The whitefly are small hemipterans (true bugs) that typically feed on the undersides of plant leaves. They are a tiny, white winged, moth-like insect, and are relatively easy to see on infested plants. They produce a sugary substance called honeydew on leaves, stems and fruit.
Whitefly are a common pest, but those that affect outdoor crops such as cabbages, rhododendrons and even viburnum are not the same species as those annoying clouds of insects that waft around the greenhouse. Both are called whiteflies, but they are specific to their host plants and require different modes of control.
A noticeable white, waxy substance saturating the leaves is a sure sign of infestation. The female whitefly can lay up to 200 eggs at a time. They will lay eggs on plants, which hatch and then the young start sucking the sap out of the host plant causing stunted growth, and if left untreated, will cause destruction. If you disturb a plant that has a whitefly infestation, you will see a cloud of the insects flying up off the plant.
There are two types of damage which whitefly can cause to a plant; firstly, direct damage which is caused by the sucking of juices causing leaf damage. Secondly is indirect damage, and this is caused by diseases, which are transferred to the plant from the insect’s mouthparts. A severe infestation can cause wilting and a loss of energy for the plant.
Greenhouse whiteflies are notoriously difficult to kill, as they have become resistant to certain chemicals. Whitefly will be attacked by other insects such as spiders, ladybirds and hoverfly. If you are considering introducing an insect to assist with your problem, ensure you do your research as you could end up creating an even bigger insect problem. Planting French and Mexican marigolds tend to repel whiteflies, although this is not a perfect solution for an existing problem, and is more effective at the first signs of an attack.
Other prevention methods are:
In the garden;
- Keep plants in good health;
- Avoid overfeeding with high nitrogen fertilisers that encourage soft, sappy growth;
- Cover young cabbage plants with horticultural fleece to keep flying insects at bay.
In the greenhouse;
- Hang yellow sticky traps to catch passing bugs. Growing Success Whitefly Traps, these attract and trap whitefly, and are pesticide free and environmentally friendly. These can also be used for monitoring and control of whitefly.
Controlling the problem
Use Resolva Bug Killer to treat whitefly at the first signs of infestation before the population gets a hold. Heavy infestations can also be treated with this product and it can be used on edibles, roses and flowers in gardens and greenhouses. Please note this product can’t be used to prevent whitefly, as it has no residual effect – in other words the pest needs to be there in order to control it.
Always read the label. Use pesticides safely.