7 Houseplant Pests You Should Check For in December
Just because cold weather is here, it doesn’t mean all plant pests go into hiding! Join plant enthusiast Briana Yablonski to learn seven common houseplant pests to watch for this winter.
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When the dark, cold days of December arrive, I’m keen to spend my evenings in a cozy home. And it turns out I’m not the only one! While cold temperatures kill off many outdoor insects, common houseplant pests can thrive in your warm house or office.
If you’re not careful, aphids, spider mites, fungus gnats, and other small critters can overtake your pothos, philodendrons, and prayer plants. Fortunately, most of them are easy to treat, especially if you catch sight of them early.
I’ll introduce seven common houseplant pests to watch for in December, and ways you can both prevent and treat these unwelcome guests.
Spider Mites
Unlike many common bugs and diseases, spider mites like things dry and warm. That means they often show up in the winter when heaters and fireplaces create low indoor humidity levels.
Although there are hundreds of species of spider mites, the two-spotted spider mite (Tetranychus urticae) is the one most often found on houseplants. The adults resemble spiders more than insects, with eight legs and an oval body. However, since the mites are about 1/50 an inch long, spotting them with your naked eye is difficult.
Even if you don’t see the mites, you may spot another sign of their presence: a spider-like web. The mites create these fine-silk webs on leaves and stems, so if you spot a web, begin looking for mites.
You can also look for plant damage. Although a few spider mites aren’t concerning, large populations can lead to noticeable stippling on plant leaves. The mites use their sharp mouths to pierce leaves and drink plant sap. This feeding leads to small, yellow or white dots on the plant’s leaves. If you leave the mites untreated, this damage can lead to defoliation and even death.
Spider mite eggs hatch in a few days, and the nymphs mature into adults in one to three weeks. When you consider that each female can lay 100 eggs in her two to four-week lifespan, it’s easy to understand how a few spider mites can quickly turn into thousands. That’s why treating them as soon as you see them is important.
Prevention
Since spider mites often enter your house on infected plants, carefully inspect all new houseplants before you bring them inside. This monitoring also goes for outdoor plants you bring indoors for the winter. Make sure to check under the leaves, since this is where mites often hide. If you notice any of the pests, keep the plant in a separate part of your house and treat the mites.
Treatment
If you spot spider mites on one of your plants, start by moving it away from your other houseplants. A cool room is preferred to slow the mites’ reproductive cycle.
There are a few different ways you can treat spider mite infested houseplants. You can try to physically remove the mites with a forceful spray of water. Not only does this remove the mites, but it also increases the moisture and makes the environment unfavorable for the pests.
Another option is spraying the pest with insecticidal soap, horticultural oil, or pyrethrin. If you use any of these products, always follow the package instructions.
Aphids
Oh, aphids. They’re a bane of just about every type of gardener, so consider yourself lucky if you’re unfamiliar with them. With hundreds of species of aphids in the world, you can find one that attacks almost every type of plant, including houseplants.
Although there are a plethora of aphid species, they all share characteristics. They have soft bodies with eight legs and range from 1/16 to 1/8 of an inch long. Their pear-shaped bodies are green, black, gray, red, brown, or yellow, depending on the species.
All aphids have piercing/sucking mouthparts that they use to drink plant sap. When larger numbers of the insects are present, the leaves become discolored with a series of small dots. Infected plants may lose their leaves and become stunted. They may also become covered in honeydew, a sticky substance that the aphids secrete.
Prevention
I often recommend relying on natural predators like ladybugs and green lacewings for aphid control when dealing with aphids in an outdoor garden. However, you probably don’t want to release these good bugs in your house!
Therefore, the best way to prevent aphids is to avoid introducing them into your home. Carefully inspect any new plants you bring home, and consider quarantining them in a separate room for a week to ensure no aphids are present.
Keep your houseplants healthy overall by providing the proper soil, water, and light. Healthy plants are better able to fight off aphid attacks.
Treatment
The best treatment method depends on the number of aphids you’re dealing with. If you spot just a handful of the pest, you can wipe them off with a wet, soapy rag or spray them off with a steady stream of water. Make sure to look at the undersides of leaves since aphids often like to hide here.
If there are hundreds of aphids on one of your large philodendrons or palms, the options mentioned above may not be practical. Instead, you can spray the pests with neem oil or insecticidal soap. Coat both the tops and bottoms of leaves to contact all pests. If you still spot a few aphids a week later, wipe them off or spray again.
Thrips
A common pest of both indoor and outdoor plants, thrips are small insects that remain less than 1/5 of an inch long. There are numerous thrips species, but all of them cause similar damage. They pierce plant tissues and drink sap, leading to a silver or brown sheen on leaves.
Since thrips can be difficult to spot, you can use blue sticky cards to scout for them. The adults will fly to the blue color and become trapped on the cards. Note that if you do this outdoors, other insects that are attracted to blue will be harmed. If you spot more than a few thrips, you should treat your houseplant ASAP. Thrips reproduce quickly, so it’s best to tackle them before they have a chance to multiply.
Prevention
Since thrips are more likely to damage drought-stressed plants, make sure to keep your plants well-watered. You should still water less in the winter and let the soil dry out a bit between waterings. However, add water before all of the soil is dry.
Keeping your plants in moderate to high humidity will also lower the chance of thrips damage. Since heaters dry the air, you may need to utilize a humidifier in the winter to prevent the air from becoming too dry.
Another way to prevent thrips attack is to check for the pests before you bring new plants indoors. While you may not be able to see the pests themselves, you can look for the silvery sheen that indicates thrips are present.
Treatment
You can generally control thrips infestations with insecticidal soap or horticultural oils. These products coat the thrips’ tender bodies and suffocate them. Therefore, it’s essential to cover all of the plants’ surfaces to ensure you make contact with all of the thrips. You may need to make multiple applications over the span of a week or two.
If the previous sprays aren’t effective, you can spray insecticides that contain pyrethrin. Although this is an organic substance, it can still cause harm. Therefore, make sure to follow product directions when you apply it.
Whiteflies
These pests look exactly like what you’d think: tiny insects with white wings. Although they look like small, white moths, they are true bugs more closely related to aphids and mealybugs. The adults are around 1/10 of an inch long, and their wings are coated with a powdery, white wax.
The adults feed much like aphids; they pierce plant tissue and drink the sap. A few whiteflies won’t cause much damage to your houseplants, but large populations can lead to discoloration and defoliation. Over time, infected plants may exhibit stunted growth or an overall decline in health.
Whiteflies reproduce quickly and complete their life cycle in just a few weeks. The adults lay their circular or oblong eggs in clusters on the bottom of plant leaves. After the eggs hatch, the tiny nymphs move around the plant and feed on its sap. They eventually turn into moth-like adults that are capable of flight.
Prevention
Like most pests on this list, one of the best whitefly prevention strategies involves inspecting plants before bringing them inside. Even if you don’t see the adult whiteflies flying around the plant, there may be harder to detect eggs or nymphs present on the leaves. Therefore, keeping the new plant in a separate room for a few weeks is always a good idea to ensure it’s pest-free.
You can help prevent outbreaks by monitoring the pests with yellow sticky traps. The adults are attracted to the color and become trapped. While these traps aren’t effective control measures for large infestations, they can alert you to the presence of whiteflies.
Treatment
Yellow sticky traps can control the pests if you’re dealing with only a few whiteflies. However, they’re not a great option for larger outbreaks.
Spraying the pests with insecticidal soap, neem oil, or pyrethrins can provide adequate control. If the pests are still around after spraying, you may need to spray multiple times over two or three weeks. Disposal might be the best option if whiteflies are covering the plant.
Fungus Gnats
If you see tiny, dark fly pests hanging around your houseplants in moist December air, you’re likely dealing with fungus gnats. Although many people often mistake these slow-flying critters as fruit flies, they’re an entirely different species. Fungus gnats are less than a quarter of an inch long and look like flying dots. However, if you look closely, you’ll see they have long legs and antennae.
Although the adult fungus gnats are annoying, they aren’t harmful to plants. The larvae are what you have to worry about. The adults lay hundreds of eggs near the base of a plant, and the larvae emerge within a week. These larvae then feed on organic matter for the next two weeks.
They often consume peat moss and decaying plant matter but can also feed on plant roots. This feeding can weaken plants, especially when plants are small and/or there are lots of larvae in the soil. The larvae can also spread soil-borne diseases like pythium, fusarium wilt, and verticillium wilt.
Since fungus gnats can multiply so rapidly, they can quickly become out of control. Therefore, it’s best to start treating as soon as you spot them.
Prevention
Fungus gnats thrive in moist soil that’s high in organic matter. That’s why these pests often pop up in potting soil high in coco coir, peat moss, or compost. However, that doesn’t mean you must avoid soil that contains these materials!
Instead, monitoring and controlling the soil moisture is the best way to prevent these pests. Letting the soil dry out in between waterings will help prevent the pests from reproducing. Plus, most houseplants like it when their soil has a chance to dry out.
Treatment
If you spot fungus gnats, you can typically treat them by allowing the soil to dry out. The pests may still exist for a few weeks, but once they don’t have a suitable home to lay their eggs, they’ll diminish.
You can also take steps to kill the pests ASAP. Placing yellow sticky traps around the plants will attract and trap the adults. Applying Steinernema feltiae beneficial nematodes will help control the larvae since the nematodes feed on the pests.
Mealybugs
If you think you see moving dust or cotton on your houseplant, take a closer look. You may be dealing with mealybugs!
These tiny pests have soft bodies, but you would never know it thanks to their white coating that’s both waxy and fluffy. This coating helps protect the pests from moisture loss and heat, allowing them to survive in hot and dry environments.
There are numerous mealybug species, but they all have similar appearances and feeding habits. However, each species has preferred host plants. The citrus mealybug (Planococcus citri), one of the most common houseplant mealybugs, feeds on plants including coleus, croton, jade plant, and bird of paradise. While most mealybugs feed on above-ground portions of plants, some species feed on plant roots.
Mealybugs suck sap, leading to weak and stunted plants, defoliation, and general decline. The pests can feed on any part of the plant, but they often attack tender young foliage and stem tips. Citrus mealybugs also inject a toxin as they feed, leading to deformed tissue.
Some mealybugs lay eggs, and others give birth to live young. The citrus mealybug lays clusters of eggs covered by a white, cotton-like material. Some mealybug nymphs are mobile and slowly move around the plant, while others are immobile and quickly form a cocoon.
Prevention
I’ve said it before and I’ll say it again: check new plants for pests before you bring them indoors! Mealybugs can move from one plant to another, so bringing an infested plant into your home can cause your beloved plants to teem with these pests.
Treatment
Mealybugs can be harder to control than other houseplant pests. The nymphs often hide in crevices near newly emerging leaves and where branches meet the main stem, so it’s difficult for pesticides to reach them.
With that said, you can still effectively remove mealybugs from your plants. If there are only a few of the bugs present, thoroughly inspect your plant and spray them off with a stream of warm water. Alternatively, you can wipe them off the plant with a wet, soapy rag.
You can also try to get rid of the bugs by spraying them with insecticidal soap or neem oil. Although these products are effective, they must contact the pests. That means you’ll need to take extra care to ensure the pesticides reach bugs hiding in hard-to-reach areas.
If your plant is heavily infested, it’s often best to toss it and start over with a new plant. If you’re set on trying to save it, make sure to move it to an area that’s separated from your other houseplants.
Scale
Scale insects are an odd group consisting of around 8,000 species. The pests are very small, but the females protect themselves with a visible, protective shield. This scale-like coating ranges in size from 1/16 to 1/3 of an inch long and varies in color. It sits flush against leaves or stems and doesn’t move. That’s why some people mistake scale as a disease rather than a pest.
The female adults hiding under the coating are typically immobile. Most species lack legs when they become adults. The adults lay eggs or give birth to live young underneath the bodies.
These nymphs are mobile in their youngest stage, so they can venture away from their mother and find a suitable place to live. However, as they molt into the next stage, they become immobile and stay in the same location.
Both nymphs and adults pierce through plant tissue and suck the plant’s sap. Many of the pests also secrete a sticky honeydew substance that covers the plants. If enough of the pests are present, plants may experience yellow leaves and deformed parts.
Prevention
Always inspect new plants for scale before purchasing! Although scales are unlikely to travel from one plant to the next, it’s difficult to remove them once they’re present. Therefore, avoiding plants infected with scale is the best prevention strategy.
Treatment
The unique, protective coating makes scales difficult, but not impossible, to remove. If you notice the pests on your houseplants, you can gently scrub them with a soft-bristled toothbrush covered in soapy water. Make sure to check in crevices where the scales may be hiding.
Although spraying insecticidal soap or neem oil isn’t effective on adults, it can control the nymphs when they’re in their mobile stage. If you want to try spraying, make sure to pay close attention to the pests and spray at the right time.
