treatment for a serious indoor plant pest outbreak.

For more information, go to the UTAH PESTS Web site and search for the fungus gnats and soft scale fact sheets at www.utahpests.usu.edu/insects/htm/factsheets.

-Erin Hodgson, Extension Entomologist (No longer at USU) 

Picture of the Quarter 

The tiny ant-like flower beetle (Ischyropalpus sp.) is an omnivorous feeder, and some species are considered to be important biological control agents.  It feeds on eggs, larvae, and nymphs of small prey, as well as sap, pollen, nectar, fungi, and detritus.  Males collect droplets of the chemical cantharidin from dead blister beetles and pass it on to females for protection from predators.   -Photo by Marion Murray