Whitefly on Indoor Herbs
Answered by: Richters Staff

Bill Calder asks
How can I prevent whitefly on houseplant herbs such as basil etc.?

Contrary to a popular misconception, herbs are not immune to pests. Some "experts" have suggested that herbs repel pests and so are not bothered by them.

Herbs are every bit as susceptible to pests as other house plants. Whiteflies, among others, attack most members of the mint family – which includes catnip, marjoram, oregano, rosemary, sage, thyme, and mint – as well as many other herbs. Whiteflies do not bother succulent herbs like aloe vera or hairy herbs like woolly thyme and dittany of crete.

The easiest way to prevent whiteflies on indoor herbs is to make sure plants are clean before bringing them indoors. This is easier said than done in many cases because virtually *every* commercially or privately grown plant is a possible haven for whitefly eggs. Just a few can develop into a nasty problem. The eggs are laid on the undersides of leaves, and are too small to be seen clearly by the naked eye. A single adult female can lay up to 400 eggs which will develop into adults 4-5 weeks later.

If you start plants from seeds then you can avoid whiteflies as long as you do not introduce infested plants or expose plants to outdoors (via open windows and doors). But whiteflies seem to find one way or another to infest plants, so it pays to always be on the lookout for them. If you catch an infestation early it is easy to destroy completely. If a whitefly infestation takes hold – say 20-30 whiteflies per plant – it is difficult to get rid of them.

We use Safer’s Insecticidal Soap and Safer’s Trounce products. These are safe to use on edible plants. Trounce is the same as Insecticidal Soap with the addition of pyrethrum, a natural insecticide derived from the pyrethrum flower. Pyrethrum improves the kill rate.

When using insecticides like soap and pyrethrum it is essential to cover all surfaces with the spray. These are contact insecticides. Unlike many chemical sprays that leave residues, they only work if insects get drenched with spray. Whiteflies are rather clever and tend to live on the undersides of leaves which makes getting a good coverage on all surfaces difficult. But you must persist, and you must repeat sprayings every 3-4 days for several weeks until the whiteflies are completely eliminated. It is a good idea to continue spraying for a few weeks past the last signs of pests to make sure stray eggs don’t hatch and repopulate your plants.

Another trick is to use yellow sticky traps that neatly mount in wire holders you stick in pots. The yellow colour attracts whiteflies and they get stuck and die. These will help catch a few of the whiteflies, but more importantly, they will help you to detect the presence of whiteflies at an early stage of an infestation.

Persistence is crucial. A single spraying will not eliminate pests – it rarely works like that. With natural pest controls the need for repeat sprayings is a given.

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