The question of what causes black spots on tomatoes is a vexing one for a lot of gardeners.
In fact, the fruit of a growing tomato plant can develop more than one kind of black spot, and there are several possible causes.
The most common cause of these black spots is blossom end rot (BER).
In this case, the black spot appears on the bottom of the tomato where the blossom once was.
The spot usually has a sunken appearance and steadily grows in size.
It results in soft tissue that is often infected with fungal spores, and generally causes the loss of the fruit on which it appears.
Blossom end rot can be attributed to a lack of calcium uptake by the plant.
As calcium is present in sufficient quantities in most soils, it is generally soil dryness that causes the problem because it prevents the roots of the plant from absorbing the calcium that is present.
Well-watered soil will usually prevent the development of blossom end rot.
In the case of soil that is in fact calcium-deficient, lime should be applied around the plant.
What causes black spots on tomatoes that look more like with lines with a zipper-like appearance on the side as well as on the bottom of the fruit? This is catfacing, a result of damage to the plant at the beginning of its development.
Cold, cloudy, or wet weather, or poor pollination at blooming time can lead to catfacing.
Erratic soil moisture and temperature, too much nitrogen, and excessive pruning are other possible causes.
Any fruit that shows signs of catfacing should be removed from the plant.
Now, let's look at what causes black spots on tomatoes at the stem end.
If it looks like blossom end rot, but appears on the stem end, it is likely to be botrytis blight, also known as gray mold.
Once gray mold takes hold, it can spread quickly to all parts of the plant.
It cannot be cured once it has taken hold.
The best we can do is remove affected plants or parts of plants and then spray remaining healthy-looking plants with a fungicide (labelled for use on edible plants).
It is important then to rotate crops for the next season, as the gray mold fungus can survive the winter and remain in the soil.
In fact, the fruit of a growing tomato plant can develop more than one kind of black spot, and there are several possible causes.
The most common cause of these black spots is blossom end rot (BER).
In this case, the black spot appears on the bottom of the tomato where the blossom once was.
The spot usually has a sunken appearance and steadily grows in size.
It results in soft tissue that is often infected with fungal spores, and generally causes the loss of the fruit on which it appears.
Blossom end rot can be attributed to a lack of calcium uptake by the plant.
As calcium is present in sufficient quantities in most soils, it is generally soil dryness that causes the problem because it prevents the roots of the plant from absorbing the calcium that is present.
Well-watered soil will usually prevent the development of blossom end rot.
In the case of soil that is in fact calcium-deficient, lime should be applied around the plant.
What causes black spots on tomatoes that look more like with lines with a zipper-like appearance on the side as well as on the bottom of the fruit? This is catfacing, a result of damage to the plant at the beginning of its development.
Cold, cloudy, or wet weather, or poor pollination at blooming time can lead to catfacing.
Erratic soil moisture and temperature, too much nitrogen, and excessive pruning are other possible causes.
Any fruit that shows signs of catfacing should be removed from the plant.
Now, let's look at what causes black spots on tomatoes at the stem end.
If it looks like blossom end rot, but appears on the stem end, it is likely to be botrytis blight, also known as gray mold.
Once gray mold takes hold, it can spread quickly to all parts of the plant.
It cannot be cured once it has taken hold.
The best we can do is remove affected plants or parts of plants and then spray remaining healthy-looking plants with a fungicide (labelled for use on edible plants).
It is important then to rotate crops for the next season, as the gray mold fungus can survive the winter and remain in the soil.