brown/tan spots on tomato bottoms

Asked August 1, 2018, 11:25 PM EDT

I have just harvested my first few tomatoes and on one tree the tomatoes are brown or tan on the bottom. Someone once told me that this could be due to too much water. I don't believe I have over-watered and the trees adjacent to this one do not show signs of this. Any information or recommendation would be greatly appreciated.

Lane County Oregon

1 Response

This is blossom end rot, a physiological disorder related to calcium. Some varieties, especially large tomatoes, are more prone to it. It occurs with erratic watering (dry then too wet, then too dry, with sudden temperature swings like the very hot weather we just had. In that case, the plant withdraws water from the developing fruit for its leaves and transpiration. This causes the death of the cells at the blossom end of the tomato. If the tomatoes are almost ripe, pick, trim off the bad and eat. If they are still quite green, you can salvage the good part for fried green tomato, salsa etc.We tend to grow cold-tolerant tomatoes here so that acerbates the situation. There is a calcium foliar spray which can be applied to unaffected tomato plants which may help.

The following is from OSU.

A localized calcium deficiency due to any soil or growing condition that affects calcium uptake. This physiological problem is common, especially in home gardens. Blossom-end rot often occurs when soil moisture fluctuates. If too little calcium is in the soil or if the soil is high in salts, calcium uptake will be impeded, especially under periods of sudden drought stress. Excessive nitrogen applications, especially in the ammonium form, can increase a plant's demand for calcium. Once calcium is used in the plant, it becomes immobilized and cannot be translocated from older tissues to younger, growing tissues, which need calcium.

Symptoms A water-soaked, light tan spot at the blossom end or side of a fruit. The spot enlarges, becoming dark brown or black and leathery. Normally, spots are dry but may become soft if secondary bacteria and fungi invade the fruit. Affected fruit ripen faster than normal.