One of the most common pests of citrus trees in the home garden is whiteflies. Whiteflies are not actually flies but small white moths and can be a serious problem in the US and Australia. The tiny adult is about 2.5mm (0.10 inches) long and is a sucking insect usually found on the under-surface of citrus leaves. They multiply quickly in warm conditions to reach huge numbers on one tree. Luckily they don’t do permanent damage to trees however they do infest young leaves and flushes, sucking the sap from these tissues. No leaf or shoot distortion occurs but they produce honeydew (sugary secretions) which becomes a food source for sooty mould fungus. The mould interferes with photosynthesis, leaving the citrus trees weakened and unable to produce a normal yield of fruit.
Whiteflies are best controlled by beneficial insects, light oil sprays, naturally occurring fungi and pruning. Natural predators of whitefly include damsel bugs, spiders, lacewings, mirid bugs, hoverflies, ground beetles and small birds. The adults and larvae of some ladybirds also feed on whiteflies. Whiteflies are strongly attracted to the yellow colour of sticky traps so hang these above or close to the top of the plants. You can also handpick and destroy older leaves to remove young whitefly stages.
Friendly orange-red fungi parasitizes immature whiteflies, so don’t be alarmed when you see these ‘good guys’ on the bottom leaf surface. Pruning to open the tree canopy and allow wind ventiliation can also help.
You will find full details about whiteflies and great advice and photos on recognising and correcting nutrient deficiencies, pest and diseases and problems of citrus trees in Grow Citrus: The Insiders Secrets to Growing Great Citrus