Our Pest Control Expert, Julian Ives, has spent many years advising commercial growers and gardeners on the subject of safe and efficient natural pest control treatments.

Here he shares his experience on the problems Whitefly can cause in the garden and how to get the best from the Whitefly Control we supply...

Using Whitefly Control
Encarsia formosa is one of the oldest forms of biological control and is used extensively by professional growers of crops such as tomatoes and cucumbers.

This tiny parasitic wasp injects its egg into the whitefly larvae. This egg then develops into an adult Encarsia formosa and stops the whitefly developing. The parasitized larvae turn black eventually, which gives a clear indication of the activity of this parasite. However it will not turn black for up to two weeks, so patience is required in monitoring the progress of this biological control.

The Encarsia formosa are supplied as parasitized scale stuck to cards. These cards should be separated and hung on plants. Place the cards out of direct sunlight. Over a few days the Encarsia formosa will emerge from the cards and fly around looking for whitefly scale to parasitize.

They require a minimum temperature of 18.c to be active and only fly in the day. Low temperatures and short days will reduce their activity. The most effective way to use this product is by regular introductions and a programme of whitefly control will help with this.

 If you are removing leaves from tomato plants, ensure you leave the leaves on the floor for a week, as parasitized whitefly can be removed from the greenhouse if you take them out too early. The Encarsia tend to lay their eggs on the lower leaves. Also remove any yellow sticky traps when using this product.

Appearance and Lifecycle
There are several species of whitefly that gardeners may encounter. The most common is glasshouse whitefly Trialeurodes vaporariorum found on greenhouse grown plants. Other species include the Cabbage whitefly, Strawberry whitefly and the tobacco whitefly. The glasshouse whitefly lays its eggs on the underside of leaves. These eggs hatch into oval shaped larvae, which eventually turn into a pupa before the adult whitefly emerges. At a temperature of 20.c the life cycle from egg to adult is about 30 days. The number of eggs is very influenced by temperature, with higher temperatures increasing the egg laying significantly. Whitefly can overwinter on host plants in greenhouses either as eggs or adults.

Symptoms and Damage
The first sign of whitefly is often observed when plants are disturbed and adult whitefly up from the plant. Whitefly is sap feeding insects. They consume large amounts of sap. This stunts the growth of plants and leads to plants wilting and leaves dropping off. For fruit bearing plants this also leads to a reduction in yield. Much of the sap extracted from the plant is also returned to the surface of the pant as honeydew by the whitefly. This sticky substance attracts moulds, which turn the honeydew black and can cover leaves and fruit. Some whitefly species also spread pant viruses when feeding on plants.

Natural Choice Treatments
A combination of Natural Choice solutions can be used to control and reduce whitefly damage. First make sure yellow sticky traps are hanging in glasshouses in the winter and early spring. Any early whitefly can be spot sprayed with a safe spray like Savona Insect Killer Spray  and then when temperatures rise, biological control can be introduced in the form of the tiny parasitic wasp, Encarsia formosa.