Black spots on lemon tree leaves can signify several diseases, all quite dangerous. It’s essential to quickly identify the ailment attacking your garden and take emergency measures.
Unfortunately, there’s so much work in the garden and vegetable plot during the summer that few gardeners regularly inspect their lemon trees.
They are alive, bloom, and produce foliage – and that’s great. This is why the first signs of disease often go unnoticed.
To detect problems in time, it’s necessary to walk through your garden at least once every two weeks, inspecting not only the trunk and main branches but also the leaves, flowers, and fruits.
Black Spots on Lemon Tree Leaves
While black spots on the bark are clear-cut, the leaves of lemon trees can be affected by many more diseases.
In addition to black canker, such effects are typically caused by several fungal or bacterial diseases.
However, the buds and flowers of lemon trees turn black only in case of severe spring frost.
All pests that eat buds leave brown or reddish traces. You must protect the garden from recurrent frosts to avoid frost damage to flowers.
Recognizing scabs is quite easy, as virtually every gardener has seen fruits or leaves affected by this disease at least once.
Besides, lemon, apple, and pear trees are most often affected by scabs, and there are cases where a seedling was infected while still in the nursery.
So, you can identify scabs by the dark, brownish, gradually blackening spots that cover the leaves as early as spring and multiply with each passing week.
The fruits of an infected lemon tree stop developing, darken and become unfit for consumption or composting.
Treat lemon trees with Bordeaux mixture immediately after detecting the first brown spots. The first treatment is done with a 3% solution at the beginning of the bud break.
Immediately after flowering, spray trees with a 1% solution, and 2-3 weeks after lemon trees have bloomed, you should spray with a copper fungicide (Amazon link)following the instructions for use.
Bacterial Blight (Bacterial Canker)
It’s pretty easy to spot powdery mildew, as practically every gardener has seen fruits or leaves affected by this disease at least once.
Besides, lemon, apple, and pear trees are the most common victims of powdery mildew, and cases where a seedling was infected while still in the nursery are pretty widespread.
So, you can tell a lemon tree has powdery mildew by the dark, brownish-black spots that gradually darken and cover the leaves in spring and only worsen with each passing week.
The fruits of an infected lemon tree stop growing, turn dark, and become useless for eating or composting.
To treat your lemon trees for powdery mildew, apply the Bordeaux mixture when you spot the first brown spots. Use a 3% solution of the preparation at the beginning of the bud break.
Once the lemon trees start flowering, spray them with a 1% solution, and 2-3 weeks after trees bloom, treat them with Copper-containing products at 3-week intervals between April and July for lemon canker management. Still, there is no cure for the disease.
Bacterial Leaf Scorch (Bacteriosis)
When a bacteriosis affects the lemon tree, the entire plant looks scorched – leaves, branches, trunk, and fruits.
First, the whole lemon tree is covered in black spots, then the leaves curl up and fall off. The fruits darken, stop developing, and spoil.
If the lemon tree is affected entirely, it’s best to uproot and burn it immediately.
However, if the disease has only begun to spread, there’s still hope to fight it. Start by cutting off the affected parts of the lemon tree.
Treat the cut area with a 1% solution of copper sulfate, then apply a 5% solution of AzoFos twice a month to the lemon tree.
If you notice a black sticky coating covering all the leaves and fruits of your tree, that’s a sign that aphids have taken over and brought spores of the ring spot fungus.
This disease most often affects seedlings, young trees, or weakened specimens.
But don’t despair because you can treat this disease quickly. According to the instructions, apply Fertilome Broad Spectrum Fungicide (Amazon Link) twice to the lemon tree.
Remember, acting quickly to prevent the disease from spreading and causing further damage to your lemon trees is essential.
Black Spots on Lemon Fruits
In addition to the previously mentioned diseases that affect both leaves and fruits, one disease can only be detected on the fruits themselves – sooty mold.
Of course, it has nothing to do with flies; it’s a typical fungus named for its resemblance to insect excrement. However, no matter how hard you try, you won’t be able to wipe it off the affected lemons.
Clusters of black spots appear on fruits growing in old, over-watered, shaded, poorly-ventilated gardens. Heavy dew or prolonged rain can also trigger the infection.
This disease is not dangerous to humans; the affected fruits do not lose their taste or shelf life; only their appearance worsens.
To protect the garden, timely sanitary pruning is usually enough. However, if the infection is extensive, you must treat the lemon trees with strobilurins according to the instructions.
A 1% Bordeaux mixture and colloidal sulfur are slightly less effective, but you can apply them if necessary.
Black Spots on Lemon Tree Bark
The saddest thing that can happen to fruit trees in a garden is the appearance of black spots on the trunk or main branches.
At first, they’re small (up to 0.4 inches in diameter), slightly concave, and have a purple hue. Over time, they gradually expand, affecting a larger area. This symptom indicates a disease called black canker.
At the site of the infection, the bark first turns black, and then the disease penetrates deeper layers. The bark starts to crack and peel away in shreds.
The branches or trunk die off, leaving wounds on the lemon tree. At this stage, the leaves and fruits also turn black if present.
Although black canker is believed to be a disease of weakened lemon trees, the fungus can infect any plant in the garden.
Sometimes, a lemon tree has healed itself from canker wounds, but they are scarce, so relying on a miracle is not wise.
You should immediately start treatment at the first signs of black canker on a lemon tree.
Scrape the affected areas with a knife down to the healthy wood. Disinfect the wound with a 5% solution of iron sulfate.
Do not seal the lemon tree wound with anything because it will do more harm than good.
The lemon tree will naturally produce callus to heal itself. With a one-month interval, treat the lemon tree twice with a 1% Bordeaux mixture.
Remember, whatever the cause of black spots on the lemon tree in your garden, it won’t “disappear” on its own. By delaying, you are only putting all your plants at risk.
Encountering yellow spots on your lemon tree leaves? Explore solutions in our article: Fixing Yellow Spots on Lemon Tree Leaves