How do I combat whitefly?

How do I get rid of whitefly on my houseplant?

The whitefly is an unwelcome guest that we would rather not see on our houseplants. This miniature fly is a close relative of the aphid and the mealybug, and getting them off your plants is not easy. Completely wiping out a whitefly infestation is genuinely tricky, but it is certainly not impossible! In this article you will read how to prevent whitefly and how to tackle it effectively.

What is whitefly?

The whitefly is a small insect best known for the damage it does to plants. They suck out plant sap, which slows your plant's growth. On top of that they secrete a sticky substance known as honeydew, which encourages mould and acts like a magnet on ants. That makes whitefly a double problem for your plant.

Preventing whitefly

Sadly it is almost impossible to keep whitefly away altogether, because they can be active all year round. There are still a few precautions you can take to cut the risk of an infestation:

Indoors versus outdoors: whitefly turns up most often on plants kept outdoors, especially in the summer months. Plants that stay indoors are less likely to be affected, because the flies travel from plant to plant.
Regular checks: if you have plants outdoors, check the underside of the leaves regularly, particularly when a plant is looking less healthy. That is the favourite hiding and breeding spot for whitefly.
Bringing plants inside: before you bring plants that have stood outdoors back in for the winter, inspect them thoroughly for whitefly. Carrying an infested plant indoors can spread the problem to your houseplants as well.

Types of whitefly in the Netherlands

There are several types of whitefly you can come across in the Netherlands:

Greenhouse whitefly (Trialeurodes vaporariorum)
The most common species in the Netherlands, mainly on vegetable, fruit and ornamental crops.
Tobacco whitefly (Bemisia argentifolii)
This species occurs worldwide and has no preference for a particular type of plant. It was originally found on tobacco plants, but it will settle on all sorts of crops.
Cabbage whitefly (Aleydrodes proletella)
This species mainly targets brassica crops and is often found in greenhouses. It is a relatively new strain and turns up less often on houseplants.

How whitefly spreads

Whitefly spreads quickly and efficiently. They fly easily from garden to garden or hitch a ride on the wind. That makes an infestation very hard to prevent, especially in busy gardens or where there is a large collection of plants.

Where does whitefly sit on the plant?

Whiteflies are usually found on the underside of the leaves, where they lay their eggs and their larvae develop. At first you often will not see them, because the eggs and young larvae sit on the underside of the younger leaves. As the larvae develop they can spread across the whole plant, older leaves included.

Damage caused by whitefly

The damage whitefly does is twofold:

Sap sucking: whitefly sucks plant sap out of the leaves, which weakens the plant and holds back its growth.
Honeydew and mould: whitefly produces a sticky substance called honeydew, which encourages mould. That damages the plant further and also draws in ants, which only make matters worse.

This is why it is essential to act quickly as soon as you spot whitefly.

Tackling whitefly

Whitefly can be stubborn, but there are several ways to tackle it, depending on how bad the infestation is.

Natural control: for a light infestation you can try rinsing the plant with a strong jet of cold water. This helps wash the whiteflies, eggs and larvae off the plant. Make sure you clean the underside of the leaves properly, because that is where the eggs usually sit.
Chemical control: if the infestation is too big, or the natural method is not working, you could consider a chemical treatment. Choose a product aimed specifically at whitefly and follow the instructions carefully.
Biological control: there are biological solutions too, such as bringing in the whitefly's natural enemies, for instance whitefly parasitic wasps (Encarsia formosa). These keep whitefly under control in an environmentally friendly way.

Preventive tips

Isolate: make sure any new plant you add to your collection is checked thoroughly for whitefly before you put it next to your other plants.
Healthy plants: healthy plants are less likely to develop an infestation. So give your houseplants enough light, water and nutrients.

By spotting whitefly early and acting fast, you can often save your plants from serious damage. A combination of preventive measures and control techniques is the key to keeping a garden or plant collection healthy.