Trialeurodes vaporariorum - when young, they appear as small (1½mm long), scaly creatures on the underside of leaves. These scales protect them from many insecticides. The more adult whitefly look like tiny white moths, and they will make short circular flights when disturbed. They are transparent to opaque and vary in colour from creamy white through to brown.

How to Treat Whitefly

If the whitefly are attacking an outside plant then it is unlikely to be serious. Keep the plant healthy and it should shrug off the attack by itself. I you want to treat an outside plant then spray with soapy water as described below. It is also effective to use systemic pesticides (see below).

If the whitefly are attacking plants in a greenhouse then it can be serious if left to run its own course. The best course of action is to act in advance each season. Expect the whitefly attack from April onwards and act before it becomes severe. The steps for this are described below as well as how to control whitefly when the attack is more severe.

Whitefly Greenhouse Control - Act in Advance

Many whitefly are now resistant to pesticides so the best course of action is biological control combined with fly-catching sheets. The first stage in the life of whitefly is as nymphs which attach themselves to the underside of leaves. Theses nymphs can be biologically controlled by parasitic wasps. The second stage of the whitefly life is when the nymphs mature and emerge as flying whitefly. Any that get to this stage can be controlled by fly-catching sheets.

Whitefly Greenhouse Control - Biological

In late March or early April order online the parasitic wasp (encarsia formosa). If you Google the Latin name (encarsia formosa), several suppliers will appear. Our recommended supplier of this parasitic wasp can be found by clicking here. The wasps will eat the whitefly nymphs.

The wasps work best when they are let loose before the whitefly population is moderate. Once they have been introduced, don't spray the tomatoes with pesticides because that will kill the wasps.

Whitefly Greenhouse Control - Fly-Catching Sheets

In mid-April, buy some fly-catching sheets and hang them near your greenhouse plants. Any nymphs which are missed by the parasitic wasps above will turn into whitefly. Most of these should be caught by the fly-catching sheets.

Whitefly Greenhouse Control - Chemical

Many of the chemicals for killing whitefly, including the most effective ones, are systemic. They work because the plant absorbs the chemicals and when the whitefly feed on the leaves, they are poisoned by those chemicals. I'm not really sure that I would want to eat fruit / produce from a plant which has absorbed chemicals that kill whitefly! The biological and fly-catching sheets seem far safer.