First there was torrential rain that ruined quite a few tomatoes but now the problems continues. It doesn’t seem the same thing as blossom end rot as it is found all over the fruit. What causes it?
Thank you for sharing your photo and I’m sorry to hear you are struggling to get good tomato fruits this summer.
This Might Be Blossom End Rot
It’s possible this is still blossom end rot (BER) – your photo looks a lot to me like the characteristic lesions of BER. BER lesions sometimes occur on the side or interior of fruits. I’ll share a summary of what blossom end rot is and then address what else it might be below that. Blossom end rot is due to adverse growing conditions and often occurs when fruit develops rapidly in periods of inconsistent watering. Though we have had significant rain this summer, we’ve also had periods of no rain. Here’s more from a past Toronto Master Gardeners post on blossom end rot:
“The ultimate cause is calcium deficiency, which – in the fruit itself – disrupts the permeability of the cell membrane, resulting in cell swelling, leakage and ultimately breakdown of membrane. As well, fewer new cells grow. This results in black, sunken areas of the fruit, which is vulnerable to attack by bacteria, fungi and pests.
Even if calcium is present in the soil , the plant cannot take up the nutrient if the soil is too dry, so fluctuations in watering are usually the preventable cause.
Since magnesium competes with calcium uptake, adding it is not only unnecessary but counterproductive.
Combatting blossom end rot is all about ensuring that the plant has a consistent source of water and good soil.
Good soil: If you are growing in pots, be aware there will always be a nutrient deficiency unless there is a fertilizer or compost added. Potting mix isn’t soil and has very few nutrients. Some people put the crushed shell of an egg in the hole at planting time and rotate the location of tomato plants each year.
Watering: Ensure the soil/potting mix is not allowed to dry out between watering (thus causing the plant’s roots to dry out inhibiting calcium uptake ). Conserve moisture around plant roots by mulching. Apply any fertilizer to moist soil – not to dry soil, as the concentrated nutrients can restrict the plant’s water uptake…and not too much fertilizer.
Finally, please remove the affected tomatoes immediately, to give other fruits the opportunity to develop normally.”
Other Causes?
It’s not uncommon for tomato plants affected by the stressors that lead to blossom end rot to be affected by other fungi or bacteria. Lesions on tomato fruit that resemble blossom end rot but are not located at the bottom could be caused by pathogens such as Colletotrichum fungi (anthracnose) or Phytophthora infestans (late blight).
It’s important to examine the overall health of your plants, including leaves, stems, and roots, to identify any other irregularities. Have you noticed any other symptoms on your tomato plants? Being able to see the condition of the other plant parts (and other fruits) could help identify the cause of this lesion. I’ll point you to a few solid scientific resources to help diagnose whether this is in fact something other than blossom end rot. If you determine that this is in fact another disease, be sure to do the following to prevent further spread or the repeat of this problem in your garden: 1) remove and destroy affected plants (in the garbage, not your compost or yard waste); 2) rotate where you plant your tomato crops in your garden or pots (do not reuse this same soil for tomato plants next year); and 3) plant disease-resistant varieties of tomatoes (the Cornell College of Agriculture and Life Sciences has a good list of examples).
Resources for Identifying Tomato Diseases
Tomato fruit rots, spots, and scabs (umn.edu)
Tomato Diseases45.pdf (missouribotanicalgarden.org)
Tomato Fruit Problems.pdf (missouribotanicalgarden.org)
Tomato Diseases & Disorders | Home & Garden Information Center (clemson.edu)