Whiteflies: how to identify, prevent & get rid of them
The tiny whiteflies on houseplants and in the garden can be very annoying. In this article, we reveal how to get rid of whiteflies using household remedies as well as natural methods.
The term “whitefly” is a trivial name for various insects from the Aleyrodidae family. Like aphids and scale insects, whiteflies belong to the suborder Sternorrhyncha. The two most common pests in hobby gardens are the cabbage whitefly (Aleurodes proletella) and the greenhouse whitefly (Trialeurodes vaporariorum). These two species are also two of the most common whiteflies and they have a similar appearance and life cycle. But there are also some differences between them, which will be discussed in the following.
Whitefly: information & characteristics
Whiteflies are small flies, about two millimetres in size, covered with a white powder. Due to their rapid reproduction they are among those pests that are greatly feared by gardeners, just like aphids. From the egg through several larval stages to the reproduction-capable adult fly, it only takes several weeks for these insects to develop fully, especially at favourable, warm temperatures. Due to this rapid development, several generations of whiteflies are formed during the vegetation period, which lay a myriad of new eggs every day.
The larvae of whiteflies cause the most damage. They extract sap from the host plants just like aphids do. The valuable proteins are filtered out of the plant sap and a large part of the carbohydrate-rich phloem sap is excreted again in the form of honeydew. Honeydew sticks the leaves of the infested plant together. This in turn provides a perfect breeding ground for fungi, especially sooty mould, which further exacerbates the problems for the plant. By growing on leaves with honeydew, the fungi hinder the photosynthesis of the plant.
Furthermore, the whitefly can also be a carrier of various plant viruses. These plant viruses are not always very harmful to the plant: sometimes they simply reduce its beauty. Unfortunately, there is no remedy for the diseases that the whiteflies can spread.
Often it is not infestation with the whitefly and its nutrition at the plant’s expense that poses the greatest problem. It is rather the sooty mould and various plant diseases that the whiteflies spread that can cause the most damage. The main whitefly infestation periods are late summer and autumn, as large populations are already at work at this time. If summer comes earlier and is exceptionally warm, a whitefly infestation can occur sooner than expected too.
Whiteflies: identification & damage pattern
To discover whiteflies, one must inspect the underside of the leaves of potential host plants. This is because both adult flies as well as their larvae sit well hidden on the underside of the leaves. Whiteflies also lay their eggs there. A characteristic feature of the white to yellow eggs of the whitefly is that they are laid in a ring shape on the underside of the leaf. After hatching, the whitish to yellow-green-brownish larvae are at first mobile, in later larval stages they settle down and stay in one spot. The underside of the leaves often contains flies of about five millimetres in size as well as various larval stages and eggs. When the plant is touched or moved in any way, the adult insects fly away in a typical bow-like shape.
Another key characteristic of whiteflies is the white dust that envelops them. Therefore, you can tell that there is a whitefly infestation happening by the white dust on parts of plants, the soil around the plant and, of course, on the small white insects. A sticky coating indicates honeydew excretion – if it is black, sooty mould has sadly already settled on the plant, too.
You can recognise an infestation with whiteflies by the following symptoms:
- Two-millimetre large tiny white flies with wings
- Ring-shaped deposit of white to yellow eggs on the underside of the leaf
- White dust on parts of plants or the plant soil
- Sticky coating on the leaves and possibly also black sooty mould on top
Whiteflies on plants: which plants are most frequently infested with whiteflies?
Whiteflies are not picky and have a wide range of potential host plants. In the garden, most damage usually occurs to tomatoes and cabbage.
Whiteflies on cabbage
Cabbage whiteflies infests all types of cabbages. Particularly popular among whiteflies are cauliflower, broccoli, savoy cabbage, kale and Brussels sprouts. Adult flies can hibernate on Brussels sprouts and then quickly produce new populations in the following spring. Unfortunately, even removing cabbage plants over the winter does not guarantee that whiteflies will not appear next year. Adult whiteflies might also find other cruciferous plants (Brassicaceae), such as winter oilseed rape, to overwinter on them.
Whiteflies on tomatoes
Tomatoes are infested by whiteflies much more frequently in the greenhouse than in the open field. The humid and warm conditions in the greenhouse are just what whiteflies need. The pests are not picky and infest all sorts of greenhouse vegetables such as tomatoes, cucumbers and courgettes.
Whiteflies on houseplants
The greenhouse whitefly in particular likes to infest houseplants. The evenly warm temperatures and lack of predators provide the whiteflies with optimal conditions for rapid reproduction indoors. Whiteflies have a wide range of different indoor plants that they tend to target, but poinsettias (Euphorbia pulcherrima) seem to be a notably frequent victim.
How to get rid of whiteflies?
If you have long been asking yourself how to get rid of whiteflies on plants, this section is for you. A heavy infestation of the whitefly can cause severe damage to the painstakingly planted and tended vegetables in the home garden. Both the damage caused by sucking the sap of the plant, the spread of sooty mould as well as the transmission of other plant diseases can only be reduced by whitefly treatment.
How to treat whiteflies naturally
Whiteflies are an annoying plant parasite, but synthetic pesticides are not necessary to control them. Especially in the house garden and inside the flat we always recommend opting for organic and natural methods of control.
An environmentally friendly and extremely effective way of treatment is to use neem oil for whiteflies. Neem-based preparations are based on oil which comes from the seeds of neem trees. The neem oil contains the active ingredient azadirachtin, which is absorbed by the insects when they suck on the plant sap. Neem preparations prevent the larvae of whiteflies from developing and the whiteflies gradually disappear.
Natural control of whiteflies with neem in summary:
- Mix neem with water according to packaging instructions
- Apply emulsion with spray bottle onto the affected plant
- Young shoots are also protected by the systemic effect and do not need to be treated afterwards
- Whiteflies are completely eliminated after two weeks at the latest
In addition, agents based on rapeseed oil or orange oil can be used to control whiteflies. The oil prevents sufficient oxygen supply to the insects and causes them to die. Rapeseed oil preparations also destroy the eggs of the pests. However, some soft-walled plant leaves do not tolerate these preparations very well.
Home remedies against whiteflies
If you are only dealing with a slight infestation, you can also use home remedies for whiteflies on plants. A frequently used household remedy against whiteflies is nettle manure. To make nettle manure, brew 500 grams of fresh nettles with five litres of boiling water. Cool the extract and then spray it onto the infested plants several times a day using a spray bottle. Another DIY way to treat whiteflies is by using soap. A soap solution of 30 grams of potash soap or 200 millilitres of liquid soap on one litre of water can also be applied to the infested plant several times a day. We recommend covering the soil around the infested plant with a thick cloth to prevent too much soap from getting into the soil.
Other options for whitefly control
Moving on, synthetic crop protection products are also available to control whiteflies. Nevertheless, they frequently contain ingredients that are harmful to the environment, the user and animals. Active ingredients such as acetamiprid do not only harm whiteflies, but unfortunately also beneficial insects in your garden. This is why we strongly recommend using natural products and homemade remedies to treat whitefly infestations. Plant protection products against whiteflies can also contain vegetable pyrethrins. These active ingredients are sadly also harmful to beneficial insects. Please, stay away from these products to keep the environment safe.
Another environmentally friendly measure in case of less severe infestation is yellow glue traps. These can be placed near infested plants. They attract whiteflies with their yellow colour and the pests stick to the traps. However, you should only use the yellow glue traps indoors or in the greenhouse, as the yellow colour can also attract bees and other pollinators. All in all, the glue traps are great for early detection of an infestation rather than for control. On their own they are not sufficient to get an infestation under control. They are great to use in combination with other natural or DIY methods we discussed above.
How to get rid of whiteflies in summary:
- Neem oil-based products are effective and safe for the environment (be mindful of the dosage, though)
- Preparations based on rapeseed oil are suitable for hard-leaved plants
- Household remedies such as nettle manure and soap solutions can help with less severe infestation
- Yellow sticky traps are great for less severe indoor infestations
Prevention is definitely better than cure. You can prevent whitefly infestation with a few tricks. For example, whiteflies are repelled by the smell of some plants. Thyme (Thymus), basil (Ocimum basilicum), sage (Salvia officinalis) and marigold (Tagetes) are great to use in whitefly prevention. You can take advantage of this and place plants that have already been attacked specifically next to these whitefly-repelling. You can also plant flowering wild herbs, for example cow parsley (Anthriscus sylvestris), in your garden. These flowering herbs attract beneficial insects such as ichneumon flies. Ichneumon flies are natural predators of whiteflies and will help you protect your garden.
Both in the open field and in your living space, an optimal supply of nutrients to your plants is essential. Fertilising strengthens the plant and thus makes it harder for various pests to infest it. The best way to fertilise is with fertilisers that are specifically adapted to the needs of your plant. Such products will help you meet the individual nutrient requirements of your plant. Make sure that your plant is getting a good supply of potassium and calcium for stable cell walls. For this, you should fertilise with organic nitrogen fertilisers, which at best have a slow-release effect to feed the plant gradually.
A bright and well-ventilated location for your plants, especially in the living space, can also prevent whitefly infestations. Such conditions will help your plants to grow vigorously and increase their resistance to pests and diseases.
How to prevent whiteflies in summary:
- Grow strongly scented plants in the immediate vicinity
- Promote beneficial insects in the garden
- Supply nutrients to the plants with organic fertilisers
- Grow houseplants in a bright and well-ventilated area