Whiteflies: how to identify, prevent & get rid of them

Whether on houseplants or in the garden – whiteflies can be very annoying. Find out how to get rid of whiteflies using household remedies as well as natural methods in this article.

The term “whitefly” is a trivial name for various insects from the Aleyrodidae family. Like aphids and scale insects, whiteflies belong to the Sternorrhyncha family. The two most common pests in hobby gardens are the cabbage whitefly (Aleyrodes proletella) and the greenhouse whitefly (Trialeurodes vaporariorum) which have a similar appearance and life cycle. But there are also some differences, which will be discussed in the following.

Whitefly: information and characteristics

Whiteflies are small flies, about two millimetres in size, covered with a white powder. Due to their rapid reproduction they are among other pests like aphids a great fear of gardeners. From the egg through several larval stages to the adult fly, it only takes several weeks for these insects to fully develop, especially in warm temperatures. Their rapid reproduction causes several generations of whiteflies to form during the vegetation period, laying 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 causes the leaves of the infested plant to stick together. This in turn provides a perfect breeding ground for fungi, especially sooty mould, which further exacerbates the problem. Fungi on leaves inhibit the photosynthesis of the plant.

What is more, the whitefly can also be a carrier of various plant viruses if the previous host plant for example was an infested wildflower. Diseases caused by a virus cannot be cured. The degree of damage can range from flawing the plant’s beauty to ruining it completely.

Often it is not the whitefly infestation itself that poses the biggest problem. It is rather the sooty mould or induced plant diseases that cause the most damage. The main season for whitefly infestation is late summer to autumn, as large populations are already at work at that time. If temperatures are high enough in early summer, a whitefly season will also be brought forward.

Whiteflies: identification and symptoms

To discover whiteflies, inspect the bottom of the leaves of potential host plants. Both adult flies and larvae as well as the eggs hide beneath the leaves. The ring shape in which the white to yellow eggs are laid is a typical feature of whitefly infestation. After hatching, the larvae – whitish to yellow-green-brownish grubs move around. In later larval stages they settle down and stay in one spot. The underside of a leaf 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 an arched shape.

Whiteflies are covered with waxy white dust. Therefore, you can identify a whitefly infestation by the white dust on parts of the plant, the soil around the plant and, of course, by the small white insects. A sticky coating indicates honeydew excretion – if it is black, sooty mould has sadly already settled onto 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

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 infest 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 the whiteflies to disappear by next year. Adult whiteflies might also find other cruciferous plants (Brassicaceae) for overwintering, such as winter oilseed rape.

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.

On houseplants

The greenhouse whitefly particularly likes to infest houseplants. The evenly warm temperatures and lack of predators provide the whitefly 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 been asking yourself how to get rid of whiteflies on plants, this section is for you. A heavy whitefly infestation can cause severe damage to your painstakingly planted and tended vegetables. All of the whitefly’s unfortunate side-effects be it the lack of plant sap, the spread of sooty mould or the transmission of plant viruses can only be reduced by whitefly treatment.

How to treat whiteflies naturally

Whiteflies are an annoying plant parasite, but synthetic insecticides 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 environment friendly and extremely effective way of treatment is to use neem oil for whiteflies. Neem-based products are based on neem tree oil. Neem oil contains the active ingredient azadirachtin, which is absorbed by the insects when they suck on the plant sap. Neem products prevent the larvae of whiteflies from developing and thus gradually reducing the whitefly population.

Natural control of whiteflies in summary:

• Mix neem product with water according to packaging instructions
• Apply emulsion onto the affected plant with a spray bottle
• Young shoots are also protected by the systemic effect and do not need to be treated afterwards
• Whiteflies should be eliminated by no more than two weeks after first application

Agents based on rapeseed oil or orange oil are another possibility to control whiteflies. The oil prevents sufficient oxygen supply of the insects and causes them to die. Rapeseed oil products also destroy the eggs of the pests. However, some plant leaves do not tolerate those products due to their thin walled cell structure.

Home remedies

If you are only dealing with a slight infestation, you can also use home remedies. A frequently used household remedy against whiteflies is 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 hack to treat whiteflies are soap suds. A soap solution of 30 grams of potash soap or 200 millilitres of liquid soap on one litre of water can also be applied onto 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, chemicals and pesticides are also an option for whitefly control. 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. Pesticides against whiteflies can also contain vegetable pyrethrins. These active ingredients are unfortunately also harmful to beneficial insects. Stay away from chemical products if you want to keep the environment safe.

Another environment friendly method in case of less severe infestation are yellow glue traps. These can be placed near infested plants. They attract whiteflies due to their yellow colour and the pests stick to the traps. Yellow sticky traps are suitable for indoor application or greenhouses, as the yellow colour can also attract bees and other pollinators. They are in general a great solution for early detection of whiteflies more than for control. They work best when used in combination with other natural or DIY methods as 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 and detection

Whiteflies: prevention

Prevention is better than cure. You can prevent whitefly infestation with a few tricks. Whiteflies for example are repelled by the smell of some plants. Thyme (Thymus), basil (Ocimum basilicum), sage (Salvia officinalis) and marigold (Tagetes) are great to use for whitefly prevention. You can set plants prone to infestation whitefly-repelling herbs. You can also use wild herbs, such as 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 protect your garden.

Both in the open field and in your living space, an optimal supply of nutrients for 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 using products specifically adapted to the needs of your plant. Specific 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. Plantura fertilisers enable you to fertilise your plants according to their needs out in the open and at home.

A bright and well-ventilated location, especially looking at indoor plants, can also prevent whitefly infestation. Conditions that help your plants grow vigorously and strongly increase their resistance to pests and diseases.

How to prevent whiteflies in summary:

• Grow strong scented companion plants
• Promote beneficial insects in the garden
• Supply the plants with nutrients using organic fertilisers
• Grow houseplants in a bright and well-ventilated area

You can find further natural remedies against annoying plant pests in our shop.