House plants, like garden and greenhouse plants, are often bothered by a selection of tiny creatures with a taste for their sap, roots or foliage. While it is impossible to deal with each and every one of these little critters here, some of the most commonly found pests will be described separately. These common pests include:
As with problems of most kinds, prevention is usually better than cure, and there are a few things plant owners can do to minimise the risk of infestations.
New Plants and Pests
While growers do their best to keep unwanted visitors away from the plants they sell, it is a well know fact that most infestations are introduced into existing plant collections by newly purchased plants.
To prevent giving such hitchhikers a lift (or bringing a fungus/ disease infected plant home), it is best to thoroughly inspect plants before buying them.
If a plant shows one or more of the signs listed below, it is best to leave it on the shelf and look for another, trouble free plant instead. Signs of infestation/ disease - usually noticed on leaves (often on the underside), flowers and near leaf axils - include:
- Brown/ dark spots
- Egg-cases and/ or discarded shells
- Fine webbing
- Grey fuzzy mould
- Insects visible on plant
- Nibbled edges
- Powdery mildew (white dusty fungus)
- Silvery streaks
- Sticky patches of honeydew
- White, cotton-wool-like patches
Just to be on the safe side, it is also recommended to quarantine new plants for 4 to 6 weeks before placing them among existing collections. This also applies to plants that have spent the summer outside and are being returned indoors for the winter.
Routine Methods of Prevention
As pests will find all sorts of ways of getting at plants - and generally do not give a hoot whether a plant is old or new - it is obviously necessary to employ additional preventative measures. Such measures include:
- Carefully cleaning pots/ planters before using them to pot/ repot plants
- Using only sterile potting mixes (garden soil harbours all kinds of pests and diseases, and using it can prove to be disastrous)
- Promptly removing dead leaves, flowers and other debris
- Cleaning tools carefully after each use
- Bathing plants occasionally (with tepid, slightly soapy water and a soft cloth)
- Regular inspection (if necessary, using a magnifying glass)
- Immediately placing plants suspected of being infested under quarantine
- Plenty of fresh air, combined with the proper care/ feeding routine suitable for each plant, will ensure plants are healthy and more likely to resist/ overcome insect infestations.
Dealing with Infestations
Even the most careful of owners will find that occasionally, some bug or another will make it through to their plants. Panic ye not, as the saying goes, because much can be done to get rid of them effectively - although it should be said that a speedy response is of utmost importance, because the longer an infestation is left, the more the infested plant will suffer and the more likely it is that the infestation will spread to other plants.
The first move is to get the infested plant as far away from other plants as possible. If the infestation is caught early, it is often possible to simply wipe the insects off with the help of a soft, damp cloth and a little soapy water. Some pests – in particular aphids - can be removed by giving the plant a good spraying (a jet of tepid water from a fine, but forceful seedling/ spray nozzle often works wonders).
In some cases, it is best to remove infested leaves, stems and/ or flowers (discarding them safely away from any plants). Serious infestation may also require use of slightly more drastic measures, but before reaching for chemical insecticides/ pesticides, it is worth trying one or more non-chemical grower's remedies.
Both adults and larvae of soil insects may occasionally be spotted milling around on the surface of soil after watering plants. Though mostly harmless, large populations may prune roots sufficiently to cause poor growth or wilting. Drenching the soil with an insecticidal soap solution usually clears the problem, and if all else fails, systemic insecticides/ pesticides will provide the desired effect.
Ants farming aphids, mealy bugs and other pests for honeydew are generally more helpful than harmful to plants, but may cause damage by burrowing into the soil to build nests and subsequently damaging the plant's root system. Here, too, a good drenching of the soil with insecticidal soap solutions should help, as will diazinon, malathion or systemic insecticides.
Because chemical treatments often have unwanted side-effects - such as killing helpful insects or, in some cases, even the plant they are supposed to rescue, for example - most growers have over time developed their own, usually most effective remedies.
As even these remedies can affect plants in different ways (some may, for example, affect the waxy coating of succulents like Echeveria, although these effects are typically temporary), it is best to try them out on a small area of one or two plants before treating every plant in the house.
Water, Oil and Soap Solutions
A small amount of light cooking oil (in particular Canola or sunflower oil), light horticultural oil or Neem oil, shaken in one litre of lukewarm water with just a couple of drops of dish or insecticidal soap (though dish detergent should not be used) will effectively smother most, if not all of the pests if sprayed thoroughly onto every part of the suffering plant. It is necessary to spray enough of the mix onto the plant to drench it - in other words, it should run off the plant.
The bottles and nozzles used to do this will need to be cleaned thoroughly afterwards, as the solidifying soap/ oil mix will otherwise clog the nozzle up.
Hot Pepper, Citrus and Garlic Sprays
This will take a little more time and effort. Because hot pepper oils can cause serious skin irritations and are unbelievably vicious if they get into eyes, wearing gloves - and perhaps even goggles - while preparing and spraying this remedy is definitely recommended.
Ingredients include 3 hot peppers (green), 3 cloves of garlic (medium-sized) and one small onion (all of which should be pureed); 720 ml (24 fl oz, or 3 cups) of tepid water, and one tablespoon washing-up liquid. The pureed peppers, garlic and onion are spooned into a jar, to which the water and washing-up liquid are then added.
After standing for 24 hours, the pulp is strained out through cheesecloth, tights or stockings, and the liquid is transferred into a spray bottle (pump-action) to thoroughly spray infested plants.
Sucking insects will be smothered by the spray's washing-up liquid content, and chewing insects will be repelled by the scent and taste of the hot pepper, garlic and onion.
Another remedy working in a similar fashion consists of several crushed garlic cloves steeped in hot water (a few hours will do) and a couple of drops (added to the liquid after straining) of dish soap. Aphids can often be dealt with quite effectively with a spray made from the sliced rind of one lemon steeped in boiling water (600 ml/ 2.5 cups/ 1 pt).
Should all of these fail, an organic Neem oil insecticide may do the trick, although the seriousness of the infestation will determine how effective any of these remedies are. If things have been allowed to get really bad, chemical warfare may be the only remaining choice to prevent a whole collection of plants becoming infested and possibly destroyed.
Chemical Pest Control
Chemical pesticides should preferably only be used as a last resort. As some of the ingredients may be harmful to certain plants, helpful insects, pets and humans, it is vital to always read all instructions and warnings provided by manufacturers, as well as making sure the product is suitable not only for the type of pest to be dealt with, but also for the plant/s in question. If in doubt, it is better to ask for professional advice than to take the risk of killing plants.
Not every pesticide will kill every pest, and few pesticides will get rid of infestation through a single application. More often than not, repeated application is required, especially where pests with natural protection (egg cases, shells, and so on) against the effects of particular pesticides are concerned.
Treated plants should be kept under quarantine and regularly (at least once a week) checked for renewed signs of infestation. They should not be allowed to come into contact with other plants until absolutely sure the infestation has been completely removed.