Dealing with Houseplant Pests, Part 2: The 7 Most Common Indoor Plant Bugs and How to Eradicate Them
When we bring a plant home, they become a part of the family. We take responsibility for their care. And just like children or pets, plants are dynamic living entities that sometimes get sick. Even if you’ve been very lucky so far, chances are that sooner or later, your luck will run out and you will find yourself face to face with indoor plant bugs. This may require us to step outside our comfort zone and spend a little more time and energy tending to our plants, but that is the (occasionally nerve-racking) nature of caring for a living thing.
In this second installation of our series, Dealing with Houseplant Pests, we dive into the nitty-gritty of indoor plant pest control. We’ll take you through the seven most common indoor plant bugs you’re likely to encounter in your home at some point, as well as how to deal with them. And the pests have never looked better, thanks to the gorgeous illustrations by our own Assistant Manager and in-house illustrator, Cate Andrews.
The 7 Most Common Indoor Plant Bugs and How to Eradicate Them
Aphid damage is often most visible on tender new leaf tips, where you might find dense congregations of small insects busily sucking plant juices. Aphids have soft, sometimes translucent oval-shaped bodies and range in color. Afflicted plants may wither, with curled or deformed new growth.
Aphids reproduce asexually and rapidly (females are born pregnant!), with many population explosions and generations per year. They leave behind tiny pearls of a sticky substance politely referred to as “honeydew”. This substance can often attract the aphid’s business partner, the sugar ant. Never welcome in the home, ants can also cause houseplant damage by occasionally building nests inside pots and damaging roots with their burrowing.
To get rid of aphids, pinch or prune off any badly infested stems. Use a hose or sink sprayer to knock as many aphids off as possible (not so strong, you damage your plant of course), taking care not to miss any leaf axils or undersides. Repeat every few days to keep populations down. Aphids can be controlled with insecticidal soap or neem oil, but a strong stream of water is the most immediate way to keep the problem from escalating.
Thrip damage is similar to that of spider mites, leaving plants wilted with spotted or streaked leaves. Insects are barely visible, resembling tiny shards or slivers ranging in color. Though thrips and their larvae can be extremely hard to see with the naked eye, you may actually have better luck detecting them by their droppings – little black dots that show up on and around your plant. It may also help to gently shake a branch of your plant over a white piece of paper — the indoor plant bugs and their droppings will fall onto the paper, making them easier to see.
Spray infested plants thoroughly with water, followed by insecticidal soap or neem oil. Repeat once per week for two to three weeks.
Whiteflies are exactly what they sound like: tiny gnat-like white flies that move in little swarms around your plants. Infested leaves are often pale and limp. Treat whiteflies the same as thrips, first spraying with water and then an insecticidal soap.
Mealybugs are good at hiding until it’s too late, so keep an eye out for small cottony spots at the intersections of leaves and stems and on leaf undersides. Parasitized plants may yellow and drop leaves. The fuzzy coating around mealybugs often protects them from water or pesticides, so the best way to remove “mealy” is by hand. Use an alcohol-dipped cotton swab or tweezers. Repeat weekly, spraying with insecticidal soap to catch any you may have missed. Heavy infestations can also be controlled by using a systemic insecticide.
- Spider Mites
Barely visible, tiny spider mites are a force to be reckoned with. Damaged plants may appear mysteriously pinpricked or speckled, sometimes drooping for no reason or turning a sickly bronze color. Spider mites are arachnids and, like their spider cousins, make webs. When an infestation becomes more serious, webbing can often be found on the undersides of leaves. Early detection of these indoor plant bugs is important, since spider mites can do a lot of damage and spread rapidly, with eggs hatching only days after being laid. As with thrips, you can tap or brush leaves over a piece of paper and to identify spider mites, which may be visible as very tiny slow-moving dots that will leave streaks if crushed.
Clip any heavily infested stems and dispose in a sealed plastic bag immediately. Treat your plant with insecticidal soap and/or horticultural oil like neem, and repeat once a week for two to three weeks to eliminate any new hatchlings. Don’t use systemics, as mites can develop resistances to them. If you have a large collection of plants and find yourself dealing with a serious spider mite outbreak, you might consider releasing beneficial mite predators. Spider mites are often a problem in the hot stretches of summer or the winter months when we keep our heaters going because they love warm, dry conditions. Keep air circulating, water consistently, and provide extra humidity during dry periods.
- Fungus Gnats
We get a lot of questions about fungus gnats, which thrive on high humidity and moist soil conditions. You may find them hanging out around ferns, Marantas, or other moisture-loving plants. Fungus gnats are an unsightly nuisance. Fruit fly-like, they hop or fly about your plants, especially when disturbed. However, it isn’t the gnats that do the real damage. It’s their larvae in the soil that eat rotting material but also tender new roots. A serious infestation can weaken a plant over time, leaving it pale and drooping. Populations can grow quickly, since fungus gnats lay somewhere around 300 eggs at a time. The first thing to do if you detect fungus gnats is to let the soil dry out as much as you can without causing your plant stress, since fungus gnats require constant moisture to survive.
A surprisingly easy, effective method for controlling fungus gnats is hydrogen peroxide! Simply mix one part 3% hydrogen peroxide with four parts water and water your plant with the solution. The peroxide will make quick work of any fungus gnat eggs or larvae. It also happens to oxygenate the soil and flush out compromising bacteria and fungal growth, making your plants extra happy and healthy. You may have to repeat the treatment a few times to catch any new eggs laid by adults.
If this still isn’t helping, consider releasing beneficial nematodes (microscopic predatory worms) into the soil which can make quick work of fungus gnats, or completely repot and replace with fresh soil.
When an experienced indoor gardener spots a symptom of a pest problem, their first thought may very well be, “please don’t be scale!” Visible as immobile shell-like bumps attached to leaves and stems, they call to mind evil space invaders in waxy little ufos. These curious coatings effectively protect the insects inside as they suck the juices out of the host plant’s vascular system, leaving them weak and often yellowed.
Scale spread quickly, bearing hundreds of young in their little bunkers. The first step with scale is to remove it by hand. This can be tedious and depending on how large the plant and how serious the infestation, next to impossible. Use a cotton swab dipped in rubbing alcohol, a toothpick, or your fingernail to gently pry off the discs. These can be difficult to remove, so take care not to damage your plant.
Finish with insecticidal soap to catch any young scale insects still in their more vulnerable “crawler” stage. Repeat weekly. This is tedious, but worth it if you treasure the plant. Even when compared to other indoor plant bugs, scale can be persistent. You can first try treating with insecticidal soaps or horticultural oils like neem, and use systemics as a last resort.
One last quick note – we try to avoid systemics when possible, always preferring natural solutions like insecticidal soap and neem oil. However, for most of these indoor plant bugs, systemic insecticides can be used as a “last resort” sort of treatment. For more on different treatment methods for indoor plant bugs, see the first installment in our Dealing with Houseplant Pests series, here.
Have more questions? In Part 3 of our series, we’ll share an Q/A with our resident houseplant pest specialist, Kristiana. She’ll share a few personal insights into dealing with indoor plant bugs that she’s learned from caring for her collection of over 500 houseplants!