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Controlling Lemon Tree Pests, Problems, and Diseases

Almost every garden in Australia has a lemon tree. It’s one of those trees that just keeps giving and giving year after year. However, lemon trees aren’t without problems, so I’m going to help you identify the more common ones and tell you how to treat them.

Let me preface this guide by saying that a healthy and well-cared-for lemon tree is less likely to attract pests and diseases than one that has been neglected.

I have a large lemon tree in my current garden that is growing in a less-than-ideal spot. However, I’ve given it a little TLC over the past couple of years and it’s now filled with lemons and has no problems with pests and diseases.

Despite my tree’s success, it’s important to remain aware of potential issues that could arise in the future.

So, let’s dive into an overview of the most common pests and diseases that could potentially affect your lemon tree.

Common lemon tree pests

Many common garden pests might be attracted to your lemon tree.

Citrus Leaf Miner

This is a tiny insect that will tunnel through the leaves of a lemon tree and the only evidence you’ll see is small silvery lines on the leaves.

citrus leaf miner | Fruit & Vegetables
Citrus leaf miner damage / Photo by Toby Hudson / Wikimedia / CC BY-SA 3.0

Eventually, the insect will curl the leaf up so that it can pupate inside. 

You’ll find this more common in young trees as mature trees will not be severely damaged.

Therefore, if you spot the damage caused by the citrus leaf miner, consider spraying your entire tree with an organic pesticide to get rid of the problem. 

If only a few leaves are affected, you can remove these and throw them into the bin so that the insect doesn’t spread to healthy leaves.

Two-spotted Mite

This is another tiny insect that feeds on the leaves and the result is that leaves will look mottled all over and will eventually turn bronze and shrivel up.

Tetranychus urticae | Fruit & Vegetables

Once again, this will be more of a problem for young trees if many of the leaves are affected.

The problem is that damaged leaves won’t be able to photosynthesise and this means that the tree won’t get all the nutrients that it needs.

If you have a severe infestation of two-spotted mites (Tetranychus urticae), consider spraying the tree with an oil-based insecticide such as white oil.

Bronze Orange Bug

These brightly coloured bugs like to feed on the young stems of lemon trees and can significantly damage new growth.

Viburnum odoratissimum Bronze Orange Bug 1 | Fruit & Vegetables

If you spot Bronze Orange Bugs on your lemon tree, you can try a few options:

  1. Hose or vacuum them off
  2. Use detergent and water to physically remove the bugs
  3. Spray the tree with an organic insecticide

Fruit Fly

Queensland gardeners will be familiar with the fruit fly and the devastation that it can cause.

I remember when I lived in Queensland myself, I was constantly battling with this pest because it will damage many different fruits, making them inedible.

The female fruit fly will lay her eggs under the skin of the fruit. When the eggs hatch, the larvae will bury themselves deep within the fruit and this causes the fruit to rot.

Fruit Fly | Fruit & Vegetables

One of the best ways to control fruit fly is to use proprietary fruit fly traps. The wick attached to these traps will attract the male of the species and traps them inside.

This can effectively interrupt the breeding cycle and the female won’t be able to lay her eggs in the fruit.

Gall Wasp

This is something I have experience with as I had two large and very mature lemon trees in my last garden that had a gall wasp problem.

However, this did not inhibit the trees from producing lots of lemons.

The gall wasp lays her eggs inside the stems and branches of the tree. This produces a swollen growth on the branch.

gall wasp nest | Fruit & Vegetables

If you look closely at this growth and notice tiny holes, then the young wasps have already left the nest.

One of the best ways to limit damage from gall wasps is just to cut back any affected branches to just behind the gall. Make sure you dispose of these in the bin.

While the gall wasp will not kill your tree, it can result in deformed branches that will not bear as many fruits.

Scale Insects

Scale are tiny brown or black insects with a hard coating. They look like small bumps on the leaves and stems.

Scale insect | Fruit & Vegetables

These are sap-sucking insects that can cause damage to your tree if left unchecked.

If you have a scale problem, you might also notice a proliferation of ants crawling on your lemon tree.

This is because the scale insects produce a sticky substance referred to as honeydew. The ants feed on this substance and also protect the scale insects from predators.

The best way to get rid of scale is to spray them with an oil-based insecticide such as white oil.

Large Citrus Caterpillar

The citrus butterfly caterpillar is green in colour with brown and white markings.

Large Citrus Caterpillar | Fruit & Vegetables

It feeds on the leaves of lemon trees and can defoliate the tree rather quickly. It also produces a nasty odour when disturbed.

Although this caterpillar will eventually turn into a lovely butterfly, you don’t want it defoliating your tree.

Therefore, you can either remove it by hand (watch the smell) or you can spray it with a pyrethrum-based insecticide.

Common lemon tree diseases

Luckily, there are not too many diseases that can commonly affect lemon trees. 

Melanose

This is a fungal disease that will affect the fruit, branches and immature leaves.

It presents as small dark brown spots that will eventually join to form large patches. Fruit that is affected will become inedible.

To control, cut off any affected branches and throw them in the bin.

Also, remove any leaves or damaged fruit that has dropped to the ground.

Then, spray your tree all over with a copper-based fungicide.

FAQ

How do you rejuvenate a lemon tree?

To rejuvenate a lemon tree, give it a good prune and remove crossing branches. Then, add a layer of mulch around the base of the tree that includes some well-rotted horse or cow manure. You can also add some wood ash to this. Water well and watch your tree flourish.

When should you not water a lemon tree?

Mature lemon trees growing in the ground should only need watering during summer when you’re experiencing long periods of dry weather. Water deeply once a week.

Photo of author

Annette Hird

Annette Hird is a gardening expert with many years of experience in a range of gardening related positions. She has an Associate Diploma of Applied Science in Horticulture and has worked in a variety of production nurseries, primarily as a propagator. She has also been responsible for a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.

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