Below is some basic information on the most commonly-encountered pests/insects on houseplants in the home. Bear in mind that soil-borne pests are no longer an issue in hydroculture and that even the leaf dwellers are minimized and easier to contend with. Even so, many visitors to this website have soil-grown plants and since a lot of areas of this website offer general information that applies to both conventionally and unconventionally grown houseplants, a similar page for pests is warranted.

I have also written further details about some of the pests listed below in Hydro Log articles, which I have linked to.

	Aphids		Fungus Gnats
	Mealybugs		Millipedes
	Spider Mites		Scale
	Whiteflies		Thrips

Aphids

        
Photographs by: Clemson University (USDA Cooperative Extension Slide Series)
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What are they?

Aphids are also called greenfly or plant lice. They are small, pear-shaped insects that can be winged or wingless. Most aphids are pale green although they can also be red, orange, yellow, black or brown. Aphids gather in colonies on the undersides of leaves, on succulent stems, and on flower buds

Damage

Aphids are tiny sucking insects that extract plant juices causing leaves to wilt and curl and eventually yellow and fall. Aphids puncture individual cells causing plants to lose their green color and appear sickly. These pests secrete honeydew, which can bring about the growth of black, sooty mold. Aphids are also carriers of viruses that they inject into the plant while feeding. If left unchecked, these insects have the potential to build up rapidly.

Control

A natural control is predator insects such as green lacewings and lady bugs. Lady bugs love snacking on aphids. Yum. Yum. Insecticidal soaps are also quite effective. Other natural alternatives are a hard spraying down in sink or shower as well as a thorough washing of the plant.

For more information: If You Grow Them, They Will Come

        
Photographs by: (1&2) Whitney Cranshaw (Colorado State University); (3&4) Gerald J. Lenhard
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I hate these things. They keep coming back again and again…until you switch to hydroculture. Then they’re gone forever. But for information’s sake…

What are they?

Fungus gnats are small, black, delicate flies that are often found hovering around plants with damp soil.

Damage

Fungus gnats - adults - don't do much harm besides being annoying and flying up your nose occasionally but their larvae can do considerable damage. Fungus gnats do not feed on or around your plants but simply lay eggs in the soil. These eggs hatch into white, black-headed, legless maggots (oh gross!) that mostly feed on fungi and decaying material but may attack plant roots and cuttings.

Control

Larvae thrive in wet soil but don’t do well at all in dry soil. To get rid of them, the larvae have to be dehydrated or they will continue to make more and more and more generations of gnats; and they do it very quickly. Let the soil dry out considerably – adults only lay their eggs on the top layer of soil and it has to be most; larvae also live on the top layer of soil - so they can dehydrate. Avoid soil that is too wet thereafter or the fungus gnats will return and the problem will start all over again. As for the adults, you can use sticky tapes, found at most greenhouse stores, to trap them. But with hydroculture, you’ll never see them again…adults or larvae…

For more information: Fungus Brats

        
Photographs by: (1&2) USDA ARS Photo Unit (USDA Agricultural Research Service);
(3) Alton N. Sparks, Jr. (The University of Georgia); (4) Anne W. Gideon
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What are they?

Mealybugs are small, pink insects that cover themselves with white, waxy material. They look like little tufts of cotton or small grubs that have been rolled in flour. Because of their ‘cottony’ appearance, they are often mistaken for a houseplant disease.

The eggs are also covered in this material, giving the appearance of bits of white fluff on leaves, stems and at nodes. Reproduction is rapid therefore steps to eradicate them should be taken swiftly.

Damage

Like aphids, these pests excrete honeydew which leaves sticky patches on the leaves, stems and axils of plants. They are sap-sucking insects that weaken plants by their feeding method causing stunted, hindered growth and eventual death of the plant.

Control

The white, waxy coating is there for a purpose – to protect the insect. This coating protects from sprays and makes it difficult to deal with this bug. Hand-picking and thoroughly washing provides the best type of control. Touching each insect with a Q-tip dipped in alcohol will also kill them. The babies are very small and sometimes overlooked, so be thorough or you will easily have a recurrence. Check daily until there are no further signs of them and you are confident that they have been eliminated.

For more information: The Root Of All Evil

        
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What Are They?

Millipedes are not really insects but are often found in houseplant pots and therefore considered as one of the pests you have to deal with. They are distant relatives of lobsters, crayfish and shrimp. Unlike their marine cousins, they are land dwellers that prefer moist habitats and areas of high humidity.

They have long, many-segmented, hard-shelled bodies with two pairs of legs on each segment. They are light brown, dark brown or gray in colour and can range in size from a fraction of an inch to about 9 inches (23 cm) long.

Damage

Millipedes are more annoying than destructive. They are scavengers and prefer to munch on decaying vegetation but they do occasionally damage seedlings by feeding on their stems or leaves. Sometimes they chomp on small roots and bulbs as well.

Control

Repot! Repot! And did I mention repot?

Repot your infested plant in fresh soil and a clean pot (or sterilize the pot your plant was originally in)

For more information: Close Encounters Of The Slimy Kind

        
Photographs by: Rayanne Lehman (Pennsylvania Department of Agriculture)
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What are they?

Spider mites are not insects – they are more closely related to spiders and ticks - but they are one of the most frequent pests of houseplants. They are oval shaped and yellow or green in colour. You fall into a rare (and blessed) minority if you’ve never had to deal with these pests because they always manage to move indoors at some point.

If left untreated, they multiply rapidly and travel from plant to plant if they can until you have a severe problem. They can be difficult to see with the naked eye as they measure about 1/50th of an inch. To verify whether you have mites or not, place a white piece of paper under your plant’s leaves, tap the leaves and then watch to see if there are tiny moving creatures on the paper. If there are, you have mites.

Damage

Spider mites begin by feeding on the underside of leaves and then boldly expand their territory as their population explodes. They chomp their way from stem to stem and plant to plant by building webs between hosts and walking to new destinations. They are also spread by you – on your hands, clothing, feather dusters, watering cans.

They usually attack new leaves and buds but don’t bet on them stopping there. They pierce leaf surfaces with needle-like mouthparts and feed on the sap. Plants that are infested with mites will lose their vibrant colour and appear bronzed or washed-out. At the same time, you will discover fine webbing around the leaves, on the stems and in the axils. The bad news is that once you notice webbing, it’s an indication that there is a severe infestation.

Control

Once a plant is infested with mites, isolate it immediately. Mites are extremely contagious. Dry, warm air encourages spider mites not only to move in but to breed like rabbits so increase humidity if you want to have an easier time battling them.

Wash the plant with soapy water and repeat every few days until there are no more signs of this pest. Insecticidal soaps are also available; make sure to read the label to ensure that the mites are listed on the product.

After you’ve won the battle, mist frequently, wash the plant now and then with soapy water, and keep humidity levels higher to discourage another mite infestation.

Amen :)

For more information: The Mite-y Battle

        
Photographs by: John A. Weidhass (Virginia Polytechnic Institute and State University)
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What are they?

Scale are round or oval insects related to aphids. They are protected by a hard waxy, shell-like covering when they are mature with colours ranging from tan to brown to black.

Scale live under their tough, armored shells and feed on the plant while laying eggs for the upcoming generations. Adults are stationary but juveniles (crawlers) have legs and are quite mobile. Not only can they crawl but they're also strong enough to drop off a plant and move to another. They not only drop and walk, they also jump from one plant to another where leaves touch, spread by traveling on hands and clothing, get tossed onto plants by strong currents and even get a taxi ride to new homes by feather dusters.

They’re not even in a hurry to get to their destination. They can survive several days without food while they travel from plant to plant searching for a place to call home. Once they find that perfect spot, they stick their mouth into a leaf or stem, tuck their legs under and start building a protective shell. Once they're settled and the shell is built, they spend the rest of their lives there.

Damage

Scale sucks plant juices, stunting growth. They secrete a sticky honeydew which attracts ants and other pests. If you see ants – that have a huge sweet tooth - hanging around your plants, you may have scale (or aphids). The honeydew also encourages black mold growth.

These insects are usually found on stems and the underside of leaves but they can also be found on leaf tops. Unfortunately they often go undetected for a long time and build up to large numbers by the time they’re discovered.

Death of infested plants is possible in severe cases.

Control

Scale are difficult to eradicate. They multiply so quickly that it feels as though you're battling for eternity - and you usually are. You CAN win the battle but you have to be persistent. Don't give them an inch...

Rubbing alcohol - always a good treatment choice - strips the wax from the shells and dehydrates the insects. Dip a cotton swab in alcohol and touch each insect with it. Mature scale are best removed manually. One method is to scrub off as many as possible with a soft toothbrush. Of course, there's also the 'brute-force-method' when you're really feeling frustrated after having won long battles only to see reinforcements appear from beneath leaves - crushing them with a fingernail.

Juveniles should be dealt with as quickly as possible, before they build shells. Without their shells, they are vulnerable to insecticidal treatments like any other soft-bodied pest.

For more information: The Thugs Of The Insect World

        
Photographs by: (1) Central Science Laboratory (Harpenden Archives, British Crown);
(2) Scott Bauer (USDA Agricultural Research Service);
(3) Clemson University (USDA Cooperative Extension Slide Series);
(4) Ronald Smith (Auburn University)
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What are they?

Adult whiteflies are tiny ‘white’ flies that look more like moths than flies. They are covered with a white waxy substance and when they fly they can resemble tiny snowflakes. Clusters of whiteflies can be found gathered on the back of leaves.

How do you determine easily if you have a whitefly infestation? Well, if you move or water your plant and you see tiny bugs flitting around – resembling a snowstorm or a white cloud hovering over the plant – oh no – you’ve got whiteflies!

Damage

Whiteflies suck the sap out of your houseplants causing leaves to turn yellow, wilt and eventually fall off. They are not true flies but rather relatives of mealybug, scale and aphids (what a terrible family). Whiteflies also excrete a sticky substance that can result in the growth of mold.

The immature flies are called nymphs and suck plant juices right along with the adults.

Control

Whiteflies can be a little difficult to control because they seem to instinctively know when you’re getting ready to hunt them down. They leave the plant as soon as you try to spray them!

All joking aside, spray plant with a strong steam of water, wash with soapy water or with an insecticidal soap. Repeat process until there’s no more sign of this pest.

Whiteflies multiply like crazy so get rid of them as soon as possible! The immature insects are scale-like and don’t move; this gives you an opportunity to work on eliminating them before they fly!

As an extra aid, you can also hang yellow sticky traps to attract adults.

        
Photographs by: (1&2) James P. Cuda (University of Florida); (3) Joseph Berger;
(4) E. Bradford Walker (Vermont Department of Forests, Parks and Recreation)
* click for a larger format *

What are they?

Thrips are light brown or black, slender insects that are very hard to see because they are so small. The immature insects are white, yellow or orange.

In the adult stage they will fly to other plants if they are disturbed, which makes it difficult to detect them. By tapping the plant’s leaves over a white piece of paper you may reveal their presence. Another significant sign is dots of black excrement on the leaves that some species of thrips leave behind.

Damage

Thrips feed on the foliage, buds and flowers. They puncture the plant tissue and suck on the sap. Leaves become distorted and have a silvery, stippled appearance. The plant is left with permanent noticeable scars. They can be a serious problem in the home and must be dealt with quickly.

Control

You can spray your plant with a strong jet of water or with an insecticidal soap. You can also wash your plant with soapy water. Yellow sticky tapes can also be used to help trap some of the adults.


* all photos above are courtesy of www.insectimages.org *

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