Spring and summer are glorious times of the year, but they can bring unwelcome pests to your garden – including black citrus aphids.
Liam Kemp, an Airtasker Horticulturist and owner of Kempscapes, emphasises the significance of tackling aphids during these seasons. He says, “In spring and summer, aphids are much more prevalent as they feed on newer and more tender growth, so this is the most important time to get on top of them, especially since they produce multiple generations per year.”
What do black citrus aphids look like?
These small sap-sucking insects are typically black but can occasionally be dark brown or green, and measure just 1 to 3 millimetres. They have a specialised mouthpart called a stylet to pierce and extract sap from leaves, green shoots, and flowers. Some aphids have wings, an adaptation to overcrowding or environmental changes, which means they can migrate to new plants.
There are actually two main species of black aphids found on citrus in Australia: Toxoptera aurantii and Toxoptera citricida (sometimes called brown citrus aphid).
According to the NSW Department of Primary Industries and Regional Development (NSW DPI) aphids can be visible on new shoots and young leaves, with sticky honeydew and sooty mould growth also potentially indicating their presence on citrus trees.
Do black aphids bite?
Black aphids do not bite humans. But black citrus aphids (and other aphids) do suck sap out of your plants and can also transmit viruses to them, so they are more of a threat to your garden than your skin.
Aphid lifecycle
The life cycle of black aphids typically involves a female aphid depositing eggs on the plant’s surface. These hatch into nymphs that undergo several stages, and mature into winged or wingless adults.
Rapid asexual reproduction, especially during spring and summer, allows for a swift increase in aphid populations.
Do aphids affect lemon trees?
There are several varieties of aphids that affect lemon trees and other citrus trees. As well as black citrus aphids, this includes the melon aphid (Aphis gossypii) and spiraea aphid (Aphis spiraecola), according to the NSW DPI.
How to get rid of black citrus aphids
Liam recommends using Yates Nature’s Way Citrus and Ornamental Spray, and neem oil to effectively control black aphids on citrus trees.
“Both are organic and safe to use on citrus with black aphids and have fairly good results,” he says.
How to treat a citrus tree with black aphids
Act swiftly at the first sight of black aphids on your citrus tree. Apply the citrus spray or neem oil immediately, repeating every 5 to 14 days until the infestation subsides.
Liam emphasises the importance of enhancing your tree’s health to fortify its defences against pests by “clearing vegetation around the base of the tree and feeding with an organic fertiliser high in potassium as the healthier the tree, the better it can fight diseases.”
And for a natural touch, Liam points out that lady beetles and green lacewings are eager allies in munching on any aphids residing in your garden.
Natural aphid enemies are also available for online orders, delivered conveniently in plastic containers. Release these beneficial insects onto your plants for a biological pest control method. You can explore different options at Bugs for Bugs.
Does vinegar kill black aphids?
As aphids are soft-bodied insects, it’s possible vinegar may harm or kill them. But there is also a risk of further damaging the leaves and new shoots by applying undiluted vinegar.
An alternative, natural way to kill aphids is to spray the affected leaves and shoots with an organic garlic or chilli spray, according to the WA Department of Primary Industries and Regional Development. You could also physically remove and squash the aphids, or use a jet of water.
How to prevent a black aphid infestation on citrus trees
Prevention is always better than a cure, especially with black aphids on citrus trees. Here are Liam Kemp’s top three tips to prevent an infestation:
- Pre-planting: Before introducing new plants, thoroughly inspect your garden for existing citrus plants affected by black aphids. Address any issues to ensure a clean environment for new additions.
- Mindful fertilisation: Exercise caution with nitrogen-rich fertilisers. Over-fertilisation with nitrogen can inadvertently attract aphids, rendering the tree more susceptible. Strike a balance in fertilising practices to maintain a healthy citrus orchard.
- Strategic pruning: Prune the inner branches of the tree as aphids favour this area. This targeted pruning disrupts the aphids’ preferred habitat and makes the tree less desirable to them.
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