The most common causes of pests on indoor plants are poor care or an unfavorable location. If the growth conditions do not match the needs of the plants, they are weakened and can no longer defend themselves against attackers.
8 common houseplant pests
If the leaves suddenly turn yellow and fall off, or if the plant no longer wants to grow properly or is covered in sticky drops, then insect pests are probably behind it. In our article you can find out which pests are particularly common on houseplants, how to recognize them and how to combat them in a targeted manner.
Tip: If your indoor plants are infested with pests, do not immediately resort to poison. In particular, pesticides marked with “T” or “T+” are highly toxic and have no place in a home. Instead, many proven and non-toxic home remedies help very well against common pests.
leaflets (nematodes)
Source: Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org, Aphelenchoides sp. Heuchera sanguinea (02), Edited from Plantopedia, CC BY 3.0
Aphids are tiny roundworms, only about one millimeter long, that live in water and spread via irrigation water. The little animals - also known as nematodes - get inside the leaves through the stomata and suck out the plant cells.
symptoms
Typical signs of an infestation with aphids are:
- first appearance of glassy spots on the leaves
- then brown coloring of the same
- Formation of distinct leaf spots
- Leaf veins not affected cannot be overcome by aphids
- leaf fall
If you suspect an infestation with eellets, cut up a leaf with scissors and put the pieces in a glass filled with water. After a while, if you look closely, you can see the tiny threadworms swimming on the surface of the water.
Causes and Prevention
The cause of an aphid infestation is always infected irrigation water. Therefore, never water your indoor plants over the leaves or ensure that they can dry off quickly after spraying or showering (which is often necessary with many tropical green plants). If you spend the summer outdoors, you should always place the plants in a place that is protected from rain and wind.
Source: Jody Fetzer, Maryland National Capital Park and Planning Commission, Bugwood.org, Aphelenchoides sp. on Buddleja spp. (03), Edited by Plantopedia, CC BY 3.0
Commonly infested plants
In principle, aphids can appear on almost all indoor plants, provided their leaves are not too firm or leathery. However, the pests prefer to attack these plant species:
- begonias
- ferns
- gloxinia
- hydrangeas
- hyacinths
- primroses
- African violets
In any case, avoid watering or wetting the leaves of the species mentioned.
combat
To get rid of the leaflets, you have to keep the leaves dry. Therefore, do not spray the infested plants with water, and the damaged parts of the plant must be removed to protect them from further spread. In the case of a severe infestation, however, the only thing that often helps is to dispose of the plant.
aphids
Various plant sap-sucking lice, such as aphids, are very common on houseplants. There are numerous different species, some of which are specialized on certain host plants. Typical of indoor plant infestations is the green peach aphid, which - like all lice - can multiply very quickly and occur in large numbers. Swift action is therefore immensely important.
symptoms
Aphids suck off the nutritious plant sap, thereby depriving the infested plant of important nutrients and at the same time damaging it by injecting salivary toxins. If you look closely, the pests can be seen on the undersides of the leaves in particular, but also on other soft parts of the plant. The following symptoms also indicate an infestation:
- Curling and curling of the leaves
- yellow leaf spots
- Atrophy of the shoot tips
- leaf deformations
- stunted flowers/buds will not open
- sticky coating on the leaves
The sticky coating is honeydew, the sweet excretions of the aphids. Not only do these often attract ants (who keep veritable aphid farms in the wild), they are also colonized by black sooty mold fungi. The leaves turn black, and the dark coating can be wiped off with a little rubbing.
causes
Aphid infestation on a rose
Aphids usually appear on plants weakened by improper care. They often get into the apartment through open windows and like to settle on plants that are exposed to drafts. Dry room air also promotes infestation.
combat
A lot of patience helps against these pests, which are as annoying as they are stubborn, as they cannot be driven away by one-off measures. Shower off the infested plants with a strong jet of water, and a large part of the tiny insects will already be eliminated. Wipe off sticky and blackened leaves and spray the houseplants several times a few days apart. A soap solution or a nettle extract is suitable for this.
Produce it as follows: Soak 500 grams of fresh, finely chopped nettle leaves (cut before flowering!) in five liters of water for 24 hours. Immediately spray the affected plants with the undiluted brew. Always use fresh stock! The soap solution is also very effective, but not all plants tolerate it. Therefore, test compatibility on just one or two leaves first before spraying the entire crop.
Tip: There are numerous very effective beneficial insects against aphids. Lacewings, gall midges, parasitic wasps and ladybirds can be bought in specialist shops and applied directly to the spot. As soon as there are no more aphids, these insects disappear and look for new hunting grounds.
scale insects
Scale insects are also plant sap-sucking lice that act in a similar way to the aphids described and also cause comparable damage. There are several species, which, as a rule - unlike other plant lice - from adult animals are immobile and hide under a brownish, solid shield. The wingless females and their clutches and, in some species, also the larvae sit under this shield.
symptoms
A scale insect infestation leaves damage to the infested plants, similar to that described for aphids. If you look closely, you can also see small, brownish elevations, especially on the undersides of the leaves and on soft spots (e.g. shoot tips, leaf axils).
causes and treatment
Lice such as scale insects, but also mealybugs and mealybugs (which are basically just subspecies of scale insects) are difficult to combat because of their protective shields. They mainly appear after the winter has been too warm and when the room air is dry, which is why you should pursue the following strategies to combat them:
- Isolate affected plants, avoid contamination
- put in a cooler and brighter place
- Treat plants several times at intervals of a few days with a spirit and soap solution
Scale insects (Coccoidea). Source: Amada44, Coccoidea - 8670, crop from Plantopedia, CC BY-SA 3.0
You make this spray solution by mixing a good splash of washing-up liquid (alternatively a tablespoon of liquid soft soap) with a tablespoon of denatured alcohol in a liter of water. You can drip the solution directly onto the pests or spray the whole plant. Rinse tender-leaved species with clear water about 15 minutes after treatment to avoid leaf damage. Incidentally, leaf shine spray also helps with stubborn houseplants.
Tip: Never scratch the scale insects off the leaves, as there may be tiny larvae hidden under the scales that are invisible to the naked eye - scraping them off will only spread them further.
Black flies / fungus gnats
If you suddenly have a lot of blackflies in your home - maybe after you've recently bought a new plant or repotted your houseplants in fresh substrate - it's probably fungus gnats. The pests, which are up to seven millimeters long, look like fruit flies.
Fungus Gnat, Sciaridae
symptoms
It is not the adult flies that are among the pests on your indoor plants, but their larvae are dangerous. Fungus gnats lay their eggs in moist, loose soil, the larvae that hatch from them remain underground and feed on plant parts, especially roots. No damage can be seen above ground at first, but an infested plant soon looks unhealthy. Their water and nutrient absorption is disturbed, so that they can appear stunted and dried up.
Causes and Prevention
Blackflies usually get into the house through substrate contaminated with eggs and/or larvae. Therefore, it makes sense to sterilize plant substrate before repotting, for example by heating it in the microwave or in the oven. The potting soil should remain in the oven for at least half an hour at 120 °C and in the microwave for 10 minutes at the highest level. Moisten the substrate well beforehand! Newly purchased indoor plants should first be isolated so that you can observe them and detect any pest infestation in good time.
combat
Fungus gnats can be fought and repelled in the following ways:
- Hanging yellow boards
- set up carnivorous plants such as sundew and butterwort
- Cultivate affected plants drier / water less often
- Use mineral plant substrates instead of humus soil
Many popular houseplants can also be kept well in hydroponics, pests such as black flies don't stand a chance here either. In addition, the plants are always perfectly moisturized in this way and therefore less susceptible to many pests.
spider mites
Spider mites are also referred to as red spiders because of their often reddish-brown or orange coloration, but there are also greenish colored specimens. These pests are very common on almost all indoor plants, preferring a dry and warm environment. The arachnids feel really comfortable in winter heating air, which is why an infestation mainly occurs in late winter / early spring. But the plague can also occur in the hot summer months.
symptoms
These insects also belong to the pests that suck plant sap and cause a correspondingly typical pattern of damage:
- numerous small leaf spots, mottled leaves
- Spots initially appear yellowish-white to silvery
- later grey-brown discoloration, leaf dries up and falls off
- with severe infestation, fine, white webs, especially on leaf axils and leaf edges
Spider mites are proving to be a major threat to loganberries.
You can identify a suspected red spider infestation by wiping the underside of one or more leaves with a white cloth. If reddish or yellowish streaks or spots appear on it, it is spider mites.
control and prevention
Spider mites love dryness and can therefore be easily driven away with these measures:
- Rinse affected plant with lukewarm water
- Repeat treatment several times on different days
- Increase humidity, e.g. B. by indoor fountains
- Spray plants regularly with water as a precaution (only for plants that tolerate it!)
- Use a plant sauna if the infestation is severe
In the plant sauna, you destroy the pests with an extremely high level of humidity. Water the affected plant well, put it in a transparent plastic bag and tie it up. Leave the plant like this for a few days, after which the insects will have died. But be careful: Not all plants tolerate this procedure, some start to rot very quickly.
Tip: You can also use predatory mites against spider mites, which you can purchase in appropriate portion sizes from specialist retailers.
Thrips / Blister Feet
Thrips are small, black insect pests that only grow between one and three millimeters in size. They are also known under the names Thunderbirds or Bubble Feet. They multiply rapidly, especially in warm and dry air, which is why an infestation occurs mainly during the winter heating period.
symptoms
The damage caused by thrips is very similar to that of spider mites.
control and prevention
The pests can be controlled by the following measures:
- rinse infested plants
- then isolate to prevent spread
- increase humidity
- choose a cooler location
- Hang up or attach yellow boards or stickers
Here, too, special predatory mites, which you can purchase in specialist shops, help with a heavy infestation.
white flies
Whiteflies are commonly found on houseplants. The insects, which are only about two to three millimeters in size, are not really flies, but lice that suck plant sap. The pests originally come from the tropics and are therefore only found in warm to hot temperatures. The whitefly feels particularly comfortable at temperatures of more than 23 °C and a high humidity of 70 percent or more.
symptoms
Whiteflies can often be recognized by the fact that they fly up en masse whenever there is a disturbance. Otherwise, they perch on the undersides of leaves, side by side, and are easily identified by their imbricated wings. These lice suck the plant sap and therefore cause the following symptoms in the infested plants:
- Plants lose vitality
- seem powerless, grow poorly
- affected leaves are mottled at first
- eventually die and fall off
- sticky honeydew on the leaves and underneath the plant
- Possibly colonized by sooty mold (black coating)
control and prevention
Unfortunately, rinsing or showering off the infested plants does not make much sense, as the flies fly up immediately. Therefore, isolate the plant in question to prevent it from spreading and hang up yellow boards or stickers. You should also keep the plant as cool as possible, as the tropical insect does not tolerate cool temperatures. Ichneumon wasps also help against an infestation.
Mealybugs and mealybugs
Mealybugs or mealybugs are a subspecies of scale insects. In contrast to these, however, these lice do not form a solid shield, but are protected by a white, waxy substance. This makes the pests look like small cotton balls. The animals appear mainly in dry air.
symptoms
The symptoms are reminiscent of those of scale insects, except that instead of the brownish shields, there are white cotton balls on the underside of the leaves.
control and prevention
The same applies here: Isolate infested plants and increase the humidity. Otherwise, a biological preparation based on neem helps very well against mealybugs and mealybugs. This is a natural insecticide obtained from the fruits of the Indian neem tree.