Identifying And Treating Greasy Spot Fungus

Image by Pat Barkley

By Kathleen Mierzejewski

Citrus tree diseases are quite common among orange, lime and lemon trees. These trees are hardy enough, but they end up with citrus fungus diseases easily if the right conditions allow for it. The reasons you want to prevent fungus from forming on your citrus tree are because they can cause severe leaf drop and eventually kill your tree. The most common form of citrus tree fungus is greasy spot fungus.

Greasy Spot Fungus

The fungus caused by greasy spot is caused by the fungus Mycosphaerella citri. Whether you grow citrus trees for a fresh fruit market or processing plant or just for your own use, you need to be able to control greasy spot fungus. If you allow the fungus to simply live, you will end up with a ruined fruit crop.


Grapefruits, pineapples and tangelos are most susceptible to greasy spot than other varieties of citrus fruit plants. However, just because you grow lemons and limes doesn’t mean your plants are safe. Citrus tree fungus can run rampant among all your citrus trees.

What happens is greasy spot causes airborne ascospores to be produced in decomposing leaves. These leaves will be on the grove floor or the ground below your tree. They are a primary source for greasy spot to inoculate your trees. The warm dampness on a humid summer night is the perfect atmosphere for these spores to grow.

The spores will germinate under the leaves on the ground. This particular citrus tree fungus will grow on the surface of the ground leaves for a while before they decide to penetrate through the openings on the lower leaf surface. At this point, greasy spot can become a devastating citrus fungus disease.

Symptoms won’t appear for many months, but once it does, black spots will be seen on the leaves of your trees. If it is allowed to fester, you will start noticing the leaves falling off your trees. This is no good for the tree.

Citrus Fungus Treatment

Treatment for greasy spot fungus is easy enough. The best treatment around is to use one of the copper fungicides out there and spray the tree with it. Use the copper fungicide according to directions in order to kill the citrus tree fungus. This treatment does not harm the tree, and other than a little leaf drop, you should clear up the greasy spot disease in no time.

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