Five Common Houseplant Pests

Take a good look at your houseplants this winter. Are they looking as healthy as you like? Chances are if they are looking a little peaked they may have one of the five most common houseplant pests. These chances increase if you had a tropical plant that was kept outdoors, and you decided to winter it (such as a hibiscus), or you set your other houseplants out for the summer.

Pest number one:

Mealybugs

Mealybugs are a common problem on houseplants. There are easily visible the naked eye. Mealybugs are leaf suckers that can cause new growth damage and introduce systemic damage to the plant. Bad infestations can cause leaf drop and distorted growth.

This hibiscus plant has been infected with mealybugs. Note the leaf distortion and curling.

Mealybugs have soft white bodies and are usually clustered at the base of leaves (axils) and on the underside of laves along the veins. Mealybugs eggs sacks often look like small tufts of cotton as they have been encased in a cottony wax.

From a distance mealybugs look like mold or white spots, further inspection shows individual insects with cottony wax around them.

Pest number 2:

Spider mites

Spider mites can be deadly to houseplants. Thy are very tricky because they are so hard to see. Colonies can seemingly appear over-night, but in fact they have been there for many weeks, even months.  This is another reason why its important to keep your houseplants clean; so you can see tiny indicators such as webbing given off by the spider mite.

Note the webbing on this plant caused by spider mites. turn leaves over and check for small insects and small brown spots on leaves. If you notice this treat immediately.

Spider mites can be hard to control simply because once they are spotted, they generally have taken over a plant. Spider mites are leaf suckers, that penetrate the outer cell layers on branch tips and leaf axils.

Spider mites are very common outdoors on Roses, Burning bushes, and Alberta spruce. They can be distinguished by leaf wilt, leaf loss, and browning and loss of needles.

Note the browing on this Alberta spruce. It has been caused by spider mites and needs immediate treatment.

Pest number 3:

Whitefly

Whiteflies in our northern area are restricted inside to houseplants, but can be introduced seasonally outside in warmer temps. Whiteflies have a six stage life cycle. The three stages that are most damaging are the instar phases when the insect is a leaf-sucker that rarely moves from its feeding position. It is hard to see the nymphs in this stage because they are almost transparent. Key indicators that you have whitefly are the adults. They can most commonly be seen when you move a plant, and when you water. Their bright white color is easy to spot.

Note the nymphs (clear bodied) and adult white fly. Nymphs cause the plant damage in the life cycle of the whitefly.

Heavy infestation can cause stunting, yellowing of foliage, and leaf drop.

Pest number 4:

Aphids

Aphids are an extremely common problem on Hibiscus, Bougainvillea and  Mandevilla vines. In an infested plant  you can commonly see aphids removing sap from new tender growth. This includes leaves and flower buds. If left untreated, aphids can causing leaf distortion and bud loss.

Aphid damage can range from leaf distortion to bud and leaf loss, and can eventually kill a plant if left untreated.

Outside, aphids are spending the winter on a mustard family plant (the only northern host plant for this cycle) as an egg. In the late spring they will move to their host plants and continue the cycle reproducing in September and October. There are over 47 spp of aphids that produce overwintering eggs in North America and 13 that produce eggs through the season.

Aphids can be identified by the two "prongs" on their abdomen. They tend to feed in large groups underneath leafs, on flowers and on tender stems.

Pest number 5:

Scale (soft and armored)

There are many types of scale that affects all forms of plants from pine trees to cactus. I am going to give some blanket information on two of those forms most likely found on houseplants.

Soft scale are the largest family of scale insects with around 1000 spp. Most are oval in form and have a raised, swollen center when housing eggs and crawlers. you can spot adults along leaves, leaf veins, and up and along stems where they feed on sap. They are mostly immobile in late adult stages, but young crawlers can move about easily. Adult scale can produce up to several hundred eggs. Common soft-scale on houseplants are the Hemispherical scale. Its host plants include ficus and schefflera plants.

The brown soft scale is a spp most commonly seen on houseplants.

Armored scales secrete a hard waxy cover. Most are oval, but in many spp that don’t feed on houseplants, they can be oyster and spiral shape. this covering is called a test which protects the abdomen of the insect and eggs. The actual insect is found under the test and is completely immobile after the first molt, with only its mouth-parts expanding through the cover. Common hard scale on houseplants includes the Boisduval scale, which feeds on a wide variety of tropicals but prefers orchids and palms.

This is an example of a European fruit scale that has been turned over to show its eggs.

A good indicator of scale on your houseplants is sooty mold. It is cause by the excess excretion of honeydew produced by the scale in which it feeds on. Sooty mold is not a pathogen to plants but should be cleaned with either soapy water or rubbing alcohol.

This is sooty mold on a Magnolia. Note the Magnoila scale above the leaves.

What to do when you have spotted these pests:

The first thing you should do is isolate your plants from other houseplants. Insects can move quickly from one plant to another-even if they are far away from each other. Inspect all plants for infestation, if you suspect a plant may be starting to have a problem you can treat it with systemic insecticide. Watch this plant carefully, as the problem may develop within the next few weeks.

The next step (esp with aphids and bad infestations of spider mites) is to remove the heaviest infected areas. Cut these small branches off and use Elmers glue to seal the wound. Remove parts immediately.If you can pick each insect of.  Use a kleenex to wipe and gather them, removing as many as possible.

Try knocking aphids onto a piece of tape when removing them. Don't stick tape to leaves or plant as it will surely damage it.

Clean! Clean leaves with rubbing alcohol to remove sticky residue, and any eggs. This will also further help remove any insects.

Treat! Now its time to treat your houseplants. You may want to try a few different methods. Never assume a chemical is safe for your variety of houseplants-some a very sensitive to chemicals so read labels, and ask questions.

Systemic chemicals are applied to the soil and taken into the plant though water. When an insect feeds on the plant, or lives in the soil it is exposed to the toxin.

bonide makes a systemic granule that can sucessfully treat most houseplants from common insect infestations.

Spray chemicals can be a direct and quick method and may in some cases be used in combination with a systemic granule.

Safer Houseplant insect spray is effective in treating aphids, spider mites, scale and whiteflies. Repeat treatment evry 7-10 days.

Natural alternatives include Neem oil mixed with water. Mist the plant one a week or as instructed. You may also try spraying a mild dish soap/water mixture.

Start over. If the plant is not special to you, you may just want to start over if the problem is bad. Don’t risk infecting all of your houseplants by keeping one infected plant around.

How to avoid infestation:

Do not dust your houseplants with a feather duster. This can transfer eggs and small insects from one plant to another.

Wash your houseplants. Wash leaves with luke-warm water to avoid the buildup of dust and grime. This will also help your plant achieve the highest rate of photosynthesis, keeping it strong and healthy.

Always use sterilized potting soil. That means no soil out of your garden! Do not use bags of soil that have been sitting open for long periods of time as they may have become infested.

Inspect your plants regularly. Look at both the tops and bottoms of leaves, and on the soil as you water. Early detection is key to stopping the problem.

When you bring a new plant home keep it isolated. There is nothing worse than knowing you have infected your great-grandmothers 75 year old Christmas Cactus (trust me I know). Wash the leaves with a warm-mild soapy water. After a few weeks, when you are sure there are no pests, than feel free to place it with your other plants.

Happy hunting!