The horticulturists are available through the ISU Hortline to answer additional questions. Contact them at hortline iastate. Blossom end rot is probably responsible for the blackish spots on the tomato fruit.
If you have tomatoes turning brown on the bottom then you are not alone. This time of year we have many calls about brown spots on tomatoes, squash, peppers, watermelons, etc. This is called blossom-end rot BERwhich is a nonparasitic disease of tomatoes and other fruiting vegetables.
Many a tomato gardener has been taken aback by the appearance of blossom-end rot. This condition, characterized by a large, brown lesion at the blossom end of the tomato -- opposite the stem -- disfigures the fruit and makes it unpalatable. Though it looks like a fungal disease, blossom-end rot is actually an indication that calcium is in short supply.
A water soaked spot at the blossom end of tomato fruits is the classic symptom of blossom end rot. This relatively common garden problem is not a disease, but rather a physiological disorder caused by a calcium imbalance within the plant. My heirloom tomatoes are starting to ripen but they have ugly black spots on the bottom.
Why are your tomatoes rotting on the bottom? Unfortunately, they probably have blossom-end rot. Calcium is needed for normal cell growth.
Who put this disgusting black scab on the bottom of my beautiful tomato? Blossom end rot is caused by two things: a lack of calcium and inconsistent watering. However, you can still save the plant and any remaining tomatoes it produces.
The affected tissue breaks down rapidly and the area becomes sunken, dark brown or black, and leathery. This can happen at any time as the tomatoes mature, and most often on the first tomatoes of the season. Blossom-end rot is caused by insufficient calcium in the tissue of the tomato.
While annoying, blossom end rot BER is treatable and preventable. Caught early, your odds of a successful tomato crop are still good. Your black bottomed tomato has blossom end rot. Blossom end rot is caused by the tomato plant not being able to get enough calcium to the developing fruit.
Biting into slices of freshly picked, ripe, juicy tomatoes from the garden is one of the great pleasures of life. You cannot help feel depressed and disappointed if your tomato plants wilt and the fruits rot on the vine. Common fungal diseases, such as early blight, late blight and fusarium wilt, cause wilting and rotting of tomatoes.