Whiteflies: Proven methods to combat the scourge of greenhouses

Are tiny white flies fluttering around your plants? Then you're dealing with whiteflies. They are common insect pests found on plants grown in greenhouses, indoors and outdoors. Whiteflies are not the most dangerous insects, but they suck sap from leaves, transmit diseases, and it's a good idea to get rid of them quickly. Fortunately it's not very difficult. We'll tell you how!

What are whiteflies and why are they so dangerous?

Whiteflies (Aleyrodidae) are small insects related to aphids that feed by sucking plant sap. At first glance these tiny white flies may seem harmless, but they can cause considerable damage to plants. Besides weakening the plant by feeding, they also excrete sticky honeydew — a sugary substance that settles on leaves and promotes fungal growth. These fungi reduce the leaves' ability to photosynthesize and further weaken the plants. Whiteflies are also vectors of various viral diseases that spread very quickly among plants, especially in a greenhouse, grow box or indoor grow room. If you allow whiteflies to multiply, you can easily lose the entire crop.

How to tell you are dealing with whiteflies

Noticing whiteflies is not difficult. Adults look like small white flies and measure about 1–2 millimeters. You will usually see them fluttering around the plants, but most live on the underside of leaves where they feed. To check how serious the infestation is, try gently shaking the plants and see how many fly out from under the leaves. Other signs of whitefly infestation include:

• White spots on leaves: Whiteflies secrete a waxy white substance that leaves marks on leaves and promotes fungal growth.
• Damaged leaves: Infested plants have wilted leaves dotted with pale speckles.
• Whitefly eggs: You can find whitefly eggs on the underside of leaves in a characteristic circular arrangement.

Natural methods to fight whiteflies

If you've noticed whiteflies around your plants, try proven natural methods before reaching for chemicals. They are gentle on the environment and often very effective:

• Yellow sticky cards: Whiteflies are attracted to yellow, and if you place yellow sticky traps around infested plants, you can easily catch the adults. Replace sticky cards regularly.
• Biological control: Parasitic wasps (formosa, E. eretmocerus), predatory mites (Amblyseius swirskii) and entomopathogenic fungi (bassiana, I. fumosorosea) are very effective against whiteflies.
• Bio spray for whiteflies: Try insecticidal sprays containing essential oils (Rock Effect) and other biodegradable products (e.g. CannaCure, BioBizz Leaf Coat, BioNova NovaFoliar, Botano Health).
• Preventive sprays against whiteflies: Preventing infestation is easier than removing it. Therefore, regularly treat even healthy plants with preventive protective sprays that protect them from pests and pathogens and improve their vitality.

Products against whiteflies

If you fail to eliminate whiteflies with natural means, more powerful methods are next. Even then you can choose between ecological sprays against whiteflies and chemical insecticides. When using them on plants intended for consumption, be cautious. These products require a withholding period and can harm your health.

• Systemic insecticides: Sprays containing the active ingredient acetamiprid (Mospilan) work very well against whiteflies. They have a long-lasting effect and act on all developmental stages of whiteflies from larvae to adults.
• Sprays for whiteflies: You can also try sprays containing azadirachtin or sprays targeted to eliminate whiteflies.
• Home spray for whiteflies: A neem oil spray is also very effective against whiteflies. Simply mix 5 milliliters of NeemAzal with 1 liter of warm water and a drop of liquid soap. Apply this mixture first twice with a three-day interval and then continue applications until the whiteflies are eliminated. Note, neem oil has a strong taste and smell and is not suitable for application on medicinal plants in full bloom.

You may be interested in: How to deal with spider mites

For more advice on how to fight pests and other tips and tricks for indoor and outdoor growers visit our Higarden blog.