How To Combat Whitefly

Insecticides are the most-used weapon against whitefly infestation in houseplants. But because the eggs and larvae resist insecticide attack, you will need to spray every 2-3 days for a week or two to ensure that the whole colony is treated.

If there are only a few insects present, it may be sufficient to spray the plant with a mixture of soapy water and methylated spirit.

whitefly-damage

Otherwise, choose a spray containing pirimiphosmethyl and pyrethrum. Make sure you spray the underside of the leaves.

If you can take your plants to a greenhouse for treatment, you can use a whitefly smoke canister. This is a highly effective killer of the pest on all parts of the plant. Remember when you use chemical sprays to follow the manufacturer’s instructions carefully.

What Are Whiteflies?

whitefly-feeding

Strictly, they are not flies at all, but a form of wood louse. ‘Flour lice’ is one common name for them, since their whiteness suggests they have been dusted with flour. These very small insects are closely related to greenflies (aphids) and scale insects.

Active indoors and out, whitefly are specially fond of fuchsias, geraniums, hibiscus, impatiens and poinsettias among popular house plants. The battle against this pest is winnable nowdays, but treatment should be regular and swift to control them.

Life cycle on the plant

Whitefly live on our plants throughout their three life-stages. During the first stage, whitefly lay eggs which appear on the underside of leaves as white patches arranged in regular curves. Each female can produce 100-200 eggs at a time.

whitefly-eggs

The eggs themselves do no damage, but they hatch in two weeks (sooner if the weather is warmer) into larvae that immediately start feeding on the host plant. Then, between 1030 days later, the larvae turn into fully-fledged adults and the cycle starts again.

It is the adults that do the most immediate damage,as well as laying the eggs for the next generation of whitefly.

Whitefly damage

As they feed on the plant, the larvae and adult flies do three kinds of mischief. They extract sap from leaves and shoots, weakening the plant and distorting its shape. They excrete a sticky honeydew substance that can serve as an ideal bed for the blight known as rust fungus—a sooty black mat deposit.

Whitefly lay their eggs underneath the leaves. The adult whitefly has white wings, and looks like a fly or mosquito.

The sticky honeydew discharge blocks the plant’s pores, or stomata, so making it difficult for the plant to breathe or manufacture food through the process of photosynthesis.

Preventing whitefly

Specially coated cards or spikes are available that you can insert into the potting medium. They contain insecticides that kill the whitefly (systemic insecticides). The cards are effective for 4 weeks. Follow the pack instructions but don’t use for certain plants including Maidenhair Fern and poinsettia.

Whitefly are one of the most troublesome and damaging pests on plants in the home, garden and greenhouse, but fast treatment can eradicate them effectively.

Plants to watch

  • Flowering Fuchsia
  • Slipper Flower
  • Persian Violet
  • Cineraria
  • Cymbidiurn
  • Poinsettia
  • Transvaal Daisy Regal
  • Pelargonium
  • Clog Plant
  • Busy Lizzie
  • Rosegrape
  • Mountain Sage
  • Lollipop Plant
  • Umbrella Grass
  • Coconut Palm
  • Maidenhair Fern
  • Rainbow Moss
  • Australian Bracken
  • Hare’s Foot Fern
  • Rabbit’s Foot Fern
  • Stag’s Horn Fern
  • Mother Fern

Biological Control of Whitefly

biological-control-of-whitefly

More suitable for the greenhouse than for home use, but very effective, is the use of the whitefly parasite. The larval stage of the chalcid wasp, Encarsia formosa, is available from specialist firms. The larvae parasitize the whitefly which turns black. Adult wasps emerge and lay eggs on any remaining whitefly. Use as soon as whitefly appear.

Plants like pelargonium are susceptible to whitefly.

Treatment

  • Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Spray with diluted malathion
  • Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Water soil with systemic insecticide Spray with pyrethrum-based insecticide Spray with diluted insecticide
  • Water soil with systemic insecticide Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Spray with pyrethrum-based insecticide Water soil with a systemic insecticide. Do not spray Note: Always follow manufacturer’s instructions.

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