Common houseplant pests and treatment
Even the most doting of houseplant lovers is unfortunately likely to experience pests on their beloved collection at some point, so here is a rundown of the most common houseplant pests with tried and tested treatments.
These are probably the most common houseplant pest. They are small dark coloured flies, often confused with fruit flies which are slightly lighter brown in colour. The gnats are drawn to damp conditions and have a larvae stage which live in the soil.
Fungus Gnat Damage
The gnats themselves do little damage but are an annoyance. The larvae can attack the fine roots of plants eventually causing the plant to weaken and causing yellowing leaves.
Fungus gnat treatment
There are a number of methods to try listed below, either in conjunction with each other or independent from each other. All are natural and many require just a few items you will likely have at home.
Introduce a Nematode (a living organism that is a natural predator). Fungus gnat nematodes should be mixed with water and applied to the affected plants as per suppliers instructions. The nematodes will kill the larvae of the fungus gnat.
Repot the plant in new soil with the aim of removing larvae.
Add a good layer of cinnamon to the soil which acts as a natural fungicide killing the fungus that the larvae feed on.
Place a cup of beer or apple cider vinegar mixed with a few drops of washing up liquid next to the plants to attract and then drown the gnats.
Cover the soil with a grit, sand or small pebbles. We love Shell On Earth’s crushed whelk shells for this.
Place yellow sticky traps around the plant to attract and kill the gnats.
Place a carnivorous plant such as Pinguicula (Butterwort) next to the affected plants to attract and kill the gnats.
Fungus gnat prevention
Water from the bottom of the plant to avoid over watering and to prevent the soil from being damp for extended periods. Allow the top of the soil to dry out between waterings.
The much maligned mealy bugs are often brought into the house from an infected plant. They do not travel far so strict quarantining of affected plants along with the treatment methods below can be really successful.
Mealy Bug Damage
The bugs are visible to the eye, appearing as white fluff. They are often found in flowers, stem joints and leaves. They suck the plant’s sap and the excrement produced is a sticky substance called honeydew which becomes mouldy. Sucking of sap weakens the plant and in long-term infestations the leaves will become yellow, eventually drop off and the plant can die.
Mealy Bug Treatment
Remove the visible bugs as quickly as possible using a cloth and horticultural soap. Be sure to check under leaves and stems, and in any crevives on cacti and succulents.
It is always a good idea to isolate affected plants to limit the pest spreading to other plants.
Mealy bug prevention
You can also use the horticultural soap as a preventative method on non-affected plants. Clean leaves and stems using the horticultual soap every couple of weeks.
Thrips are known for being one of the trickiest blighters to eradicate and are easily spread from one plant to another. The adult thrips are 1-2mm long winged insects (thunderflies) however you may also spot the wingless larvae which are light yellow in colour. Persistance is key to battling these.
Thrips feed by sucking sap which causes a discolouration on the upper side of the leaf, which can often appear as silvery streaks. You may also spot small brown specks which are excrement. The sucking of sap will eventually weaken the plant. Damage to new shoots can cause distorted growth.
Remove any infected areas of the plant, then hose the plant to wash away as many of the pests as possible (try not to let the water run into the soil at the base of the plant).
At the first sign of thrips (and as a preventative measure) we recommend using a Slow release sachet containing Amblyseius mites. They will attack the larvae and pupae stages of Thrips, stopping an outbreak.
For a serious infestation turn to another natural predator; Orius bugs within Orius Thrips Killer. This mixture of 500 adults and nymphs will attack all stages of Thrips, it is one of the only biological control agents that is able to kill adult thrips.
Carry out regular checks on your plants for thrips, their larvea and damage. New plants can be quarantined for extra safety. Clean leaves and stems using horticultural soap every couple of weeks.
These are minuscule spiders whose damage can eventually kill a plant. They can be tricky to spot until an infestation is serious so it is worth keeping a close eye on your plants and looking out for tell-tale signs. It’s worth noting that Calathea are particularly prone to spider mites.
Spider Mite Damage
Spider mite damage will appear as yellow or brown mottling on the upper side of a leaf, caused by piercing of the underside of the leaf in order for the pests to suck the sap. In heavily infested plants you will spot webs and the mites themselves. Serious infestations can cause leaves to drop and the plant to die.
Spider mite treatment
Remove any heavily infected areas of the plant. Hose or wipe the plant to remove as many of the pests as possible and then apply horticultural soap. This can also be used as a preventative measure.
Predatory mites can be used to treat and prevent large outbreaks. The slow Release Sachets of Amblyseius Andersoni mites contain a breeding colony of mites that crawl out slowly over a period of 4-6 weeks stopping an infestation from taking hold.
Spider Mite Prevention
Carry out regular checks on your plants for spidermites and damage. New plants can be quarantined for extra safety. Clean leaves and stems using the horticultural soap every couple of weeks.
Scale are sap sucking insects that are relatively easy to identify due to their appearance, they are generally 1mm to 1cm diameter, round, brown 'shell' or bump. They are a sap sucking insect and secrete a sticky honeydew. Due to their 'armoured' backs, sprays don't often have an effect on Scale insects.
Scale insect damage
As the insect sucks the sap of the plant, it will weaken and damage the plant, however it may be the scale insects themselves that you spot first.
Remove any heavily infected areas of the plant. Scale insects can be removed individually by wiping them off, however for a quicker solution choose a natural predator; Scale control nematodes. The nematodes 'swim' on the film of water allowing them to enter the scale insect and kill them.
Carry out regular checks on your plants for scale insects and damage. New plants can be quarantined for extra safety. Clean leaves and stems using the horticultural soap every couple of weeks.
It is unfair to have Springtails mentioned in a blog about pests as they actually cause no harm to our houseplants at all. Nevertheless they are often mistaken for something more damaging so it is useful to be able to identify them.
Springtails are small wingless, 6 legged creatures. They grow up to 6mm and are able to jump when disturbed. They are no longer classed as insects and are instead known as Hexapods.
You are likely to spot Springtails crawling around on top of soil once you have watered, or in the soil when you are repotting.
Springtails live in soil and feed on decaying vegetation and microbes, hence why they don’t cause damage to our houseplants - lucky for us they don’t feed on living vegetation.
We hope this has proved useful and encouraged you to turn to natural preventative and treatment measures rather than resulting to a bottle of chemical pest spray.