Utah Pests News Winter 2008-09

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New Utah Pests Fact Sheets:

Carpenter Ants
Carpenter Bees

Clothes Moths

Fungus Gnats
Human Parasites
Squash Bug 
Yellow Sac Spider


Diane Alston 
Entomology Specialist  

Ryan Davis
Insect Diagnostician 

Kent Evans (No longer at USU)
Plant Pathology Specialist 

Erin Frank (No longer at USU)
Plant Disease Diagnostician 

Erin Hodgson (No longer at USU)
Entomology Specialist 

Marion Murray
IPM Project Leader 
Editor, Utah Pests News

Utah Plant Pest Diagnostic Lab
BNR Room 203
Utah State University
5305 Old Main Hill
Logan, UT 84322

Utah Pests News is published quarterly by the UTAH PESTS staff. 





Additional articles in this issue:

A New Virus Possible on Tomatoes

Abiotic Diseases of Spruce and Other Conifers

Tree Fruit Monitoring Summary for 2008

Biocontrol Agents are Working Hard in Utah

Common Spruce Insect Problems

Spotlight: Salt Lake County Jail Horticulture Program

IPM National News and Useful Publications

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.

Although not an insect, spider mites are common houseplant pests.  Small infestations start out on the undersides of leaves and can spread throughout the entire plant. Initially, leaves look speckled or yellow, but eventually heavily infested plants will be grey, dusty, and covered with webbing.  Increasing the humidity around houseplants can be helpful; also, vigorously washing the leaves can remove all life stages.  Horticultural oils provide more effective control than insecticidal soaps or sprays.  

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.
Indoor infestations can be minimized with a few simple strategies.  The most important cultural control tactic is to keep plants healthy with proper watering and fertilization.  Optimal vigor will depend on the type of plant – some like their roots to dry down between waterings while others thrive on having “wet feet.”  Excessive soil moisture favors soil-dwelling insects like fungus gnat larvae; however, drought-stressed plants can flare spider mites and aphids. 

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