Houseplants

Irene Shonle

02/22/2007 - Houseplants are a wonderful way to beat the winter blues up here.  They are green and growing when there are only bare branches and snow outside. Some give us color and fragrance, too!  My current cheap favorite is sweet peas from seed – if properly cared for they bloom for months and have a lovely sweet smell.

  Although they bring us joy, houseplants can also bring woe as they are uniquely susceptible to attack by many insects and mite pests because of the benign climate of indoors and the lack of any natural predators.  Sometimes we even unwittingly bring home an infested plant, and the bugs can jump from that plant to the other ones in your home.  Infestations of scale insects (mealybugs and whiteflies) are almost always established from infested plants recently purchased or received as gifts. As a precaution, do not place new plants with existing houseplants for at least three weeks. A careful inspection at the end of this quarantine time helps determine the presence or absence of pests.

  Here is some advice on dealing with common household insects from Whitney Cranshaw, Colorado State University Cooperative Extension entomologist and professor, Bioagricultural Sciences and Pest Management.

Spider mites and aphids:  washing the plant periodically with a vigorous jet of water can be particularly effective for spider mites and aphids, which are readily dislodged.  This will not get rid of all of them, but it will help knock the numbers down.  Insecticidal soaps (potassium salts of fatty acids) are one of the most commonly available houseplant insecticides. These are used as dilute sprays (one to three percent concentration) and can help control many houseplant insects and spider mites.   Horticultural oils, which are diluted sprays of oils (petroleum distillates, mineral oils) are another strategy, and these act to smother the insects.

Fungus gnats:  these are the little bugs that resemble fruit flies that are flying around your plants.  They usually appear in the winter, and are often a result of excessively moist soil which favors the development of fungus gnats.   To prevent this, only water when the soil is dry to a depth of at least one inch.  You can also try a drench of bt (Bacillus thuringensis) as an organic means of killing the gnats.

Whiteflies:  regularly vacuuming up whiteflies with a handheld vacuum can help in controlling them. Yellow sticky traps can also be useful in reducing the number of flying insects, including whiteflies, winged aphids and fungus gnats. These traps are sold commercially or you can easily make them by cutting bright yellow cardboard and covering it with petroleum jelly or some other sticky material. However, trapping alone will not entirely eliminate problems because much of the population, including the younger stages, remain on or about the plants.  Horticultural oils may help as well.

Mealybugs:  sprays of alcohol, or alcohol dabbed onto insects, are well known as a useful control of mealybugs. However, using alcohol on plants may cause injuries such as leaf burn. Carefully test a small part of the plant if you attempt to use this method.

Sanitation. Seriously infested plants are often best discarded because they usually require lengthy and extraordinary efforts to control the pests. They may also serve as a source for infesting other plants.

Irene Shonle is the director of Colorado State University Cooperative Extension in Gilpin County. If you would like more information, come by the Gilpin Extension office, visit our new website: www.coopext.colostate.edu/gilpin/, call 303-582-9106, or email: irene.shonle@colostate.edu.  The Gilpin County Cooperative Extension is located at the Exhibit Barn, 230 Norton Drive, Golden CO 80403 (right next to the Gilpin Community Center).

  Colorado State University Cooperative Extension provides unbiased, research-based information about, horticulture, natural resources, and 4-H youth development. As part of a nation-wide system, Cooperative Extension brings the research and resources of the University to the community. Colorado State University, U.S. Department of Agriculture, and Gilpin County, Cooperating. Colorado State University Cooperative Extension is dedicated to serving all people on an equal and nondiscriminatory basis. No endorsement of products named is intended nor is criticism implied of products not mentioned.