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Having grown a bay tree in a pot for over 5 years, with relative success, I noticed in early spring 2023 that black spots had started to appear on some of the leaves. So, I started looking into the the possible causes and remedies for this. I wanted to restore my bay tree back to full health as quickly as possible!
Black spots on bay tree leaves can be caused by several different conditions such as sooty mould, shot hole disease and leaf spot disease.
This is What the Black Spots on my Bay Tree Leaves Looked Like
The severity of the black spots on my bay tree varied from leaf to leaf. I had leaves that were unaffected, leaves with smaller spots and leaves with a larger spots, (or blotches). The spots were on both sides of the affected leaves. There were no holes in the leaves and they didn’t seem to be curled over at the edges. See the pictures below!
Top 3 Causes of Black Spots on Bay Tree Leaves
I identified the top three possible causes of the black spots on my bay tree leaves, which are sooty mould, shot hole disease and leaf spot disease. The earlier you identify these diseases, the easier they will be to treat. Let’s look at them one by one…
1. Sooty Mould
– Identification
As the name suggests, sooty mould manifests itself as a layer of sticky, black, soot-like mould on bay tree leaves. This sooty layer can be wiped away from the leaf using water or a weak soapy liquid.
Looking at my tree, I ruled this out as a possible cause straight away. There is no coating or sooty layer on the leaves, and if I wipe the leaves, the black spots remain and will not come off.
– Root Cause
Sooty mould is most prevalent in the summer and the root cause will be bugs, insects or aphids living on the leaves of the tree. If present on your bay tree, they can usually be found on the underside of the leaves. They excrete a sticky honeydew over the leaf surface which attracts airborne fungus spores. The fungus then feeds on the honeydew resulting in the growth of soot-like mould.
I have checked all of the leaves on my bay tree and there is no evidence of insects, bugs or aphids.
– Prognosis
Sooty mould on bay tree leaves is more of a cosmetic condition. While the mould itself can affect photosynthesis by blocking light from the leaves, as long as it is not left untreated for a prolonged period, it shouldn’t cause significant long term damage.
– Solution
If you have identified a sooty mould problem on your bay tree, just wiping away the mould will not fully eradicate the problem: only dealing with the bug / insect / aphid infestation and stopping the excretion of sticky honeydew will keep sooty mould away.
You may find that wiping down the affected leaves is enough to remove any bugs / insects / aphids. If they persist you can try applying neem oil, which is a natural and environmentally friendly insecticide, to remove them. Neem oil can be used on edible plants, as long as the usage and application instructions are followed exactly!
Shop for neem oil on Amazon below:
2. Shot Hole Disease (aka Coryneum Blight)
– Identification
Shot hole disease can affect the branches, stems, buds and leaves of bay trees. You are most likely to notice the first signs of it on the leaves. It causes purplish leaf spots to appear across the leaf which then grow and develop, eventually dropping from the leaves entirely to leave small round holes (hence the name “shot hole”). You will see multiple small holes randomly scattered over the affected leaves.
I discounted shot hole disease as the cause of my leaf spots as there were no actual holes present on the affected leaves.
– Root Cause
Like sooty mould, shot hole is a fungal disease. However, there are no insects or aphids involved in causing the damage in cases of shot hole disease. In shot hole disease, airborne spores attach themselves to leaves and rain and wind then enable their spread to branches, stems and buds. Once fungus develops from these spores it will take hold. It will thrive when conditions are wet, and symptoms are most often first seen in the springtime.
– Prognosis
Unfortunately leaves affected by shot hole disease will not recover. As the fungus continues to take hold it will eventually damage leaves to such an extent that it will cause them to die and fall from the tree. Shot hole disease will affect photosynthesis and will severely restrict the growth pattern of the tree, getting progressively worse unless action is taken to combat it.
– Solution
If you identify shot hole disease on your bay tree the best natural treatment approach is to remove any affected leaves, stems and buds (affected buds will be darker in colour than healthy buds). These should all be disposed of away from the tree to prevent any further contamination through spores re attaching themselves to healthy parts of the tree. Any debris around the base of the tree should also be removed and treated in the same way.
The presence of excess moisture will facilitate the spread of shot hole disease:
– In periods of prolonged wet weather it is worth regularly checking the condition of the leaves.
– Be sure not to overwater, and when you do water try watering at the base of the tree so as not to get unnecessary moisture on the leaves.
– Also, ensure that pots are freely draining: pot bound trees or blocked drainage holes can cause water to gather, potentially rotting the roots and providing ideal conditions for fungal disease to spread.
3. Leaf Spot Disease
– Identification
Leaf spot disease causes small black spots to develop on bay tree leaves. As the disease progresses the spots will get larger until they start to join up and resemble blotches. Leaves will remain intact overall without the presence of holes in their surface.
Looking at the condition of my leaves, I think that I have a case of leaf spot disease affecting my tree:
– Root Cause
Leaf spot disease is fungal. Airborne spores become attached to bay tree leaves, and when conditions are wet and air circulation low, fungus will take hold. Bay trees in pots with poor drainage are especially susceptible as waterlogged growing conditions will help enable the establishment and spread of leaf spot disease.
The fungus can produce it’s own spores when mature which can in turn spread to new, uninfected, leaves via either wind or rain.
– Prognosis
Affected leaves will not recover and should be removed. Leaf spot disease will rarely affect a 100% of leaves, but will restrict the growth pattern of the tree.
– Solution
As with shot hole disease, the best natural approach to treating leaf spot disease is to remove affected leaves from the tree. As the disease is fungal in nature the leaves should be disposed of away from the tree to prevent any cross contamination through spores re attaching themselves to healthy leaves. Any leaf debris around the base of the plant should be treated in the same way.
The presence of excess moisture will facilitate the spread of leaf spot disease:
– In periods of prolonged wet weather it is worth regularly checking the condition of the leaves.
– Be sure not to overwater, and when you do water try watering at the base of the tree so as not to get unnecessary moisture on the leaves.
– Also, ensure that pots are freely draining: pot bound trees or blocked drainage holes can cause water to gather, potentially rotting the roots and providing ideal conditions for fungal disease to spread.
This is What I Did to My Bay Tree After Identifying Leaf Spot Disease
My bay tree had already recently been repotted so I knew that the roots were not pot bound and the drainage holes inside the pot were not restricted. For more information on repotting bay trees, follow this link to our article: how to repot a bay tree.
After identifying leaf spot disease, the first thing I did was to start removing the affected leaves, making sure that I safely disposed of them away from the tree.
Unfortunately there were quite a lot of damaged leaves so, once they were removed, I decided to further prune and shape the tree. My tree had become somewhat overgrown and I wanted to achieve a “lollipop” shape instead of allowing it to develop into a bushy shrub.
The best way to prune a bay tree is to cut leaves back to a new bud. Pruning can be carried out at any time during the growing season (early spring to mid summer). The direction of the bud that you cut back to will determine the direction of the new growth post pruning.
As well as improving the shape of the tree, pruning will have the additional benefit of improving air flow and minimising moisture levels on the leaves and branches.
This is what my bay tree looked like when I had finished pruning:
To help ensure good drainage, I raised the pot slightly off the ground using pot feet. Pot feet allow you to easily and evenly raise the pot and the feet that I used are not really noticeable when in place. The gap that they create is a great help when it comes to preventing the drainage holes at the bottom of the pot becoming blocked – helping to prevent waterlogging:
The pot feet that I used are available on Amazon below. I used 6 pot feet in total (3 blocks of 2). You can vary the height of the pot by using more or less pot feet, depending on your requirements.
In Conclusion
So now, after discovering black spots on some of my bay tree leaves, I have taken steps to try and provide it with the best chance of recovery. I opted to use natural, non – chemical, options to bring the leaf spot disease under control as the bay tree is classed as an edible crop and I will hopefully be using future (healthy) leaves in cooking.
It is worth remembering that although the steps I have taken will have significantly reduced the impact of leaf spot disease on the tree, it may not be completely eradicated. I will continue to monitor the leaves, especially during wet weather, and remove any further leaves that may become affected. And I will continue to look after the general health of the tree ensuring it has the correct water levels and nutrients that it needs to thrive.
It will then just a waiting game to see how it does over the coming year!
More Articles And Information On Bay Trees
Links to our other bay tree related articles are below – why not check them out?
Why Have my Bay Tree Leaves Turned Brown?
And Finally….
If you are looking to add more bay trees to your garden space, take a look at bay trees in pots available on Amazon here!
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