aphids, mealybugs, mites, scales, thrips, whiteflies
Growing Houseplants Without Using Pesticides
Houseplants bring nature, color, and beauty inside our homes. They're a popular way to make our indoor life more pleasant; about 75 percent of American families have plants in their homes.1 Occasionally these plants have problems with pests, but it's not necessary to use pesticides when this happens. This article is an invitation to try some pesticide-free techniques for keeping your houseplants healthy.
What Kinds of Pests are Common on Houseplants?
Houseplants can develop problems with a variety of insect and insect-like pests. Here are some common pests.2
- Mealybugs — These insects look like little bits of cotton that are greasy or waxy. They are oval in shape, have a segmented body, and are about 1/4 inch long. You'll usually find them hidden between leaves and stems or under leaves. They move slowly. They make a sticky liquid called honeydew and also cause leaves to become distorted and spotted.
- Thrips — These insects are also tiny, but shaped like a sliver. The adults have wings that fold up when they're not flying. You'll also see little black flecks (their excrement) scattered on the leaves. Thrips' damage to plants looks similar to the damage caused by mites but there won't be any webs.
- Aphids — Aphids are insects with winged and unwinged forms. They can be colored, powdery, or woolly. You'll find them on buds, the tips of stems, and under leaves. They're usu- ally less than 1/8 inch long and often make honeydew. They can cause plants to develop curled leaves.
- Whiteflies -- These insects look like tiny moths. They're only about 1/12 of an inch long. They can make honeydew and often cause the plant to look wilted and faded. The immature whitefly is flat, oval, and legless. Most often you'll find them under leaves.
- Mites — These tiny animals are related to spiders. They're so small that they look like little dots, often red, yellow, or green, moving on the plant. Mites typically make webs and some cause bronzing, yellowing, or browning of leaves.
- Scales — These are insects, but they don't really look like insects. They are usually less than 1/8 of an inch long and look like scabs or bumps. They can be a variety of colors: white, black, brown, gray, and tan. Like mealybugs, some scales make honeydew.
An Ounce of Prevention...
One of the most important steps you can take to prevent houseplant problems is to provide them with good growing conditions. Amy Dreves, with Oregon State University's master gardener program has these recommendations:
"Know your plants' needs and keep them healthy with adequate light, water and fertilizer. Stressed plants encourage pest problems. For example, high nitrogen favors aphids, while dry and dusty condi tions promote mite outbreaks."3
Houseplant experts believe that "watering is the most important (and most often abused) cultural practice."1 Tips for watering houseplants include using enough water to run out the drainage hole in your pot, only watering when the surface of the soil has become dry, and not allowing the pot to sit in excess water.1
Aphids thrive on plants that contain high levels of nitrogen. Adequate, but not excessive, fertilization will make your plants less attractive to aphids.4
You can also prevent houseplant pest problems by being careful not to allow them in your home. When you buy a new plant, inspect it to make sure that there are no pests on it. Sometimes they are hard to spot, so search carefully. Put new plants in a separate room for a few weeks and inspect again. If you put houseplants outside, inspect them when you bring them inside. When you repot your plants, commercial sterilized potting soil can be a better option than soil from your garden. If you pick up plants at stores or friends' homes, inspect first to make sure you're not picking up pests that you can then bring home.5
Many pest insects need places to hide in order to thrive. You can minimize pest shelters by removing fallen leaves from your pots.5Finally, reflections from aluminum foil disorient flying thrips and aphids. If you regularly have trouble with these insects, try placing a piece of foil around the base of your plant. It will make it more difficult for these pests to land.3
A Stitch in Time...
Nearly all pest problems are easier to deal with when there are only a few pests. Here are some tips to make finding pests easier:
- Look for pests regularly, every time you feed or water the plants.2
- Breathe on the plant and look for pests that react to your breath by moving.2
- Put a piece of paper under the branches or leaves of your plant. Then tap or brush lightly. Pests will drop on the paper. Use a magnifying glass to help identify them.2
- If you're looking for mealybugs, check for egg sacs on all parts of the plant, as well as the rim and the bottom of the pot.6
Trapping Flying Pests
Sticky traps for aphids and thrips are commercially available.7 Color is used to attract the insects to the trap; yellow attracts aphids, and blue attracts thrips.3 You can stake the traps into your plants' soil or hang them from larger plants.7 If you want to make your own traps, a simple technique is to fill a small colored dish with water and let the insects drown when they are attracted to the color.3
Hand Removal of Pests
Probably the most straightforward way to get rid of pests is just to pick them off the plant.5 If you don't want to touch them you can use a toothpick5 or a damp cloth.6 Washington State University extension agents Art Antonelli and Sharon Collman also recommend a cotton swab dipped in rubbing alcohol for aphids or mealybugs.5
A vacuum cleaner can be a useful tool for removing insects from houseplants, according to Oregon State University's master gardener program.3
A forceful stream of water is an effective way to remove some pests. Try this technique with aphids, whiteflies, mealybugs, thrips, and spider mites.8
Extension agents in Washington and Idaho recommend using sprays of soapy water to control houseplant pests.5,9 Some plants are damaged by certain soaps and "there is no complete list of plants which might be harmed by this technique."5 NCAP recommends that you start by testing your soap on small parts of the plant.
If only a few leaves of your houseplant are infested you can remove that part of the plant. Then dispose of the infested parts to keep pests from spreading.5
Disposing of Plants
If your plant is badly infested, it may be time to get rid of the plant. Cuttings of many houseplants will produce roots so you can actually keep growing favorite plants that have to be discarded. Be sure to discard the potting soil and wash the pot thoroughly.5
It's not complicated to have healthy, pesticide-free houseplants. Try the techniques summarized in this article when you need to deal with mites or insects on your houseplants.
- Washington State Univ. College of Agriculture and Home Economics. Cooperative Extension. 1996. Basic houseplant culture. EB1354. http://cru.cahe.wsu.edu/CEPublications/eb1354/eb1354.html.
- Oregon State Univ. Extension Service. 1995-2006. Garden hints: How to detect houseplant and greenhouse pests. http://extension.oregonstate.edu/news/story.php?S_No=186&storyType=garden.
State Univ. Extension Service. 1995-2006. Garden hints: How to
discourage and prevent houseplant pests.
[accessed Feb 14, 2006]
Similar text available at: How to control indoor plant pests without toxic chemicals. http://extension.oregonstate.edu/news/story.php?S_No=762&storyType=garden
- Univ. of California. Div. of Agriculture and Natural Resources. Statewide Integrated Pest Management Program. 2004. Pests of landscape trees and shrubs: An integrated pest management guide. Second edition. Publ. 3359. p. 109.
- Washington State Univ. College of Agriculture and Home Economics. Cooperative Extension. 1995. Houseplant pests. EB0695. http://janbowers.com/resources/gardening/houseplantspestid.pdf.
- Montana State Univ. Extension. 2001. How can I get rid of those little sticky white puffs on the leaves of my houseplants? Garden Guide 12(1). (January 2001). Text available at: http://gardenguide.montana.edu/article.asp?id=8
- Woodstream Corp. 2005. Instructions for house-plant sticky stakes. http://www.saferbrand.com/test/instructions/sticky.htm.
- Ref. #4, pp.109, 125, 129, 158, and 201.
- Univ. of Idaho Cooperative Extension. 2001. HomeWise. (July 15.) http://info.ag.uidaho.edu/homewise/homewise_071501.htm. (link no longer active)
This article was originally published as:Cox, Caroline. 2006. Growing houseplants without using pesticides. Journal of Pesticide Reform
Links updated October 2010