Why Do Mangoes Turn Black Outside (10 Reasons)

Mangoes develop dark spots due to damp conditions, bacterial infections, humidity, and several other factors.

However, lenticel darkening is the main reason why these spots appear, and some spotted mangoes are still edible.

So, keep reading to find out why your mangoes have dark spots, and how to know if your blackened mangoes are edible or not.

Why Do Mangoes Have Black Spots

Here are 10 reasons why mangoes have black spots.

Damp Conditions

Damp/wet conditions can cause mangoes to have dark spots. When the surrounding of the mango is wet, fungi like Anthracnose (Colletotrichum gloeosporioides) attack the mango, causing it to have dark lenticels on either or both of its inner and outer flesh.

Drought

When there’s a lack of sufficient soil water, mangoes may develop dark spots. 

The lack of water and increased temperature would prevent the mango from growing in size(ripening) which makes it decay on the tree. This decay is indicated by the growth of dark spots.

In some cases, this lack of water might also allow some pathogens to interact with the mango causing it to have dark lenticels.

Humidity

Mangoes, like other fruits, won’t grow under high humidity. When the amount of moist air is high, the mango’s growth may reduce temporarily. This temporary reduction in the expected growth time can make the cell walls of the fruit break, causing oxidation and the emergence of dark spots.

Strong Winds

Strong winds can make mangoes develop dark lenticels/spots in two ways:

  • Natural harvesting. When strong winds blow, ripe and unripe mangoes can be detached from their stem and drop to the ground. This drop makes bacteria and other pests interact with the mango. For ripe mangoes, the force at which it hits the ground can also cause dark spots.
  • Evaporation. High-velocity winds sometimes hasten the evaporation of water content from the soil, leading the mango tree to a state of temporary drought. This temporary drought can then lead to the emergence of some dark spots.

Chemical Burn

Mangoes develop dark spots when they come in contact with an acidic substance like their sap. The presence of sap on the skin makes the part affected develop weak skin which can cause dark spots.

Stem End Rots

Mangoes that were harvested from drier areas might develop stem end rots after their harvest. Stem end rots in mangoes are caused by fungi like Dothiorella dominicana, Phomopsis spp., Botryodiplodia theobromae, and Lasiodiplodia theobromae.

These fungi are natural habitants on the mango tree and grow their way into the stem of the fruit before it gets harvested. After harvest, they start attacking the mango, causing it to grow dark spots around its stem area.

Cuts/Puncture

Exposing any part of the mango due to a cut or puncture would cause dark spots. 

The opening caused by either of these two allows microbes to interact with the mango’s flesh, leading to discoloration. Alternatively, the presence of oxygen causes it to oxidize and start decaying. This can be noticed with the growth of dark spots.

Insect Sting

Insect stings from bees or fruit flies can make a mango grow dark spots. When these insects sting the mangoes, they leave a little opening which can make the fruit decay or oxidize leading to dark spots.

If the fruit gets a sting from an insect that carries a bacterium, it would also develop dark spots due to the presence of that bacterium in its flesh.

Bacterial Diseases

Bacterium infection on a mango can also cause dark spots. When the bacteria Xanthomonas axonopodis attacks a mango, the skin starts to grow black spots that have some amount of water in it.

Transport and Handling

If mangoes aren’t properly packed for transporting or properly handled, they develop black spots. These black spots can be caused by pressure placed on the mango, skin scratches, or rubs. When any of these happens, the polyphenol oxidase in the mango will combine with oxygen, resulting in black spots.

Can You Eat Mangoes with Black Spots?

Yes and No. 

In some cases, black spots on a mango indicate ripening which means you can eat it. On the other hand, these spots can be signs of rotting, indicating that you need to discard the mango. 

So, to be safe, cut into any mango with a dark spot before biting into it to avoid a horrid taste.

How Do You Keep Mangoes from Turning Black?

There are lots of ways to prevent a mango from having dark spots. Some of these preventive measures are:

  • Washing sap off the fruit and drying before storing.
  • Properly storing and avoiding excess pressure on the fruit during transport.
  • Spraying the surrounding with antifungal or antibacterial chemicals.
  • Removing infected trees before planting the next batch.
  • Preventive spraying of copper antibacterial products.

Don’t Toss Yet

Mangoes can still be savored even with the dark lenticels. In most cases, these dark spots usually affect the skin and leave the flesh as sweet and fresh as possible. 

So, don’t be quick to tag a mango as bad because it has a few dark spots. Rather, cut into it to verify its state and enjoy if it’s still edible.

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