Learn what causes black spots on mangoes and leaves, their symptoms, prevention and treatment. My mango tree in Sydney, Australia gets these black spots. Can you eat mangoes with black spots? Know whether they are harmful or safe to eat. The black spots on mango tree are usually due to a fungal infection or a bacterial infection.
Once the tree is infected, then it becomes difficult to get rid of it completely in a short time, even with proper care (mango tree care).Causes of Black Spots On Mangoes
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| Black Spots on Mangoes |
The fungal infection is caused by the fungus Colletotrichum gloeosporioide, called as anthracnose which can infect not only mango fruits, but also roots, leaves, stems and twigs [1].
High humidity, high moisture levels in the garden and poor hygiene practices can cause black spots on mango trees.
The anthracnose cause black spots not only on mangoes but on many tropical fruits including avocado, banana, coffee, papaya, passion fruit, etc. This fungus may help protect the tree from other diseases and pests.
Other Causes of Black Spots on Mango
Many times the black spots on the fruits may be a result of sunburn, which begins as a red blush on the skin and then end up as a large black spot.
Rain and wind can also cause skin deep tiny marks on the fruit.
Symptoms of Anthracnose
The black spots due to anthracnose fungus are circular and uniform, whereas irregular spots accompanied by a foul odor are due to bacterial infection.
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| Mango Anthracnose vs. Bacterial Black Spots |
The signs or symptoms of anthracnose appear as small dark, sunken spots or lesions on leaves and fruit which become larger over time. The fungus can enter the fruit through wounds or stem scar.
Small, immature fruit do not show spots until fruit ripens. Fruits showing up black spots after harvest is the result of infection of fruit on trees before harvest.
Prevention of Black Spots
The presence of anthracnose disease on the tree will drop flowers and fruits prematurely from the tree. To prevent black spots on mangoes and leaves, note the following:
- Anthracnose thrives in cool, moist climates.
- Overwatering and watering over the foliage invite bacteria and fungus.
- Poor air circulation can cause anthracnose.
- Ensure good air circulation and proper watering to prevent anthracnose.
- Prune out dead wood before flowering. Prune to keep the canopy open helps to reduce the severity of infection (how to prune mango tree).
- Prune all the infected leaves and branches and destroy them. Do not put them in your compost bin. Disinfect the cutter after pruning to prevent spreading of the disease to other plants.
- Touching infected leaves and then handling healthy plants will infect those plants, so always wash your hands thoroughly after you touch infected mango tree.
- Remove the infected fallen leaves, flowers and twigs under the tree and destroy them to avoid the risk of spreading the disease to other plants in the garden.
- A healthy and thriving mango tree will be able fight the disease, so fertilize it correctly (how to fertilize mango tree).
How to Treat Anthracnose
Anthracnose is one of the most common diseases in a garden. It requires to control anthracnose, both pre- and post-harvesting. The question is how to treat black spots on mango tree.
The anthracnose disease spreads during wet spring or if the foliage remains wet. During dry weather, the anthracnose disease goes away or slows down or even may disappear. But the anthracnose will return again if the humidity becomes high it rains.
Fungicide Sprays that Kills Anthracnose
There are some fungicides that can treat anthracnose. The most effective and best fungicides for control of black spots are copper based fungicide, prochloraz fungicide and mancozeb fungicide.
Spray the fungicide on the tree right from the panicle emergence to 2 weeks before the harvest every 2 weeks.
Mancozeb is recommended on a weekly basis in Australia to treat anthracnose. [1]
Neem Oil is also an effective fungicide for the prevention and control of anthracnose besides control of black spot on roses, powdery mildew, rust, needle rust, scab, etc.
I spray a mixture of copper fungicide and neem oil on my mango tree every 3 weeks.
You can also try a baking soda spray.
Homemade Copper Fungicide Sprays
Bordeaux mixture, Copper Fungicide
This homemade fungicide is called the Bordeaux mixture which can be used to control fungal diseases such as black spots, powdery mildew, and rust on vegetables, fruits, indoor plants and all other plants.
It is a safe and effective way to treat diseases such as black spots, powdery mildew, and rust.
The Bordeaux mixture is prepared by mixing 100 gram of copper sulfate and 100 gram of lime in 1 liter of water.
Post Harvest Treatment of Black Spots
The black spot disease on mango continues even after you harvest the fruit. The spots may not be seen on mangoes when you harvest them, but they show up as the fruit ripens. Fruits showing up black spots after harvest is have been because they infected on the tree before harvest. Prochloraz is used as a cold non recirculating spray. To prevent and control this you can do the following:
Post Harvest Hot Water Treatment
The harvested fruit may be treated with vapor heat, forced-air dry heat and hot water dips. In the hot water treatment for disease control, the fruit are dipped in hot water at 49 to 55°C (120-131°F) for 5 to 15 minutes depending on mango cultivar [2, 3, 4].
Hot benomyl dips can control anthracnose and stem end rots.
Post harvest treatment by Essential Oils
Treating the harvested mangoes with certain essential oils like ginger oil, lemongrass oil, savory oil, thyme oil could cure the disease [5].
3. Baking Soda Spray
I have tried spray of baking soda on my harvested mangoes with some success.
Are Mangoes with Black Spots Safe to Eat?
No body prefers to buy mangoes or for that matter any fruit with dark spots on them from grocery store. They do not look good and are not appealing. Some people may consider mangoes with black spots as unhealthy and prefer not to risk consuming them.
Is Anthracnose Harmful?
Anthracnose is harmful to plants but poses no harm has been reported to people. Anthracnose is one of the main reasons of flowers not getting pollinated, falling of flowers and premature fruit drop (causes of mango fruit drop), resulting is reduced crop and fruit with spots.
My mango tree, because of frequent rain in Sydney, produced black spots on the leaves, flowers and fruit. The fruits were perfectly alright with no spots until they became fully ripe. They started to develop black spots as they began to ripen on tree and these spots continue to grow in size even after picking them from the tree.
Mangoes with Black Spots Safety
So I experimented on such dark spotted mangoes to see if they are suitable for consumption. I observed the following, which may be important for safeguarding one’s health:
The mangoes with black spots are usually totally safe to consume if the spots are not too severe and deep. The fungus that causes these black spots remain generally on the surface of the skin of the fruit. I eat mangoes having dark spots, they look and taste as good as the ones without spots. I and my family eat them without hesitation.
Before consuming mangoes with black spots, you may consider the following points:
Look at the severity of spots: First assess the severity of black spots, are they small or large, localized or on whole fruit, on the surface or deep inside?
If the black spots are confined to a small portion on the surface of the mango, it may be safe to eat.
If the spots are on a large portion of the mango, even then it may be safe to eat provided the spots are only on the surface of the fruit and have not penetrated into the fruit.
If the mango is ripe and firm, and the portion of mango with spots is also firm and not soggy, it may be good to eat. You may cut away the affected area before eating.
Large, deep and wet spots on a mango indicate spoilage, it is best not to eat such mango, destroy it.
If the fungus penetrates through the fruit, then they become unsuitable for eating.
After peeling the mango, if you notice any dark portion inside the fruit, that means the fruits has started to rot. Don't eat this mango, discard it in trash.
If you see, black veins (strings) in mango flesh, don't worry, these are vascular canal discoloration [6]. Such mangoes are safe to eat.
How to Eat Mangoes with Black Spots
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| Mango with black spots, good from inside. It tastes good. |
Peel the skin of the mango, then cut it in smaller pieces and consume. Don't forget to destroy the skin; do not put in compost bin.
Risks
Eating mangoes with black spots can pose some risks depending on the cause and severity of the spots. Following are the main risks for your health:
1. Eating the infected mango with black spots can cause symptoms such as abdominal pain, diarrhea and vomiting. However, we never had such symptoms after consuming such mangoes, because we always took care of the above points before eating them.
2. You may have allergic reactions such as itching, hives, and swelling if you are allergic to the fungus that causes black spots.
It is therefore important to exercise caution if you consume mangoes with black spots. It is always best to discard any affected areas before consuming the rest of the fruit.
Conclusion
Mangoes with black spots can be enjoyed, provided you take proper precautions before consuming them. You should carefully look for signs of fungus growth and its severity.
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References
1. D.M. Persley, K.G. Pegg, and J.R Syme, Fruit and Nut Crops, A Disease Management Guide. Queensland Dept. Primary Information Series QI88018. 68 pp, 1989.
2. Rappel, L.M., Cooke, A.W., Jacobi, K.K. and Wells, I.A. (1991). HEAT TREATMENTS FOR POST HARVEST DISEASE CONTROL IN MANGOES. Acta Hortic. 291, 362-371. DOI:10.17660/ActaHortic.1991.291.41
3. Wayne Nishijima, Mango Diseases and Their Control
4. Pennock, W. and G. Maldonaldo. 1962, Hot water treatment of mango fruits to anthracnose decay. J. Agriculture Univ. Puerto Rico 46:272-283.
5. Alice Ciofini, Francesca Negrini, Riccardo Baroncelli, and Elena Baraldi, Management of Post-Harvest Anthracnose: Current Approaches and Future Perspectives, Plants (Basel). 2022 Jul; 11(14): 1856.
6. Macnish, A.J., McConchie, C.A., Hofman, P.J. and Joyce, D.C.. Potential factors that contribute to resin canal discoloration in mango fruit. Acta Hortic. 1183, 311-318 (2017). DOI: 10.17660/ActaHortic.2017.1183.45