Lemon tree diseases and pests

Last updated on March 29th, 2022

If you are growing a lemon tree no doubt you have a great appreciation for the fragrant blooms and the delightful fruit it has to offer. Unfortunately, there are many pests that are just as excited to have a lemon tree nearby.

Some of the biggest pests are relatively harmless (like aphids) but there are some more serious like the citrus rust mite that will affect the fruits rather than the foliage. Knowing what pests and diseases pose a potential threat to your plants will help you to utilise the most effective preventative measures and subsequent treatments if an outbreak is discovered. 

Pests

Aphids

Aphids are one example of a lemon tree pest. You will see large clusters of these incredibly small insects living on new foliage at the beginning of spring. If they aren’t controlled by natural predators or fruit safe pesticides they can damage younger trees.

Thankfully, you can release ladybirds to control the aphids as an organic treatment option or use a fruit safe pesticide designed to kill aphids such as greenflies and whiteflies. The problem with aphids is that it also leads to the sooty mound if left uncontrolled. Leaves that are badly affected (like the ones pictured above) are best removed.

Citrus leafminer

If you notice that the leaves on your lemon tree have started to curl (like the picture above) and there are tiny passageways carved into the foliage it’s indicative of the citrus leafminer.

As the name suggests, these pests literally mine their way through the leaves and in doing so carve through the outer layers and eat the soft tissue underneath. They won’t harm a mature, established tree as much as a younger tree. If you have a new tree, be on the lookout for them because they can severely weaken your tree and eventually kill it.

Again, natural predators go a long way toward ridding your lemon trees of any insect problems. With the citrus leafminer, you can introduce a parasitoid wasp.

Other methods of treatment include spraying your tree with an oil spray. There are certain natural oils you can mix with water or combinations of washing up liquid and water for outbreaks of aphids. Horticultural sprays are another option equally effective at treating pests like the citrus leafminer. 

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Diseases

Aside from pests you also have to worry about different diseases. The bad news is there are a plethora of diseases that affect lemon trees, ranging from things like nutritional deficiencies to fungal infections. Knowing how to identify the symptoms of different diseases and what treatments are most effective will go a long way toward helping you mitigate any potential side effects they might have. 

Citrus Canker

Citrus Canker is very contagious. It will manifest in the form of yellow lesions in the shape of halos on almost all parts of the tree. If you don’t rectify it quickly the tree will die back, lose its leaves, and drop all of its fruit. The problem with this disease is that it spreads through the air. When the wind blows, a bird or an insect touches the plant, or you run your hand over it, it gets moved and transferred from one place to another. You can prevent this by spraying liquid copper fungicide. If your tree already has the infection, unfortunately, there is no treatment and you will have to destroy it.

Greasy spot fungus

Greasy spot fungus is a fungal disease that manifests with yellow-brown blisters on the under part of the leaves. As it progresses the blistering starts to take on an oily appearance, hence the name. Liquid copper fungicide is the best way to treat this. You should spray it in June or July and then again in August or September, even if your plant doesn’t show any symptoms. Remember that preventative measures are most effective where these diseases are concerned.

Sooty mould fungus

Sooty mould fungus is a fungal infection that turns the leaves black. This is the result of aphids or mealybugs. To eradicate it you need to start by controlling the infestation of insects, after which you can spray your tree with neem oil insecticide all over, including the underside of the leaves. Repeat the process every 10 days contingent upon the extent of your infestation. Once the insects have been eradicated you can follow up by treating the citrus with a liquid copper fungicide.

Phytophthora fungus

Phytophthora fungus is a form of root rot that’s caused by a fungal infection. You will notice dark brown patches that are very hard to touch on the trunk of your tree. Eventually, these patches start to ooze. As the disease continues to progress these patches will crack and die resulting in sunken areas on your tree.

The fruit might also start to decay. This fungus lives in the soil so if you have particularly wet soil that gets splashed up onto the tree, it starts to form dark patches. In order to treat this, you need to remove any infected leaves and fruit, prune the lower branches that are more than ¾ metre from the ground. Spray the entire plant with a fungicide. 

Botrytis fungus

Botrytis fungus is something you might notice after a heavy downpour, and it starts to affect developing blooms in the spring. For this, you want to spray with a fungicide as well.

Anthracnose

Anthracnose is a fungal infection that manifests in Leaf Drop, stained fruit and stems dying back. It usually happens after an extended rainy period that can be treated with a fungicide.

With almost all of these, preventative measures will prove most effective and the application of liquid copper fungicide is one of the most recommended methods to try. Remember to remain consistent with feeding schedules and irrigation, monitor your tree for any pests and treat at the very first signs of an infestation. Always remove the debris from around the tree and get rid of any weeds nearby where a fungal disease might live. The small efforts throughout the year will go a long way toward preventing significant and perhaps irreparable damage to your citrus tree.

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Other citrus tree problems

Citrus trees can also suffer from more environmental problems caused by the weather, incorrect watering and feeding.

Learn about citrus tree problems in this guide.

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